Amiga 4000 Hardware

Here I will try to collect different hardwareproblems and their solutions.  This is a “never to be finished page” and have no idea whatsoever if this is a good media to do it. But. ok let’s try. ok?

Some fixes and troubleshooting will require you to have spares, oscilloscopes, hotairstation, solderstation etc. and know how to use it. if not: let someone who got the knowledge/stuff to do it.


First something really important: Schematics

For the most usual version of the Amiga 4000: A4000_Rb_schematic

For the Cost Reduced version with onboard 030 on the motherboard: A4000CR_Rd_schematic

And for the 3640 68040 CPU Board: A3640_R3_schematic


The first thing you must check is: BATTERY, BATTERY, BATTERY.

MANY MANY Amigas are thrown away due to leaking batterys. if you have a barrel-battery.  change it.  or even better CUT IT OFF! if you really need a battery, get another solution, coincell or so.  or solder in wires and place the battery FAR AWAY from the motheboard. (there are space in the front)

So check around the battery, if you see ANY KIND of traces of green/blue stuff. clean it up with isopropanol, then clean with lemonjuice and then again isopropanol.

there are a section below handling battery-leakage problems.

Then check your caps.  from factory there are 2 caps mounted the wrong way around the audioports. C443 and C433 this will make them more eager to “leak”  but check ALL caps.  the pins to the caps should be shiny. if you see any kind if greenish/brownish stuff around it: RECAP.

BUT much people thinks that recaping solves all Amiga problems: this is not true. Actually the Amiga 4000 boots without any of the electrolytecaps. (but unstable).   but ok. dead shorting caps is not good. but recapping is NOT a final-solution for all problems.




Green Screen, Powerled flashes:

Green screen means that chipmem is not writeable. ATALL. (your machine can still boot if the upper part of chipmem is dead.. but when lower part is, this will happen)

mostly your chipmem simm is not seated correctly, or broke (or simmsocket).  check with another simm. even 4, 8MB simms works. (but will give like 1 or 2MB chipmem. you will NOT get anything more)

( BUT hey. the J213 says 8MB.  This is the “Free sex and beer” jumper. IT WILL NOT WORK. .EVER OK? this was for testing newer chipsets, never released. there are no hack to fix it. the AGA chipset cannot adress more then 2MB of memory. )

Check traces and vias, any green stuff? maybe batteryleakage damaged traces on the board?

I have noticed a bad U208 on hte A3640 040 card can also result in a green screen.

On machines with batteryleakage. a very damaged U177 can result in a green screen aswell.

Black Screen, nothing happens:

First check the powerled: when you start up the machine, the powerled is not in full brightness and it will change after 1-2 seconds. IF this happens, your cpu is working as it has been able to pass it’s first steps in its startup-process.

Just to test: remove chipmem, green screen? your CPU seems to be working. ROMs seems to be working.
(as that test IS in rom and needs a cpu to run. 🙂 ) insert chipmem again.


Brightness does NOT change:

First of all. the Amiga is a very old machine.check that everything is in place. aslo clean CPU board connections with isopropanol and a (not used) toothbrush. and check that all socketed ICs are in its sockets. (ROM, some Busters etc)

ROM ICs dead/Wrong socket: check that you have the correct ROM in the correct socket. also, try different ROMs. You MUST have A4000 roms.

Check clocksignals in an oscilloscope, Like SCLK generated by LISA (pin 22). if SCLK is not generated it might be U975 that is faulty as it generates MDAT that is required for LISA. os if MDAT is low, no SCLK will be generated meaning no boot.  U975 is often affected by batteryleakage.


Brightness DOES change:

OK. Your CPU is working. atleast so much so it can do the first parts of systemtests.

To test: press Caps Lock MANY MANY times. (20-30?) the capslock led should go on/off at all times, if it gets stuck your cpu are unable to empty the buffer from the keyboard MPU. So most likley your machine crashed. (CPU)



 Batteryleakage problems:

This is one of the hardest problems. but we try.

Red Screen during boot: This is a kickstart error. Check U891 if all connections are good. also check ground and power. often affected by batteryleakage.

Dead mouse: Some boards with heavy batteryleakage have a dead mouse (mouse buttons are working) check and change U975 and U976, they are 74HCT166. And it seems to be a common issue that they simply die due to the batteryleakage.

U177 is also very often affected.  meaning that RTC will die. or actually “green screen” aswell

Missing Fastmem.

First the obvoius, test other SIMMs, the sockets are also very bad, are SIMMs seated and then also check traces, batteryleakage can kill traces.
but if you have checked it all and still no fastmem.
Start your machine and start some kind of memoryedit tool lite asmone etc. check memory at $7f00000 this is the first SIMM module (4MB)  fill with 00 00 00 00 00 00 etc. re-read the memory: looks ok?  then fill with FF FF FF FF, still ok?  well fill with different patterns. and check if it is ok.  if so?  Don’t know. memory should work.

but if you instead of 00 00 00 00 get  00 00 00 FF  or instead of FF FF FF FF you get FF FF FF 7F or so. you have a problem.  you have some 74F245 that buffers the memory.  U891 is located close to the battery and will easly be damaged by batteryleakage.  AND..  guess what  U891 handles the last 4 bytes in the longword..  00 00 00 FF  means you have problems with U891.   00 00 FF 00 is U892, 00 FF 00 00 is U893  and FF 00 00 00 is U894.

check traces or replace the ICs.




22 thoughts on “Amiga 4000 Hardware

  1. Thank you this is useful 🙂 i have one machine with a nasty problem i can’t fix, black screen and power led flash about 10 times, then it reboot, this behaviour continue endless, absolutely no battery damage. tried different simms for chipmeme, and various/no simms for fastmem, but no luck.. any help please?

    1. Try without fastmem, do you see a green screen? or still black?
      in cases like this I use the Logica Diagnostic rom and see if it statrs up. then test 8520s..

  2. I’m trying to bring back an A4000T motherboard to life. The board was working shortly before.
    So far measured out the clock signals, RESET on all custom chips and MDAT lines and all seem OK, yet the board behaves as if no CPU card is present (no grey screen is generated). Any tips on what signals to check further? All obvious things are checked already (contacts, correct supply voltages, A/V and CPU boards, burned or overheating components, physical damage)

    1. no.. actually have the exact the same situation with a board here now. hope to get time really soon to check more about what signals to check.

      does powerled go from semibright to full bright? that is the first thing to check, then you know cpu is started up.

      1. I had an A4000T that got more and more unstable, and then died. after spending time and money getting the board checked out, it turns out that the PC/AT type power supply – the power supply connecter to the A4kT mobo had *burnt through* on the 5 volt lines! it was only when I looked at the power plugs from the power supply and wondered why the plastic looked like it had bubbled I ran a multimeter on it and there was no +5volt getting to the machine.
        it was a fully loaded system and once I figured this out, I fed it a new PSU about once every couple of years, and it was happy.

        are you getting a caps lock light? if the CPU is dead or with no CPU board, you should be able to power on and mash that caps key. if the capslock light stops switching after a few seconds, then cpu issues. If the cpu is ok, the keyboard asic will keep toggling the caps lock light for as long as you keep pressing that key.

        otherwise, clean that cpu slot on both the mobo and the cpu card. it’s a know black spot. and black screen is no CPU detected. i’m about to send a fully dead A4k mobo off to amigakit to see what they can do. not even got a power light :'(

        so, what’s your power light doing, and is your keyboard caps lock light flashing when you hit it, or is it doing it’s own flash dance?

        1. Black light can also depend on so much other then “no cpu detected” damaged rom, needed signals for cpu not generated

          1. Ah! ok, you know what, I’ve not sent off that A4k mobo yet – i’ll give it a shot and see if i can get something out of it before i send it off. yeah i know it;’s been years, but “life” and stuff. 😀

  3. Good afternoon

    I want to ask for your help. I’m, I think, 99% finished assembling the Amiga 4000 motherboard replica ( And there’s a problem. It works on your DiagRom kit, passes all the tests, but after inserting the original kickstart 3.1.4 from Hyperion the board does not work. It shows a green and then a black screen. I don’t understand where the problem is.

    For ex.
    On DiagRom v1.2 – DRD(31:0) signals exist.

    Kickstart tests DRD(31:0) signals are missing.

    If you can help me, you can guide me on what to check why the DRD signal is missing, I’ll be very grateful.

    Best regards

    1. well it is hard to give a complete troubleshoot-guide.
      most common issue is that there is a bad solderjoint to alice.

  4. Thank you very much. I purchased a DiagROM for my A4000 and went into the memory edit function to edit $7F00000, and guess what, the memory controlled by U891 was stuck at 0xff. The symptoms were that 0 fastmem was detected.

    This was AFTER the board was cleaned in vinegar and IPA then repaired. It worked for a few months then the U891 intermittent then fail.

    I guess the chip must have continued rotting away unfortunately?

  5. Good day, i have a 4000 working but leaking issues. No clock, broken ram sockets, and leakage at the back where the audio filters are. But the Board is working fine.

    is it possible to send you the board and fix it on a new mainboard?

    Of course it cost money and time….
    please contact me on my email adress.

    keep on the good work.

    1. I can do that . in a couple of months. however it is quite a big job. so a move will be around 500eur

  6. Some days ago, my amiga 4000/030 with MMU strikes. 5-6 power blinks and then reset (loop forever). Grey color on crt-monitor (No boot picture), interrupted by blank screen(reset), if mouse is connected, else the screen starts distorted.

    Mouse & joystick directions havent work before but u could load workbench – now nothing.

    Keyboard reset seems to work and if u press both mousebuttons the power led stops blinking (probably u in startup screen – but nothing on screen).

    I guess the U975 joystick serial chip breaks the system down. Can i just remove the faulty chip and will i see the workbench or no chance with this approach. Any help would be nice.

    1. no U975 is important so you need to replace it. U976 can be removed. put a jumper from U975 from pin1 to ground and you can skip 976 totally

  7. Hi, I have an A4000 with A3640 that will not boot. After purchasing the Diagrom1.2.1 ROMs and installing them, I was able to enter the keyboard test but the key read of Diagram seems to always lag one keypress behind the next. Also after six (or so) key presses the program stopped registering (echoing) any keypress. Cntl-Amiga-Amiga gets me back to Diagrom but above behavior repeats. Further issue with CIA timer tests, Diagram doesn’t get past the test for the odd CIA. Also, port tests indicate port 0 “FORWARD” never registers, “LEFT” is always “ON”. Any suggestions as to whether these problems are related to the CIA U350, the A3640, or something else? Memory tests check out OK. Thank you in advance for any response!

  8. Hi Chucky

    You have more experiences like me, maybe you will know.
    I have one A4000 mobo, which had battery leaked and i repaired what i knew, (was only black screen) and now i have problem only with FastRam. No FastRam, I changed U981 and now i have dilemma. With yours DiagRom i see FastRam and i tested a whole range of FastRam, but with kickstart3.1 and Workbench 3.1 i see 0 FastRam. What can be bad yet ?
    Thanx in Advance

    1. close to the ram under the sockets there are 3 traces that goes to bottom side. one is _LED and one is IDE and also the memory RW maybe a problem there.

  9. Hi Chucky,

    I have a very weird issue that I just can’t seem to track down. A few years ago, I bought a basketcase A4000 with very bad battery damage and bad caps. I recapped the board, replaced the realtime clock circuit, replaced the f245 chip near the RTC, and replaced all simm slots. The issue is that some games and demos have sound that completely trainwrecks…the sounds run too fast, or the music tracks end up jumbled. This only effects a small subset of games and demos, and happens 4 out of 5 times when I start the machine. The 4000 occasionally boots up and runs those same games and demos with perfectly synchronized sound. The CIA chips all test as good in Amiga Test Kit, and the RTC seems to be working great. Any thoughts?

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