Need help debugging X68000 ACE HD

[js]

Hi!

A coworker got me an X68000 from Yahoo Auctions. Unfortunately, it only turned out later that the condition was marked "junk".

So I carefully turned it on. For a few seconds, it seemed fine (I didn't have a monitor attached), so I turned it off again. I noticed it smelled funny (hard to describe - I'd say a sour smell), so I turned it on again to see if it came out of the fan of the machine - and indeed it did. But on this second power on, after roughly 10 seconds, I got magic smoke. So I immediately turned it off and disassembled it, and sure thing, the PSU is dead. Also the battery has leaked.

I disassembled everything and cleaned up the leaked battery, checked the traces around the battery and couldn't find a dead one (I killed one trace while scrubbing it to see if it's still there, I already bridged it), but would not vouch for all traces still being 100% intact - I only couldn't find a dead one. I then attached an ATX power supply (and used an inverter for soft power), and it does turn on. I turned it on in a disassembled state, with just the mainboard, daughterboard and RGB module, and got no picture. After quite some fiddling (and even checking the 68000 CPU with an oscilloscope), I figured out that it seems that the CPU failed to talk with something on the bus, and got the idea to attach the riser card, and sure enough, I now got a picture. It's the common "System failure, please reboot" message, but it has a lot of noise in the background. When pressing reset, the noise goes away. When powering it off for only a short while and powering it on again, there is less noise (I attached pictures).

I already changed all caps (except a few on the RGB module that did not seem relevant - the entire RGB module doesn't seem all that relevant to the boot process), and the only thing that changed is that I now get a more stable picture that doesn't break up after 20 seconds (it stays for several minutes - haven't tried longer). I also tried pressing opt1 and opt2, as apparently that sometimes helps, but it made no change. I even did insert a floppy (albeit not one for an X68000, since I don't have any disks with software for it yet), but it did not even try to access it. I also noticed that when I am at this screen and press the NMI and reset button at the same time, the text fades out and I get a black screen. As in, with actual fade animation. Is this normal behavior?

Does anybody have ideas what I could try? Anything I should check? I'm out of ideas by now. I already looked at the serial port, and there's nothing. I guess I need some extra ROM for that in the unfitted ROM slots?

[leonk]

If you don’t do anything do you get to the insert disk screen?

[js]

No, only the screen above. I've never seen it output anything other than the pictures attached.

[leonk]

When you open the computer, on the floppy drive side and behind it is a small PcB for the external SCSI and floppy. Can you take a pic of the components on there and post here?

[kamiboy]

I've seen similar issues on various machines, and never could figure out what was wrong. I believe that generic error message comes up if anything goes wrong in the bootup chain, so the problem could be anything. It is a hardware problem though, and might be as simple as a broken trace, or as complex as a cutom IC having failed.

[js]

@leonk: I'm not sure what you mean exactly? The side with the floppy drives had no PCB - it only had space for the HD, the floppy drives and some connectors. Yes, the connectors are technically on a PCB, but there are zero components on it. Is that what you mean?

@kamiboy: Yeah, that's what I figured from browsing the forum already. However, there's two questions: Where is this noise on the video output on initial power off coming from and why does it go away when I press reset? That sounds like the initial initialization is going wrong, while the initialization triggered by the reset button works. And the other is: Is there any way to debug what it is?

[kamiboy]

The noise is prolly caused by VRAM being corrupted.

[leonk]

the bottom pcb of the computer has 2 ribbon cables coming up. they both connect to a circuit board located behind the floppy drives. I believe one of the cables is multi color. please post pics of that circuit board.

[leonk]

does it look like this or do you have missing components? like the blue resistor pack?

http://i.imgur.com/7NZqY81.jpg

[js]

@kamiboy: But then the garbage would stay after a reset, wouldn't it? And it would get new corruption over time? But after pressing reset just once, no noise comes back - the picture is clean post-reset.

@leonk: I don't have the board with me right now (I left it at my hacker space over night), but I'm quite confident that it had absolutely no components, which is why I didn't even bother attaching it for testing.

[js]

Here's the PCB without any components.

[js]

And here's the entire setup for testing.

[leonk]

Interesting.

So. this is the HD version. I wonder if this related to an issue I recently documented on the wiki. The SCSI is hanging because it’s not terminated.

https://gamesx.com/wiki/doku.php?id=x68000:black_screen_on_xvi_hd_and_potentially_other_hd_computers