Distraction

On Labor Day my wife calls me to her studio to point out that her trusty Shuttle SD37P2 PC was making a strange noise. This was remarkable because this box has always been pretty quiet. Fitted with a “green” HDD and a fan-less PCIe GPU, the monitored fans would spin at a low speed, as there was not much power draw. I shut down XP and then popped the case to see the noise was coming from a bearing in one of the two rear fans. It was spinning, but making noise. When I rebooted, there was no BIOS, no video, and no blue LED on the front panel. Grrrr. This machine’s HDD and OS were well tweaked, and although I’m not worried about file-oriented data loss, a great many hours went into building up the OS state over two years. For example, I just installed and activated our copy of Adobe Photoshop on that machine, and I doubt it will be easy to recover that, for example. Never mind all the apps and software versions.

I hold my finger on the front panel power switch to start the PC, the PSU recognizes that, and I see the fans spin. I beep out +5 and +12 on the Molex pins, they are fine. But no video, and no BIOS. I look at the 3.3 tantalums bypassing the DDR DIMMs and there is nothing. Ok, that explains why no BIOS. This motherboard does allow tweaking the DRAM voltage, so that supply is off or dead. I find a bypass cap on the PCIe GPU adjacent to the 3.3 edge supply, and I see 3.5 volts. No 3.3 on the DRAM; hot 3.3 on the PCIe connector.

So I pop out the proprietary form-factor power supply, which Shuttle calls a model PC55, and I can see +5 and +12, but I don’t see any connector pin for +3.3. It doesn’t use the ATX standard. Oddly, the certification label calls out a few amps at 3.3; but provides no wires for that purpose. Suspicious. My guess is that the motherboard makes all the 3.3 it needs from +5 and +12.

I do the power-on/off dance a dozen times in a dozen variations. No evidence of any mechanical intermittent. I try to clear the CMOS by holding the clear-CMOS switch, on the hail-Mary that somehow the BIOS was corrupted on the last orderly shutdown. I have to set this aside now and get back to work. It seems unlikely that the motherboard 3.3 regulator(s) would just die. And it is a drag that I couldn’t find schematics and assembly drawings for the SD37P2 motherboard.