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.