Otherware

home *** CD-ROM | disk | FTP | other *** search

/ Otherware / Otherware_1_SB_Development.iso / amiga / info / trouble.txt / trouble

Wrap

Text File | 1992-11-11 | 60KB | 1,132 lines

Article 23236 of comp.sys.amiga.hardware: Path: access.usask.ca!kakwa.ucs.ualberta.ca!unixg.ubc.ca!ubc-cs!destroyer!sol.ctr.columbia.edu!spool.mu.edu!agate!stanford.edu!leland.Stanford.EDU!leland.Stanford.EDU!amigaman From: amigaman@leland.Stanford.EDU (Colin Gould) Newsgroups: comp.sys.amiga.hardware Subject: (VERY LONG!!! 60K) troubleshooting & DIY repair files Keywords: repair troubleshoot problems help Message-ID: <1992May27.074740.14720@leland.Stanford.EDU> Date: Wed, 27 May 92 01:47:40 GMT-0:04 Article-I.D.: leland.1992May27.074740.14720 Sender: news@leland.Stanford.EDU (Mr News) Organization: DSG, Stanford University, CA 94305, USA Lines: 1116 I replied a little while ago (re: Dead Amy! Help) regarding LED blinks, screen colors etc. on bootup, and included a bit of a do-it-yourself text file that listed a whole bunch of tips & tricks for amiga problems. I've gotten many requests for the files, so I decided to post them here. Note: they are VERY long! and a little old, but not too out of date. Hope I don't use too much bandwidth :-) but they should help a lot of people. I will include both files in this post. ----------------------------------------- Power-up operation summary (tests, LED blinks, screen colors) (Hans Hansen) Newsgroups: comp.sys.amiga Subject: Screen colors and other boot things Date: Wed, 15 Jul 87 19:42:24 GMT-0:04 Dark gray Ok Hardware Light gray Ok Software Red Bad ROM Checksum Green Bad RAM Blue Bad Custom Chips Yellow Exception (INITIALIZATION FROM OS ROMS) Clear Chips Disable DMA and Interrupts Clear the Screen Check the Hardware Pass or fail the Hardware to the Screen (BLUE|BAD) (DarkGray|OK) Checksum the ROMs Pass or fail the ROMs to the Screen (RED|BAD) (LightGray|OK) System setup (..is finished) Check the RAM at $C00000 Move SYS_BASE to $C00000 if it exists RAM Test ; hummm.... not very good though needs to indicate hex location Pass or fail the RAM to the Screen (LED Blinks 9short 1long | GREEN | BAD) Check the Software Pass or fail the Software to the Screen (Yellow|BAD) (LightGray|OK) Set up the RAM Link the Libraries Find External RAM and link it to the list Set up Interrupts and DMA (for boot drive especially) Start default Task Check for 68010, 68020, and 68881 Check for an Exception (System Alert?) System Reset (..Let the good times roll!) --------------------------------------------------------------------------- --------------------------------------------------------------------------- Follows: AmiBugs.txt Summary of symptoms & solutions to common problems on various amiga models --------------------------------------------------------------------------- --------------------------------------------------------------------------- THE FLAKE REPORT "Flaky" (July 15, 1989) Hacker's slang as meaning: 1. Erratic and/or unpredictable behavior or experience 2. Sometimes it works; sometimes it don't 3. Primary cause of the following auditory spasms: a. "ARGH!!!!" b. "AH XXXX..." c. "#@&$!" d. "I need a career change; marketing!" Usage: "He's getting FLAKY..." Means: "RUN! HIDE!" A Bruce's Repair quote: "If it works; it won't." Ok folks, I'm compiling a list of what has caused flaky operation of the Amiga computers. This is a very unpopular subject with Amiga worshippers, but it should be one to pay particular attention since it can harm any product faster than obsolescence and DOES cause untold user-hours of frustrations. Flakiness affects everyone and everything from product development to end-users and especially service. If you can add some more to this list, you can give me a call at (415) 525-6973 and ask for Bruce. I'm busy most of the week so the best time is on Sundays in the morning. If you don't mind listenning to a morning grouch call any other morning. In particular is a problem of poorly designed, slow-to-access RAM boards. This can be especially prominent with fast expansion devices like hard drives and frame grabbers. Number one on the list of bad boards are all those RAM boards with 150 nano-second RAMs. This is the time it takes the RAM to access valid data. The smaller this number the better. There are a lot of Amigas that need modifications. Starting with the A1000's, the daughter board needs to have its PAL chips wired together to the mother board ground and a wire to the expansion bus to the power supply ground connector. In worst cases, two of the PAL chips must be replaced with faster one's. The best source of PALs has been from Spirit Technologies. The A2000's needed to have the keyboard data and clock line capacitors removed. All the Eltek power supplies needed to be checked that a .01 MFD capacitor was installed across R65 to suppress noise and a "00" with a line through it written on the power supply label. The buffer chips U605 and U602 should be 74ALS245 and not the slower 74LS245. A 3300 ohm resistor should be installed between pin #20 and pin #11 on chip U605's address strobe. The Gary chip has been fixed to allow processor access to the KickRoms and expansion devices without needless co-processor contention. (The MOS Gary) The A500 especially needed a piece of cardboard placed behind the keyboard to prevent the keyboard from shorting to the mother board metal shielding. An authorized transistor kludge must be installed on all but the most recent A500's to clean up a signal from the Gary chip. The biggest flake generator was and still is the metal shielding on the A500. The main metal shielding had a lip just behind the internal disk drive (i.e just left of the drive as you face the computer) which does cause shorts at the end of the drive ribbon cable. The solution is to bend the lip under the shielding or to put electrical tap over the edge of the lip. Much can be said about poorly written programs. We've all suffered as unpaid and unwilling "beta testers" from companies lacking in product quality. If it works on their machine, it does not necessarily mean that it will work on all Amigas because of hardware, software, update, and user differences. Sometimes they listen to the problems; sometimes they ignore or pacify us with promises, good-will, and just pure charm. Worst case is the buck passing. Badly written programs can go wild and corrupt our system and even ruin DOS file structures. It can be as subtle as corrupting a single bit, presently unused, to wiping out an entire system. Programs can at times work with no apparent trouble until it's discovered later in time. This can lead to blaming the wrong program or hardware as the cause of the problems. This will sound very cynical but don't believe ANY review or even this report of mine. (sigh..) Just take it with a grain of salt. Look over people's shoulders, get the dealers to demonstrate their wares, stop by a free-form users group and judge for yourself. Seek-out end-users of a product. Get to know the modem community of Amiga users. Report problems to the people responsible for the product if you think you've found a consistent problem. Unfortunately, flaky problems are not easily repeatable nor consistent, so it may be hard for them to justify their time to prove, find, and solve the problem beyond a symptom. Static electricity, even when we don't feel or hear the "tingle", can make computer chips flaky. Always touch the power supply case before even getting close to any circuit board or chip. In the situation of the A500, touch the internal disk drive case. A lot of damage has been caused by AGNUS chip installations. CBM has packaged the computer chips without anti-static material and the retailer many times have not Xeroxed the installation instructions for the customers. Topping the list of user burn-outs is improper cable connections or installation. If you can't bet your wallet, don't do it. I'd say a fair retailer AGNUS installation charge should be around $20-$25. Degrees of unfamiliarity with the equipment or the system can cause unpredictable results. I shutter at the thought of what I would do to my present system if I was a new user and not able to access all the books, documentation, experience, and lastly my fellow computists. An old problem with books, documentation, and advice is that a certain level of background knowledge is expected and assumptions about your system are made from all sides of communication. The learning process is a leap frogging of books, notes, magazines, practice, and many times just pure inquisitive hands-on hacking. Never assume a computer cable is correct if it fits. There are unending variations of cables with the same connectors on the ends. Once you've found the purpose and correct cable, it's best to label the connector ends with where they go. It's always good to have a continuity checker and documentation of the pin assignments. The wrong cable can and does burnout computers. Worst case is if it becomes flaky. Ok, the following is are extracts from my notes and take it with a grain of salt for flavoring. Be careful, because it is in a raw state and reaching a conclusion from the notes will have to be tested for other machines. UNSKILLED AND UNKNOWLEDGEABLE ATTEMPTS AT REPAIR OR MAINTENANCE CAN BE EXTREMELY DANGEROUS AND SHOULD BE LEFT TO QUALIFIED TECHNICIANS ONLY. UNAUTHORIZED SERVICE VOIDS YOUR WARRENTY. All monitors 1) Re-solder HV coil to main board 2) Clean off dust and oil 3) Check for burnt or heated spots 1084 monitor (very similar to 1902A) 1) Intermittents a) Cold solder joints and broken traces especially around daughter boards and HV coil and leads 2) VERY INTERMITTENT "snap!" of video; audibly noticeable. 1084S-Philips (very similar to 1902A) 1) Nothing a) bad R475 (15K 2w flame) damaged from bad C476 (.047uF, 250V) and T402. Between June 88 and Sept 88 require warranty repair. 1084S-P monitor repair kit PN# 314891-01 billed $44 and credited when T402 is returned to parts depot with NARDA form. 1902/2002 monitor 1) Fuse blower a) defective degaussing switch (TH501) b) defective voltage regulator STR30123 (IC501) A500 1) no mouse movements a) replace burnt EMI401 (1.0 ohm 1/4 watt resistor) 2) flaky computer a) do the 2N3906 kludge b) check main computer shield shorting behind disk drive c) Check solder joints on power socket d) flaky internal disk drive power cord e) check for bent chip pins and for bent connector pins f) check keyboard assembly for flakes 3) Power Supply (PN 312503-05) a) pin1 +5V 4.5A b) pin2 shield gnd __ __ c) pin3 +12V 1A |3 \/4 | d) pin4 signal gnd | 5 | Looking into the plug end e) pin5 -12V .1A |2___1_| 4) Green Screen; 10 short 1 long power LED blink a) clean and re-insert Agnus chip 5) flaky keyboard assembly with spurious characters or crash with CAPLOCK LED blink a) replace keyboard and tell customer of possiblity of a serial device being connected to the parallel connector A1000 1) fast steady power LED blink; dark screen a) 74S51 (U9I) & 74F74 (U8I); Damaged from expansion port 2) no parallel output a) 8520 b) PAULA 3) Goes thru diagnostic blinks but no Kick icon a) Check for internal disk drive "track-zeroing" movement 4) Dead a) check that expansion shield fingers aren't bent to mother board 5) Check for bent connector pins 6) no serial a) check MC1488 & MC1489 b) check PAULA 7) Bad mouse or joy stick movements a) check 74LS157 b) check 8520's A2000 (see also A500 & A1000 & A2500 for hints) 1) Red screen; power LED blinks 9 short 1 long continuously a) bad ram with open 2) Dark blank screen on power-up; LED dim a) BUSTER 3) System time erratic a) check for noise on TICK line; CBM modification to power supply 4) Bad mouse movements a) 8520 b) clean mouse c) broken wires in mouse cord d) bad 74LS157 (U202) 5) First character from keyboard missing after power-up a) cut out C910 & C911; CBM modification 6) Fuzzy video a) remove a turn from the ferrite beads on the RGB lines 7) White screen; no Workbench Icon; LED bright a) No power to PAULA; R200 (1 ohm resistor) burnt 8) intermittent guru's a) Bad contacts on BridgeBoard (card edge or chips or bus-timing) b) Virus use KV and Sentry program c) Bad program(s) d) Bad ram expansion board with flaky 150ns ram (should be 100ns); AMIGA 25000 (twenty-five thousand) 2MEG board is FLAKY e) use TestMem by Bruce's repair to find bad bits f) CHECK THE CLOCK SIGNALS with scope for proper voltage levels 9) No Red in RGB only (new unit) a) bad solder joint or bad trace under board at RGB connector 10) Check for bent connector pins 11) No Serial Port a) DTR always on 1) replace MC1488 &/| MC1489 2) bad U301 CIA 3) bad PAULA 12) Modifications: a) Replace U602 and U605 (74LS245) with 74ALS245 Make sure that 74XX24(4|5)'s between Agnus & Ram are F types the symptoms include spots appearing on screen b) Cut-out C910 and C911 c) Put noise by-pass cap (.01ufd) on ElTek power supply TICK line across R65. d) Check for proper usage of ferrite beads at video connector e) put 3300 ohm resistor between #20 & #11 of U605 f) Read TechTopics Issue #25 Section #3 (Apr-May-Jun 89) for details 1) remove R901, C917, C902, C910, C911, C905, C908, C230, C240 2) replace 1.2 KickRom with 1.3 or latest version 3) if U205 & U206 are 74HC244 install RP904, RP905, RP906 (4.7Kx5); if they are not DON'T install (e.g. 74HCT244) 4) add .01 UFD cap on J300 center connector to ground pad 5) add 470 ohm resistor to D800 cathode to second pad from the left, under CN605. 4.3 rev boards and up have R1000 left of Q302 instead. 6) if R5719 installed, add 470 ohm resistor between VCC and CPU side of R106. 7) Replace ALL Gary chips (5719) with MOS type p.n. 318072-01 8) Install new reset chip MITSUMI PST518B into ALL rev 6 boards (see TechTopics 25/3-3.1) 13) Bad joy stick moves a) U202 (74LS157) 14) Garbage from printer port a) bad U300 CIA A2500 (see also A2000 for hints) 1) Put 3.3k ohm pull-up resistors on pin 11, 12, 13, and 14 on U605 These are buffered AS, UDS, LDS, and R/W signals for the expansion A2XXX Power Supply 1) check diodes and all semiconductors with digital IC-safe ohmmeter 2) use variable transformer to bring AC voltage to operation 3) use 25ohm 10 watt resistor on 5v+ main to load for testing Amiga Disk Drives 1) Clean with Q-tips and alcohol a) if heads are sticky when they touch each other, clean heads with "KESTER Rosin Residue Remover". 2) "TICK-TICK" (5 ticks/sec noise with spinning disk in drive) a) after cleaning head and spindle, try lightening the pressure of the head spring (problem especially with #? drives) 3) Works fine when connected as an Amiga Drive but not when connected to a PC Bridgeboard. a) Replace the 74LS38 with a 7438 chip. 4) intermittent operation a) Broken wires in cable; check daughter board interconnects b) cracked magnetic glass switches c) Magnetic interference: rotate drive 90 degrees & recheck d) Motor spin erratic (on-off); re-solder motor board 1) for Matsushita Drives, surface mount chip located between the drive frame and motor board and behind the eject button has bad contact; wedge with spacer 5) Head "plays like a violin" on the disk a) clean head with rosin remover 6) If a cardboard drive protector is used, check drive head mounts and angles. Advise user of the danger of using head protectors from another drive and the possibility of damage to heads with worn protectors bending the head mount springs. 7) If dogs and cats are within fur range, blow into drive openning. Hard Drive Controllers 1) check voltages & cables 2) check bus buffer chips 3) check daughter board interconnects A-Live Board (for A500) 1) With time (hours and moon phase) D#aint## will be missing pixels from its picture when loaded; reloading the same picture with D##### will eventually bring back all the missing pixels! This problem happens when the S#### Harddrive is connected between the A-Live and the A500. Other symptoms include the volume names to WorkBench Screen get corrupted but can be read with the INFO command without error! ) UNSOLVED MYSTERY!! a) Gary chip revision? (How do I get the latest version...) b) Power Supply voltage too low? Too high? c) Bus over-load? d) Needs bus termination? e) Needs F, ALS, or HC type chips buffering between video RAM & Agnus? AMIGA RAM BOARDS 1) A1000 Spirit board a) interconnects broken on Spirit Ram Board b) check for correct shorting blocks and wiring 2) Remove and replace 150NS boards with faster ones. 3) Use Bruce's TestMem to find bad chips Amiga Repair paths: A) Get customer to relate what activity was occurring before the onset of the problem. B) Color of Screen and activity of LEDs 1) Dark screen LED dead or blinking quickly a) Check power supply and TICK line b) Check ALL clocks c) Check power on each individual chip Tips: 1) Bad RAM with an internal OPEN circuit can be checked by "piggy-backing" the ram chip with the same type of RAM 2) Bad RAM with an internal SHORT circuit can be hotter to the touch than the rest of the RAMs 3) Improper removal of chips from sockets with a screwdriver can cut circuit traces under the chip; always check under chips and for damaged socket connections. 5) For the A2000-A2500, put four 3.3K ohm pull up resistors on U605 (74ALS245) a) pin11 to pin20; pin12 to pin20; pin13 to pin20; pin14 to pin20 Tips for Smooth Operation of the Amigas by Bryce Nesbitt & Bruce Takahashi (previously written a couple of years ago) 1) For the Amiga A1000, connect the pin #10's (ground) of the four PAL's together on the daughter board with heavy wire. Apparently the signal ground path is strange and creates unreliable logic signals to U6J, U6K, U6L, and U6N. If you want a better connection, wire the mother board and daughter board grounds together. 2) Check the expansion hold-down screws for proper length (not too long) Sometimes the screw will bend and short the second of the two layers of sheet metal to the circuit board. It may be best to try and first set the screws without the video expansion ram to "pre-tap" the sheet metal. It will be easier then to snug the hold-down screws for the expansion card. 3) Push all chips down fully into sockets. Some chips may not be seated properly or even have bent pins. Straighten bent chip pins with a pair of smooth pliers. 4) Preferences has a screen centering gadget that if moved too far to the left, will cause some of the sprites to be distorted. 5) For programmers: a) Use this instead of AllocMem(): #include "exec/memory.h" /* Safe AllocMem. Will not let your run the system down to zero bytes. * For all to use, by Bryce Nesbitt * * You may wish to increase PANIC_FACTOR. */ #define PANIC_FACTOR_CHIP 4096L APTR SafeAllocMem(size,flags) long size; long flags; { register APTR p; if ( p=(APTR)AllocMem(size, flags) ) { if ( AvailMem(MEMF_CHIP) < PANIC_FACTOR_CHIP ) { FreeMem(p,size); return(0); } /* System is low... no go! */ } return(p); } If you need to tell the user that the system is out of memory, but there is not enough memory to post a requester or Alert, simply set the title of your Window or Screen to "** NO MEMORY **" (possibly with a red pen color). This operation does not require any allocations. b) There is a bug in Text() that will clip text too soon if the write is started from beyond the left edge of the RastPort. c) WindowToFront() (and probably the other Intuition "deferred" actions) will lock up if the user is holding down an icon from the Workbench tool. 6) If you use internal memory expansion, you should ground clip the motherboard to the internal expansion board, preferably at the point on the expansion were the ram array is. 7) Use only high quality disks. Poor disks may format and copy correctly but time may find lost data or files. 8) Make sure that your machine's fan is unobstructed and operating 9) Use a single AC power outlet with enough grounded power sockets for all your equipment. This keeps the AC polarization correct between all your equipment power supplies. If you examine a three prong outlet, you will notice that it looks like a pair of eyes with a mouth. The mouth is supposed to be electrical "ground"; the smaller slot is the "hot"; the larger slot is "neutral". A power plug without a ground prong may have one of its contact blades larger to fit only in the "neutral" slot. Don't ever defeat it's purpose. To do so will endanger you and your equipment. 10) This should have been ICHI BAN: Never connect or disconnect cables while equipment are powered, or blindly probe for a mating. This includes your printer, external drives, modems, and other peripherals. Modems, for instance, have +/- 12 volts on its pins. Damage can result when these pins accidently touch the wrong pins on the computer. Always check to see that you have the appropriate cable and cable adaptions before you attempt usage. 11) Don't guess where the cables connect. Look where you plug your equipment. The A2000 has a round DIN connector for the keyboard. Always make sure the connector marker is on top before plugging. Don't do as many people do. Don't insert and then twist until it fits. This will slowly damage your connectors. IBM PC keyboards are not compatible. 12) Be very careful that the metal band around your mouse connector doesn't short the pins of the mouse port when inserting. 13) If you encounter a power failure, turn-off all your equipment. When power is turned on by your Electric Company, your equipment may experience damaging power spikes or fluctuations. 14) Remove disks when shutting-down a system. Park your harddrive if it is not the auto-parking type. 15) Video monitors develop high levels of static electricity. It is best to plug the monitor and computer into the power outlets before connecting the monitor cable. Always use a 3-prong power outlet. If your monitor plug wasn't designed with a ground prong, use a power outlet that is correctly polarized. 16) Always snug and not tighten the thumbscrews or clips to your connectors. 17) Never place magnets near your monitor. This includes speakers, printers, and telephones which develop magnetic energy. 18) Be sure to include in your startup-sequence file a stack command. However, programmers should check the stack size if they need more than 4000 bytes-Operating System overhead. I *don't* increase my stack, or if I do it's to 8000. (Now you know what me, myself, and I do.) 19) Before working on the interior of your computer, always touch either the disk drive's or power supply's metal casing to discharge any damaging static electricity. 20) The Amiga monitors have a metal shield installed under the casing. If you are using a non-Amiga monitor, make sure that your monitor has some shielding or make one using a metal kitchen tray (?). 21) Don't mix and blend versions of operating systems. You are asking for problems and will get them most of the time. If you are still using older software, you are asking for problems anyway. 22) When paying for shareware and you want a response from them, cut the bill in half and staple a note as to where the other half went. Nah, don't do it; it's illegal. Darn my buckies! I just became a felon when I thought of an excellent programmer. 23) When plugging in cards for the A2000 Amiga, there is the end of the card which screws to the back of the Amiga. The metal bracket, which is attached to the card for this purpose, has a tendency to catch at the bottom of the bracket to the casing of the Amiga. To seat properly, the bracket must be pushed against the back of the Amiga and then it will move further down. Make sense? The main point is: Don't force the bracket to seat and especially don't use the screw to force it to seat! Always screw the cards down to prevent shorts 24) Genlock for the Amiga may need some modifications to sync properly. The modification needs to be done on the early models and requires that R55 resistor be removed and R108 to be changed to 1.5K ohms. R55 is a 4.7K ohm resistor located near the Q3 transistor, and R108 is a 1K ohm resistor located near pin#10 of the MC1377 chip. 25) The composite video of the Amiga A1000 needs color correction. Your red, greens, and blues may not look correct. The modification is simple; just remove resistor R140; located on the rear-left of the motherboard. On some A1000's, R140 will have to be replaced with a 470K ohm resistor instead. 26) CORRECTED! 27) Keep your equipment out of sunlight; even when reflected by mirror or walls while you are away from home. Overheating problems are increased if the power supply vents are blocked or if it is resting on a rug. Keep the power supply in a well ventilated area. 28) You cannot keep your cat or dog's fur out of your internal disk drive. The fan sucks through there. Internal drives now have spring loaded doors on the front which help in reducing contamination. 29) A clean mouse is a healthy mouse. Clean your ball and rollers with Q- Tips, rags, toothpicks, picks, and jack-hammers. 30) Sticky keyboard keys? Remove that key button with a chip puller and clean both button and switch with Q-Tips and alcohol. If your lucky, the shank of the key switch isn't split. If it is, The split will widen in the switch and wedge. Replace the switch or oil the shank with 3in1 oil only. You may get lucky and find a repair station with some damaged keyboards with good switches. 31) Does your monitor seem to sink into your A1000 computer case? Put a plywood or 1/4 inch plexi-glass platform underneath. Does your A2000 keyboard seem to sink in the middle? Re-enforce the middle of the keyboard's circuit board with a rubber spacer. Does this list seem a bit long? Make some hot apple cider and come back here. 32) If one or more of your mouse buttons goes flaky, it can be replaced. If the switch is "Flag", with a square body about 12mm in size with four leads you may be in luck. If the switch is the type where the actuator is completely flush to the switch body, the replacement part can be had from Panasonic; Digi-Key (1-800-DIGI-KEY) sells it as part #P9950, 36 cents each. If the switch button is slightly raised from the main body (by about 1mm) you will either need to adapt the above part or try and find a better match. Mouser electronics (817-483-4422 or 619-49-2222) part # 10KB001, 49 cents each, *might* do the job. Some mice switches are dual switches with only half being used! Use the other half by rotating the switch 180 degrees. 33) GET MEMWATCH from John Toebes!! 34) CORRECTED! 35) Dead Issue. 36) Ribbon cables should never be bent at angles to the degree of being sharply folded. All folds of ribbon cable should gently loop. A sharp crease can damage, short or break the wires inside the ribbon cable. In the cable from the disk drive mechanism, this can mean Guru's or the device not being recognized. MANY RIBBON CABLES FOR THE BRIDGECARD HAVE BEEN DAMAGED BECAUSE OF THE CREASES IN THE PACKAGING OF THE PRODUCT. THIS HAS DAMAGED DRIVES AND BRIDGECARDS. IF A RIBBON CABLE IS SHARPLY FOLDED, USE AT YOUR OWN RISK. 37) Copy and run questionable or unknown programs in RAM disk with your disks removed or write protected. This will prevent you from crashing the disk drives and damaging the disks. 38) Corrected! 39) For A2000 users with BridgeCards, keep the ribbon cable going to the 5 1/4 floppy away from the motherboard. Lay the ribbon cable on top of the cards instead of underneath. The ribbon cable picks up interference which can cause your machine to intermittently GURU or cause devices not to be recognized. (*** note *** Some A2286 bridgeboards will display parity errors. Return these for exchange.) 40) All computer equipment need a minimum amount of time before powering back on-line. For the Amiga A1000 and A500, you must wait a minimum of 20 seconds before power-up and as long as 30 seconds or more for the A2000 Amiga. Computers need time to completely power-down and discharge all voltages which may be sustaining corrupted data in RAM and other chips. 41) If your computer monitor remains powered and unattended for extended periods of time, use a display blanking program. This type of program will "black-out" your display until there is some kind of user action from the mouse or keyboard. Your display will temporarily "black-out" after a set number of minutes of inactivity. Public domain programs like "PopCLI" from the Software Distillery and "ScreenSaver" from Perry Kivolowitz are good examples. Leaving the colors stationary for days on end will burn-out the phosphors of the monitor leaving you with a ghost image of the display forever. I set my screen to black-out after 10 minutes of inactivity. 42) It's a good idea to assign your T: directory to RAM:T before executing any command script. The reason is increased speed and less drive activity. --------------------------------------------------------------------------- --------------------------------------------------------------------------- Follows: A500Fix.txt Summary of symptoms & hardware reapir solutions to common problems on the a500 + various amiga models --------------------------------------------------------------------------- --------------------------------------------------------------------------- -= A DIY Guide to Computer Repair & Modification (PC and Amiga 500) =- -=<* About This Document - Disclaimer *>=- This document is intended to provide electronics hobbyists with some useful notes the author has gathered whilst working on various systems. It is not intended to train or encourage novices to attempt service or modifications to expensive appliances. It is especially not intended to encourage unqualified personnel to tamper with dangerous appliances such as monitors, power supplies and other devices which contain vacuum tubes, live mains or high-tension rails, or other hazardous areas. Any such work carried out is done at the reader's own risk and the author accepts no reponsibility for damage to property or person which occurs as a result of attempting any of the procedures described herein. Having said that, I can vouch for the workability of the modifications listed here. I have personally performed them all myself on my own machines (this is, after all, a chronicle of my own experiences, chopped up under suitable headings for your convenience). With regards to the service information, whilst I have described problems and the solution(s) I found, keep in mind that this is rather like a doctor prescribing medication over the telephone or from an encyclopaedia. What I mean by this statement is that different problems may well cause the same symptoms; to take a trivial example, if you turn your monitor on and nothing happens, perhaps the fuse is blown, but on the other hand, perhaps it is not plugged in, or perhaps there is a more sinister fault in the power supply section. For this reason, I suggest you use the service information as a very vague guide ONLY. Remember; it is very rare to find two machines which are exactly the same inside, and so what I have found to be a suitable solution to a given fault may be totally inappropriate to your situation. -=<* The Commodore Amiga 500 *>=- i. Serial Killer ---------------- Problems with Amiga serial ports generally fall into three categories; problems with the flow control lines, problems with the actual data transmission lines, and problems with the line level (caused by faulty line driver chips). The first two can be relatively costly to repair, due to Commodore's monopoly on the CIA and Paula chips, so I advise exploring the line driver section of the circuit before rushing out to buy new Paulas or CIAs. Faults in the line driver chips (MC1488 and MC1489, U38 and U39 respectively in the schematic on page F-7 of the book 'Introduction to the Commodore Amiga 500') are typified by either total loss of transmission, total loss of reception, or both. If you look at the flow control lines, (CTS and RTS), you usually see that these lines are behaving normally (exactly why these lines are rarely affected is a mystery to me); if not, then you probably have a faulty CIA. Since the 1488 and 1489 only cost around A$1.00 each, depending on your source, it is well worth replacing these chips before you investigate Paula. Unfortunately, they are not socketed so you will have to desolder them (see "Desoldering Small IC's" below). When you have the chips out, put in a couple of sockets to facilitate later repairs. If, after replacing the 148x's, you still experience problems, it is time to look further. If you have suitable software, you can check whether the problem lies in the flow control lines (in which case you have a damaged even CIA, U8) or in the data lines (in which case you have a damaged Paula). If you do not have, or are unable to interpret the results of, this software, you can make use of an old Amiga-tech wrinkle; exchange the CIA chips and see if your fault clears up. If it does, then ten to one the problem is in the CIA which started out as U8; if the problem persists, then it is most likely a Paula fault. ii. Floppy Hassles ------------------ In my life I have opened at least 40 Amiga 500's and have NEVER seen two which have the same make and model of internal floppy. It seems that Commodore change their suppliers (and also the colors of the LEDs on the keyboard) on a weekly basis. Let's see.. three possible LED colors (red, green, yellow), three LEDs on the keyboard, four floppy manufacturers (Sankyo, Chinon, Panasonic, Sony), two different styles of head connector (one film connector per head or one wide film connector servicing both heads), helical screw or belt-drive head carriage mechanisms.. that makes 144 possible configurations already. For this reason it is not possible to give specific "look-to-the-left- of-the-large-chip" directions, and I can only state a couple of possible faults and their possible causes : * Floppy refuses to acknowledge disk insert Probably caused by a defective odd CIA (U7). Try switching the CIAs over. Also check that the switches at the front of the drive travel freely up and down. Verify that the pads to which the switch assembly is connected have not flaked off the board (this can be caused by rough disk insertion). * Floppy will not read disks formatted in other drives The head alignment is faulty. There is a method of adjusting it without special tools and measurement devices, but it requires considerable patience and one of the X-Copy series of programs. The method is as follows : - Format a disk in a working drive. - Open your machine (or external drive). Remove the cover from the drive unit (it is usually held on by one screw on either side and another on top at the back). Locate the track zero sensor and loosen the screw which holds it in position. Load X-Copy and select the Toolkit option CHECKDISK. - You must now align the lower head. This can be accomplished by moving the track zero sensor a little, then checking the disk, and repeating this until you find a position in which the drive will read the lower side of the disk. When this is done, tighten the screw which holds the track zero sensor, to stop it shifting. If you have any Lok-Tite, a drop of that on the screw is advisable. - You must now align the upper head. Loosen the two screws which hold it to the head carriage assembly (Do NOT remove these screws, unless you relish the idea of going over the floor with a metal detector looking for small springs). Adjust the upper head by eye until it appears to be exactly over the lower head. Now repeat the above trial-and-error process, tweaking the upper head around until you find a workable position. Tighten the screws, replace the cover and reassemble. If the above procedure sounds rigmarolish and uncertain, it is ! But I have successfully performed it on a number of Amiga and PC 3.5" drives. And I have never had a failure with it. iii. Caps Lock Chaos -------------------- Many Amiga owners will know, to their detriment, that occasionally the Caps Lock light will start blinking and the keyboard will lock up. This is caused by the microprocessor in the keyboard detecting a keyboard fault. I first noticed this fault when our school Amiga room (two rev. 5a A500's) acquired an autofire joystick, a Quickshot IIb I think. When switched to autofire mode, this joystick would periodically jam the keyboard. If you have recently acquired an autofire joystick, you should investigate whether turning it off during boot fixes the problem. Otherwise, you can try the old "Atari Twist", ie pick up your machine in both hands and twist it. This is basically equivalent to reseating the chips on the motherboard; if you have a spare moment, I suggest you actually open the machine up and manually reseat them. iv. Bulimia of the Agnus ------------------------ iv-1. What is the 1Mb Agnus ? ----------------------------- The 1Mb Agnus (variously known as the Obese Agnus or Fatter Agnus), Commodore part 8372a or 318069-02, is the relatively new Agnus which is capable of addressing 1Mb of chip-RAM. This allows you to have twice the amount of sampled music, screens, and other custom-chip data in memory simultaneously. It also has the desirable effect of letting you run things like Deluxe Paint in 16-color 640x512 (or 640x400, NTSC users) mode, without having to disconnect external drives, close down WorkBench screens and the like. For A-Max users, installing the new Agnus and configuring it to 1Mb chip-RAM mode will also increase A-Max compatibility. If you have more than 1Mb of RAM, then it will make A-Max virtually 100% identical to a Mac Plus, memory-map-wise. NOTE WELL : This modification requires 1Mb of RAM to be visible ! Commodore, not wishing to make two chips where one will do, is now shipping the 8372a in most (nearly all Rev. 6a) A500's, without telling anybody. In these machines, the extra chip-RAM capability has been disabled so that if you connect an A501, it will still think it is "slow" [see below] RAM. iv-2. An Aside on Memory Speeds ------------------------------- The Amiga has *three* types of RAM. Chip-RAM, Fast-RAM and "Slow"-RAM. Contrary to what many people assert, RAM at $C00000 (the default location of the A501 expander, and the second 512K of RAM in A2000's) is NOT fast-RAM, even though the system reports it as such. Because this RAM is refreshed and accessed via Agnus, it is affected by buss contention in just the same way as chip-RAM. It is simply a dead area in RAM which is not accessed by the custom chips and which is not faster than chip-RAM. Moving this RAM to $80000 (which is what you do to enable 1Mb chip-RAM) will have no effect on machine speed at all. iv-3. Compatibility ------------------- To date (20-Oct-91, 18:11EST) I have personally tested at least 400 pieces of software with the new Agnus. I have found three programs which do not work : * Double Dragon II (Completely screwed up) * VideoFX 3D (Again, completely useless) * Impossible Mission II (This game requires memory at $C00000. It does not mind the Agnus, but if you want to run it you must drop back to 512K chip/512K slow mode. Lousy AllocAbs() programmer !) In addition, Dragon Ninja thinks you are running on a 512K machine and will not play in-game music. Again, this can be rectified by switching into 512K chip/512K slow mode. Some other games also think they are running on a 512K machine, notably TechnoCop and R-Type, but this is of no real consequence. iv-4. Identifying the Version of your A500 ------------------------------------------ There are several versions of the A500 out there. I have only tried fitting the new Agnus to the following : a. The Revision 5 board shipped until early 1989 b. The new Revision 6a board supplied from May (?) 1989 onwards The way to identify your machine type is to check the expansion port which lurks under a plastic cover on the left-hand side of the computer. The Rev. 5 machine has a very fat strip (double width) at the back of the connector; the Rev. 6a board has two normal-width strips instead. iv-5. Installing the 8372a to Revision 5 A500's ----------------------------------------------- 1. Remove the 8371 from its socket. If you are an NTSC user who does not wish to use the PAL mode, go to step 3. 2. Pin 41 of the new Agnus controls whether the machine starts up in PAL or NTSC modes. When it is tied low (to ground), the machine boots in NTSC mode. When the line is tied high or left floating (ie unconnected), it boots into PAL mode. On the Rev. 5 board, pin 41 is connected to ground by tracks on BOTH sides of the board, making it virtually impossible to cut the track without desoldering the socket. This means if you just plug in the new Agnus, you will be locked in NTSC mode !! There are a couple of ways to go about circumventing this problem; I will detail here the one I undertook on my own Rev. 5 board. I will assume you want to install some sort of switch to toggle PAL/NTSC mode. If you only want to run in PAL mode, you can simply bend out pin 41 of the Agnus socket (don't bend the pin on the chip) to prevent it from making contact with Agnus. If you do this, proceed to step 3. Otherwise, get yourself an SPDT or SPST toggle switch and two lengths of telephone (or other thin, stiff single-core wire). Solder wires to the switch : +---+ To a convenient ground--+-o | BACK VIEW OF SWITCH +--------+-o | When held as shown, UP=PAL, DOWN=NTSC. | | o | | +---+ Uninsulated --> | | <-- This side is insulated \-/ <-- Fold the wire thru 180 degrees 3. Insert the new Agnus. If installing the switch, you should now poke the loose end of wire (see above) from the switch into pin 41 of the socket so that the bare copper side touches the pin on the chip and the insulated side touches the pin on the socket. In order to fit the wire down the hole you may find it necessary to bend out or remove entirely [Not recommended !] the pin on the socket. Secure the wire with a tiny drop of cyanoacrylate adhesive. 4. If you wish to install a memory mode switch, go to step 5. Otherwise, locate JP2 (between 68000 and ROM). This consists of three pads. The center and lower pads are joined by a thin track. Cut this track and place a drop of solder between the center and upper pads. Now locate the _EXRAM line coming from the A501 port (it comes from pin #32 and runs on the upper side of the motherboard parallel to the A501 connector). Cut this line. You have now completed the installation procedure. 5. Complicated. Locate JP2 and cut the track which joins the center and lower pads. Locate the _EXRAM line from the A501 port (see step 4) and cut the track. Solder wires to all three pads of JP2 and one wire to either side of the gap you cut in the _EXRAM track. Wire a DPDT switch as follows : +-----+ BACK VIEW OF SWITCH Upper pad of JP2 --+-o o | When held as shown, UP=512K CHIP, DOWN=1M CHIP Center pad of JP2 -+-o o-+- To one side of the gap in the _EXRAM track Lower pad of JP2 --+-o o-+- To the other side of the gap +-----+ You have now completed the installation procedure. iv-6. Installing the 8372a to Revision 6a A500's ------------------------------------------------ 1. Remove the 8371 from its socket. Insert the new 8372a. NTSC users who do not wish to use the PAL mode should go to step 3. When installing the new Agnus, note that on the 6a board, the Agnus socket has been rotated 90 degrees anti-clockwise from the orientation on the revision 5 board. For this reason, plugging in the Agnus correctly is no longer an intuitive operation ! 2. JP4 controls PAL/NTSC video mode. If you are in North America or Hong Kong or anywhere else the National Television Standards Committee TV format is used, this should be bridged by a track or a blob of solder. If you are in Australia, Europe or anywhere else the Phase-Alternated Linescan TV format is used, this jumper should be cut open. If you wish to install a switch, then simply connect it across the two pads of the jumper. 3. Cut the track joining the center and upper pads of JP2, and the track joining the center and upper pads of JP7a. (JP2 is between the CPU and the ROM and JP7a is just to the left of the A501 connector). If you wish to install a memory switch, proceed to step 4 otherwise solder the center and lower pads of JP2 together. You have now completed the installation procedure. 4. Connect a DPDT switch as follows : +-----+ BACK VIEW OF SWITCH Upper pad of JP2 --+-o o | When held as shown, UP=512K CHIP, DOWN=1M CHIP Center pad of JP2 -+-o o-+-- Center pad of JP7a Lower pad of JP2 --+-o o-+-- Upper pad of JP7a +-----+ You have now completed the installation procedure. v. Is My Jumper On The Line ? ------------------------------ Number Rev5 ? Rev6a ? Function ------------------------------------------------------------------------------- JP1 yes yes Connects reset timer (NE555) to main reset JP2 yes yes Maps A501 at $C00000 or $80000 JP3 yes yes Swaps _CAS of RAM banks (of use for test purposes) JP4 no yes 8371 Agnus : TEST line [solder closed !!] 8372a Agnus : PAL/NTSC video mode select JP5 no yes 28MHz base clock to Agnus JP6 no yes 7MHz clock on pin 7 of expansion connector JP7a no yes Controls _EXRAM to Gary JP7b no yes CIA tick from VSYNC or pin 32 of A501 (default VSYNC) JP8 no yes LPEN from FIRE0 or FIRE1 JP9 no no ??? A non-existent jumper. Future Rev. 7 ??? JP10a no yes Connects AUDIN to pin 18 of serial port JP10b no yes Connects AUDOUT to pin 11 of RS232 port JP11 no yes Connects CSYNC to BCSYNC or video hybrid ------------------------------------------------------------------------------- NB: These are A500 jumpers only. A2000, 2500, 3000 have different jumper assignments. The 1000 *may* have similar settings but I cannot guarantee this. vi. Hol(e)y, Hol(e)y, Hol(e)y ----------------------------- Owners of Rev. 6a A500's will notice that they only have 4 RAM chips as opposed to the 16 in the Rev. 5 and earlier machines. They will also note that in between the RAM chips are empty sets of holes which look like something ought to go into them. Firstly, fear not - the reason you have a quarter the number of RAM chips as older machines is that the 6a uses 44256 4-bit x 256K chips which are four times as large as the 41256 1-bit x 256K chips used in the 5 and earlier revisions. All the modern Amiga memory hardware (except possibly the A501) uses these larger chips because they are slightly cheaper on a dollar-per- megabyte basis. For example, the older Series I A590 hard drives use the 41256, and they will accept up to 2Mb. The new Series II A590's use the 44256 (and consequently have enough space to fit 8Mb of RAM). But, back to those extra holes. They are indeed designed to accept something; viz, another set of four 44256's to take your machine up to 1Mb without having to buy an A501 or other expander (this is particularly useful if you have a memory expansion which uses the A501 slot, and you want to have 1Mb chip-RAM). If you want to install your own RAM there, you should do as follows : Purchase four 20-pin IC sockets (preferably machined-pin). Make sure you have a solder-sniffer. Now look at those holes and you will see that they are clogged by solder (this is due to the way the boards are soldered; the process covers all exposed copper areas with solder). You must clean this solder out by heating the board from one side and sniffing the solder out on the other (or blowing the solder through; if you choose this method, make sure to remove all the little splashes of solder from the board and your lap). When you have cleaned out all the holes, solder in the sockets. Now plug in four 44256 chips and you have 1Mb of memory for slightly less than the cost of an A501 (in Australia, the difference is roughly A$20). With respect to the speed of RAM chips required, I use 150ns chips with no problems at all; however, I suspect that Commodore would recommend 100ns devices. The price difference is minimal so you may as well buy 100ns chips so that if you ever buy a series II A590, you can shift the chips over and have 100%-guaranteed-not-to-overheat fast-RAM. vii. 1Mb of Motherboard Memory on the Rev. 5 -------------------------------------------- It is possible to install 1Mb of RAM onto the revision 5 motherboard. However, this modification is flaky at best and I cannot recommend it (having tried it in a moment of sheer boredom). Also note that I could *not* get this extra memory to be mapped at $C00000 (the computer would only recognise it if I had JP2 set to map the A501 at $80000); which means that it is only of potential interest to owners of the 1MB Agnus. (This failure to work as $C0 RAM may well have been due to some stupid omission on my part). I will deliberately be vague because this is not a trivial modification. If you are unable to work out what to do with confidence, you do not have enough knowledge to perform the mod. The procedure can be summarised as follows: Take sixteen 41256 RAM chips (for speed information, see the end of subsection vi. above). Bend the refresh address strobe pins (_RAS, pin 4) on all the chips up and over so that it is well clear of the other pins and easily accessible from the top of the chip. Bend in all the other pins a little. Now, piggyback the new chips on top of the existing RAM, making sure to install them in the same orientation as the original chips. It is not possible to reach all the pins to solder them, so you will have to content yourself with only soldering the corner pins. Solder wires from the bent-up _RAS pins to pin #38 of the A501 port (or any convenient take-off point of this signal). You should now have 1Mb of RAM. (If you want to try using it as $C00000 RAM, you should ground the _EXRAM pin, pin #32, of the A501 port. I had no success with this). This mod sounds all very well, but in the current climate it may be slightly cheaper to buy a secondhand A501 than to buy 41256 chips. In addition, due to the precarious hold the piggybacked chips have on the originals (because there isn't enough room to solder all of the pins down), the mod is sensitive to shock; if you tap the table, you can sometimes guru the machine. For this reason, this is a "possible but ill-advised" modification. viii. Double Trouble -------------------- The hack to accelerate your Amiga to 14MHz has been published in countless articles, but I may as well include a brief description of it here. The hack involves removing the original 68000 from your Amiga and substituting a version rated at 16MHz (confusingly called the 68000P-12; the Motorola chips have "16MHz" stamped on them, but the SGS-Thompson clones do not). The clock pin is bent out and soldered to the output of a divide-by-2 counter whose input is connected to the base 28MHz clock. THIS MODIFICATION SHOULD BE INSTALLED WITH A SWITCH !! If not, you WILL (not may) find that some games will refuse to load because they use timing-dependent loaders. Aside from the problem mentioned above, the only compatibility down-side to this modification is that some floppy drives will not handle the increased step rate. If you find that your drives give read/write errors at the high speed, you can either replace them or run a program called "DFDelay" to slow down the step rate. (If df0: will not work, you have a problem. Try swapping df1: for df0: - to do which you will need a Commodore df1:. The mechanisms used in the old A1010 drives are EXTREMELY reliable and much quieter than the new rubbishy things; if you have an A1010, you can be fairly certain that it will support the new speed). To perform the mod, remove your old 68000 and embed it in a perspex block for future reference. Now rig half of a 74S74 dual D bistable as a divide-by-2 counter. Connect the input of this to a convenient take-off point of the 28MHz clock line on the motherboard (I use pin #34 of Agnus, but anywhere will do). Now bend out pin 15 of the new CPU and solder a wire to this pin. Take a piece of stiff telephone wire, strip approx. 5mm of insulation from one end, and stick this end down pin 15 of the 68000 socket. Insert the new CPU in the socket and verify that pin 15 is well clear of the wire in the socket. Now wire a SPDT switch as follows : BACK VIEW +---+ When held as shown UP=7.14MHz, To output of divide-by-2 counter -+-o | DOWN=14.28MHz To pin 15 of 68000 -+-o | To wire in pin 15 of 68000 socket -+-o | +---+ The 74S74 should be mounted somewhere convenient; I break off all the unused pins, bend the remaining pins out, and stick the chip on top of one of the data path IC's; this has the advantage of allowing me to take power directly off the existing components rather than stringing yet another pair of wires through the machine. If you only have chip and/or slow memory (see subsubsection iv-2.) then your machine will run at approximately 150% normal speed (on CPU-intensive operations; DMA rates will be unchanged). If you have true fast-RAM then code running from fast-RAM will execute at close to 200% of normal speed. Try placing a large perpective brush with anti-aliasing HIGH in DeluxePaint III (or IV !) and you will see the speed increase. ix. The Numbers Game -------------------- This is how PLCC chips are numbered (using Agnus as an example) : 1 1 8 8 8 8 8 7 7 7 7 7 1 0 9 8 7 6 5 4 3 2 1 4 3 2 1 0 9 8 7 6 5 BEVELED CORNER | | | | | | | | | | | | | | | | | | | | | /-------------------------------------------| 12 -| o |- 74 13 -| |- 73 14 -| |- 72 15 -| |- 71 16 -| |- 70 17 -| |- 69 18 -| |- 68 19 -| |- 67 20 -| 8372A |- 66 21 -| |- 65 22 -| |- 64 23 -| TOP VIEW |- 63 24 -| |- 62 25 -| |- 61 26 -| |- 60 27 -| |- 59 28 -| |- 58 29 -| |- 57 30 -| |- 56 31 -| |- 55 32 -| |- 54 |____________________________________________| | | | | | | | | | | | | | | | | | | | | | 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 x. A Change Of Face ------------------- Installing the ECS Denise is simplicity itself. Simply remove the old Denise and plug the new one straight in. Note that to use the new video modes, you require the 1Mb Agnus (not necessarily in 1Mb chip-RAM mode, though). By installing the new Denise, you also eliminate the annoying video glitches which occur in NTSC mode when using the new Agnus with the old Denise. xi. Snap, Crackle and Pop ------------------------- [For non-Australians, the above is the slogan a local cereal company uses to advertise a tasteless soggy mess called Rice Bubbles]. Symptom : Your monitor produces snapping or popping noises, and sometimes goes unaccountably blank after being switched on for a while. I have no idea why this problem seems to affect Commodore monitors so badly. It is caused by arcing of the EHT rail (around 14kV, from memory) to lower-voltage areas of the set. Initial treatment is to turn off the monitor, leave it for a couple of days (to allow capacitors to discharge), and then to remove every last speck of dust from the inside. This usually works. If it does not, however, sterner measures are called for. Open your monitor and (here comes the dangerous part) leave it running, open, for a few hours. If you actively work against Murphy's Law by watching it from behind something or inside something, where the monitor can't see you, you MAY eventually be lucky enough to actually catch it in the act of arcing. Mark the place with a spirit pen and spray on some anti-gaussing compound. (This stuff has a very high dielectric constant and hence helps to prevent arcs). xii. Yo Ho Ho And A Packet Of Disks ----------------------------------- I sometimes describe A-Max as the only useful productivity tool for the Amiga; Mac owners will agree with me when I say that Macintosh applications are incomparably better than their Amiga counterparts. However, due to suppression of the source of 128K ROMs by a certain computer mega-corporation named after a piece of dead plant, the future of this marvellous product looks slightly less certain than Melbourne hosting the 1996 Olympic Games (grin). There exists a software patch which will allow you to [illegally] run the emulator using a ROM image file on disk; however, if you wish to use a Mac drive with the A-Max cartridge, you must have ROMs or EPROMs in the ROM sockets. Problem ? No. Simply insert two blank 27512 64K x 8 EPROMs in the ROM sockets. NB: The above procedure is wholly illegal and the author is not explicitly condoning nor advocating the practise. I personally own original Apple 128K ROMs (purchased before the great ROM drought). The above information is supplied for interest's sake only. ======================================= THIS TEXTFILE BROUGHT TO YOU BY: MATRIX =======================================