Excellent troubleshooting info! Thanks.
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)
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
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.
THIS IS NOT A COMPLETE “GUIDE” AND WILL BE UPDATED ETC.
20 thoughts on “Amiga 4000 Hardware”
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?
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)
I want to ask for your help. I’m, I think, 99% finished assembling the Amiga 4000 motherboard replica (https://acillclassics.wordpress.com/a4000-replica-project/). 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.
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.
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?
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.
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.
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!
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