So I've been restoring a couple of WGS 9150s. One is an original (80mhz) and the other a 9150/120.
The 9150/80 was exhibiting these issues regularly:
crashing with type 1, type 2, and type 3 errors after some usage
internal video sometimes had random pixels of noise (in random colours) here and there
occasionally the internal video also didn't work, just a black screen on boot
I figured this was all probably RAM related. I removed all the SIMMs and the problems were still there. So then I suspected its 8mb of DRAM soldered to the board.
At this point I decided I might as well replace the 18 electrolytic caps on the logicboard and give it a good clean. The insides were rammed with dust and fluff! I think this machine had sat on someone's floor for years just sucking in all the dirt. It was quite a gross job.
Anyway it's all clean and has shiny new caps installed.
Now it doesn't seem to crash any more, but I get no internal video on boot, just a black screen. My monitor (an NEC 1880FX) knows there's something there as it comes off standby when I boot the machine, but it never gets a full signal.
(as a side note - video works fine from a Nubus card)
Anyone got any ideas? I suspect one or more of the DRAM chips has failed... or something else?
I've searched for schematics in vain. Not sure where to go next diagnosing this.
It’s probably a long shot but do you know if there’s any schematics out there for the LC 520 analog board? It’s a little hard to troubleshoot what’s going where without em.
I pulled the analog board out today and started testing capacitors with my ESR meter. Out of the 10 I’ve tested so far only one had an ESR reading that out of spec (and it was significantly out of spec, so maybe that’s part of the issue?). All the others were all in range. There’s 30+ capacitors on the board so I’ve still got a bit to go, but the bad one is definitely getting replaced.
I also double checked for cracked solder joints and I still don’t see any anywhere. Triple checked the flyback and surrounding areas and it’s all good. I’ll try hitting the pots with deoxit for good measure though.
I have a nice ratcheted RJ45/RJ15/RJ11 crimper as well. I got it at WeirdStuff surplus for cheap. I used it a lot when I worked at a different school campus, but my new work insists on buying molded ethernet cables. I understand the paranoia, but, I did like crimping my own cables and using them. Was pretty satisfying.
If I ever get my own house, I'll make PLENTY use of it wiring up ethernet and phonenet.
Was able to rule out the monitor using a very hacky hack to get some signal directly to a separate VGA. I didn't know how to deal with the grayscale, so I just sent it to green -- and you can see the same pattern shown. So its something on the logic board. I guess I'll proceed with ordering some caps, and see if that fixes anything (but I doubt it)