Mainboard problems

The only problem I’ve personally seen on a motherboard has been a blown voltage regulator.

The video one should be easy to track down, but assuming there’s no physical short, then it’s probably a bad VPU or video RAM. You could easily write a program to test the video RAM contents, but it could just be that the outputs to the display are shorted (also easily checked). But either way, component replacement is probably the only fix (IIRC, the VRM chip actually drives the display data lines, so if I was just gonna try swapping chips, that’d be my first guess).

I’m a bit surprised that the other would work long enough to boot, and then lock up. Does resetting make it get to the same spot again, or does it need a “cool off” period? I’d verify that the regulator is outputting a clean +5V, though I doubt that’s the problem (I ran a whole VB at 3.3V, and IIRC the only complaint was from the displays). You could also verify that the clock looks good, but it seems unlikely that the crystal would start up fine, and then fail. Again, you could write a simple test app… maybe you could determine that it only locks up when accessing a certain RAM area, or executing at a certain address. You could also probe the address lines and see where it’s trying to execute (whether it’s just off in the weeds, or maybe something is constantly interrupting). My first guess would be a bad NVC though.

DogP

Ah… yeah, if a cold boot gets farther than a warm boot, then a can of freeze spray (or even being very careful with a damp napkin and ice cube) could probably find the the problem component. But yeah, unless you’ve got a donor board, and the skills/tools to swap the components, it’s sorta moot.

Though really, if you’re able to solder VB displays, I’d guess that you could swap these chips. The nice thing is that the NVC and VRM are both on the top, so you wouldn’t even need to pull the motherboard from the system. Normally I’d use hot air for something like this… but with all the plastic in close proximity, I’d probably use Chip Quik. It’s just a matter of melting/globbing it on the chips, pulling them, using desoldering braid to remove the Chip Quik, and resoldering the chips.

I’d be glad to do it, but it’s probably not worth shipping all the way here to fix a couple systems… it’s probably more worthwhile to just keep them for spare parts.

DogP