Need Help with my Amiga 4000

[slammers]

I have a 4000 (non-tower) that has been sitting around for years and decided to try and fire it up. Unfortunately it just gave me a blank screen. I checked the battery and it had a minor leak so I removed it and inspected the PCB and could not see any signs of damage.

I unplugged the HDs and Floppy powered it up a few times. On one occasion it actually booted and gave me the screen saying 3.0 Roms and the animation to insert the Workbench disk.

So I plugged in the floppy and tried again. It took quite a few power cycles but managed to get the boot screen again and load up Workbench 3.0 off floppy. It showed I had my full 2mb chip ram and 8mb fast ram. I browsed the disk and everything seemed to work. It worked for maybe 15 minutes and then the pointer froze. The screen remained active.

So I then plugged in my HDs to see if I would get lucky but unfortunately I have not been able to get it to work since, even unplugging all the peripherals.

The keyboard seems to work, the caps light blinks when I power up. If I press Ctrl-A-A the light blinks and the HDs cycles.

The motherboard looks very clean. There is no sign of bulging or leaking caps. I used meter to check all the electrolytics and none had shorts. I guess they could still be bad but there was nothing obvious

The power supply seems ok, I get 5.08V, 12.02 and -11.96. According to my scope they are all nice an clean. No ripples of any kind.

I could not detect any noticeable hot spots. The Alice chip gets a little warm (36C) but not extreme.

So I am looking for some advice on how to proceed. I am a little confused on the color sequence, when mine did work it only went from black to dark gray before the bootup menu appeared. Does the 4000 go through all the startup colors?

Since the screen stays black is that a sign of the processor not detected? Is there a signal I can probe that would indicate whether the processor is detected?

I put my scope on some of the Zorro slot pins and see activity. C1 and C3 are 3.57Mhz.

I also have an Amiga 3000 that does work. Is it possible to plug the A3640 expansion card into the 3000 to see if that board is the problem?

Thanks for any help you can provide.
Shawn

[slammers]

I did that when I removed the battery from the mother board. Also re-seated all socketed ICs including the ROMs, the 68040

I have removed and reseated the A3640 multiple times.

[slammers]

I did some more research and I have the rev 3.0 A3640 board with the issues with C105 to C107 being backwards. I checked these caps and they were not leaking but I changed them out and corrected the polarity.

I did notice the C102B and C102E were leaking. So I replaced those as well.

Unfortunately it still would not boot.

So I looked at the 200 pin Local Slot connector under a microscope and I could see some form of contamination of the gold plated contacts. It looked very odd. So I cleaned that up with some contact cleaner and that seemed to fix the issue. Now have a working 4000.

I am not sure if the video is working completely though. I can use my Commodore 1080 to get to workbench but when I run some apps the screen goes black. If I do some mouse button magic I can get back to the workbench. If I drag the workbench window down, there is a window behind it that is grey and has random black pixels everywhere.

It may just be that the video is running at a higher rate than my monitor can handle. I have an NEC Multisync 3D that I am sure I used on the 4000 but I seem to have lost my Commodore DB23 to DB15 adapter. I have EGA to VGA adapter but that does not seems to work (DB23 to DB9 cable -> DB9 to DB15 adaper, -> NEC VGA cable from monitor). I suspect the pin outs with this combination are just wrong.

Is there a connection diagram for DB23 to VGA available so I can make something up?

[slammers]

Thanks a lot. I found another a something myself but did not indicate the buffers for the sync lines.

I will make one of these up once my DB23s arrive.