Hey all, been a while since I posted, but wanted to share and discuss these two issues. I have a few VB’s for repairs here, where two mainboards are faulty, one just freezes up after the warning screen and sometimes after the VB IPD setting screen, the other just gives lines on both displays, switching out good displays or the mainboards with good working VB’s confirm that the problem lies with the mainboards (the board whit the cartridge slot).
The capacitors are still good and there is no visible damage to the boards, so I am assuming either the cpu or RAM is defective.

Anyone ever been succesful repairing these issues?

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

Thanks for your very informative reply, though (judging from your information) I am afraid the problems with these boards are beyond my skill set. I have measured the voltage regulators on both boards, just to be sure, and it came back completely normal. There are no apparent shorts in the display connectors, sockets or anywhere else.

With the one that freezes, it only gets through to the IPD setting screen at a cold boot, when it has been booted it stops at the warning screen.

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

If heat’s the problem, and cooling the chip in question solves it, maybe you could put small heat-sinks and/or fans in, and make it work with no part replacement.