Dead DayStar Genesis MP CPU card -- ideas?

[This Does Not Compute]

I have a DayStar Genesis MP with the quad CPU card, and it doesn't want to boot. Pressing the power button gets the system to power on, but there's no chime, video, or hard drive activity. The system has a brand new PRAM battery. Swapping the CPU card for another one, like a Sonnet G3 accelerator or dual-CPU card from a PM9500, gets the system to boot normally -- so the problem is clearly with the quad CPU card.

There's no info I can find about the card itself in terms of schematics. The heatsink puts a decent amount of pressure on the PCB, enough that the PCB flexes a bit, so my initial suspicion was that perhaps there were some loose solder joints between the CPU legs and the board. I reflowed all of them, but no change. Very briefly (less than 10 seconds) running the card without the heatsink let me find with an IR thermometer that the CPU at position U2 gets much warmer than the others. But I don't know if that's indicative of a short, or if that's normal since the classic Mac OS only uses one CPU unless application software is MP-aware.

The power pigtail for the CPU card reads the expected 3.3V. Barring a failed component on the CPU card (there are no electrolytic caps on it), does anyone have any experience with these machines?

 

[Kai Robinson]

Have you got any super hi res images of the card we can use to spot anything visually wrong?

 

[This Does Not Compute]

Have you got any super hi res images of the card we can use to spot anything visually wrong?

I'll see what I can do -- but I'm starting to suspect the motherboard. I dug out the dual-CPU card from my 9500 and while the machine boots with it installed, the DayStar utility reports that one of the CPUs isn't working. That *could* just be a software thing, but it's a bit peculiar nonetheless.

 

[This Does Not Compute]

So here's a super mahoosive photo of the card without the heatsink. The shiny parts around the CPU legs are flux residue, not solder bridges -- I inspected the card under the microscope for those.

I also recapped the motherboard just to get that out of the way, and there's no change. It still chimes and boots with the G3 card, so unless there's a *very* specific fault with the motherboard that only manifests with the quad CPU card, I don't think it's the problem.

 

[Elemenoh]

Pin 76 of U2 looks like it may be bridged to its neighbor.
The circled areas have some pins that look tarnished.

Have you already checked those areas closely?

 

[David Cook]

Is there corrosion on the inner contacts of J3? Or is that just a reflection? Is J3 connected to anything when the board is installed?

 

[This Does Not Compute]

Pin 76 of U2 looks like it may be bridged to its neighbor.
The circled areas have some pins that look tarnished.

Have you already checked those areas closely?

No shorts on any of the pins -- I examined them all under the microscope. Dark spots are just some flux residue, which I've cleaned up.

Is there corrosion on the inner contacts of J3? Or is that just a reflection? Is J3 connected to anything when the board is installed?

Looks like it might be a little tarnished, but nothing connects to it (or the pin header next to the card edge connector) from the system. I think it's probably only used for testing/debug during manufacturing.