Hello everyone,

I recently came across an Alaris Tornado 2 VIP board. Unfortunately, my photos of the board are too big to host natively, so here's an imgur link with a bunch of higher-res photos of what we're dealing with.

It's quite the interesting one, being made by the same Alaris that made the Leopard SLC2 boards and Cougar BL3 boards. It's pretty nicely-equipped, with an Efar Chipset (I think it's an SiS 471 clone, based on what I see on UltimateRetro) and OPTi 822 VLB-PCI bridge.

However, the dang thing just won't boot. I noticed, upon probing with a multimeter, that the voltage on the Vcc pins of the CPU socket was all over the place, wobbling between ~2.2-3.4V. Probing the ISA slots, I confirmed that the board is getting good 12V and 5V power from my ATX PSU. The ISA bus was operating at 6.3MHz, per my oscilloscope, and the 14.3MHz reference clock was good. My POST card showed no signs of life, and the board didn't want to boot no matter what I did. It came with a Cyrix DX2-v80, which is indeed good, but won't boot with any jumper configuration or tinkering.

I replaced the linear regulator MOSFET with an equivalent, known-good part and replaced the two electrolytics near the MOSFET, as they showed quite high ESR and were otherwise out of spec. The voltage issues improved somewhat, but the voltage is still somewhat inconsistent, hovering between 2.8-3.3V. The MOSFET is being fed a good 5V (really 4.9ish).

Unfortunately, I have no idea how the heck to set the jumpers on this thing and there's nothing on this board on UltimateRetro. The Alaris Leopard VX, a non-VIP variant of this board, exists there, but has a totally different layout in terms of jumper blocks. I can't figure out how to get the CPU voltage to change, so any help there would be greatly appreciated.

I noticed that a few of the SMD components near the VRM setup seemed...suspect, so I probed around some more with a multimeter and noticed that the LT1431 (seems to be an adjustable voltage shunt regulator) is getting a full 5V at its cathode pin; weirdly, it is not displaying the proper 2.5V on the reference pin. In reality, that reading fluctuated between 1.8 and 2.2V, staying mostly around 2.2V but bouncing around heavily. I suspect some bad SMD components may be at issue here and I'm not sure but I think that it's R22 in the VRM close-up photo that's at issue because the voltage is 5V on one side and the same ~1.8-2.2V on the other that the reference pin of the LT1431 showed. In fact, the two are in continuity, as per my multimeter.

So, does anyone have any thoughts on how I ought to proceed? Do I need to replace this one particular SMD resistor, or could there be something else going on here? Has anyone experienced anything similar?

I'd love to hear your all's thoughts. Thank you in advance for your input!