C151 looks like a bussed capacitor, located right behind the PS/2 ports.
I think it's next to the 'CN1' legend on the board.

Attached photo is of a 'straight' TUSL2, but the C151 bussed capacitor should be in the same place:

Eep386 got here first, but there's a copy of that link on the wayback: https://web.archive.org/web/20180218155846/ht … SLanguage=en-us

Sounds like they're talking about the capacitor network chip marked C151 (150nF maybe?) just behind the PS/2 port, I think part CN1 on the PCB silkscreen. If any of the 4 capacitors in that fails short then the keyboard would stop working. Not sure if it'd cause the other problems though.

Thanks, guys. Before I start forcibly ripping chips off the board, I am still looking for other suggestions. Not to discount the C151 as the cause of the problem, but I would prefer to save that as a drastic last option.

mrzmaster wrote on 2021-10-07, 15:50:

Thanks, guys. Before I start forcibly ripping chips off the board, I am still looking for other suggestions. Not to discount the C151 as the cause of the problem, but I would prefer to save that as a drastic last option.

Have you got a multimeter? If so, check the resistance between each pair of pins (from one side to the other) on that chip. They might not actually be open circuit, but they should all be some distance away from zero. If any measure near zero (say, under 10 ohms) then there's probably a problem there.

I see that motherboard has a jumper that changes the voltage supplied to the DRAM, chipset, AGP and PCI. It's 4 pins in a row, and has 3 positions. The middle position is listed as the default in the manual, is 3.40 V, and they strongly recommend you not change it.

What is yours set at? The jumpers look like they are next to the DIMM slots.

Do you have another motherboard you can test the RAM in?

snufkin wrote on 2021-10-07, 15:55:

Have you got a multimeter? If so, check the resistance between each pair of pins (from one side to the other) on that chip. They might not actually be open circuit, but they should all be some distance away from zero. If any measure near zero (say, under 10 ohms) then there's probably a problem there.

I do not but I can definitely look at picking one up.

Namrok wrote on 2021-10-07, 15:57:

I see that motherboard has a jumper that changes the voltage supplied to the DRAM, chipset, AGP and PCI. It's 4 pins in a row, and has 3 positions. The middle position is listed as the default in the manual, is 3.40 V, and they strongly recommend you not change it.

What is yours set at? The jumpers look like they are next to the DIMM slots.

Do you have another motherboard you can test the RAM in?

It is indeed at the middle position, 3.40V. I actually do have another spare board that I can try the DIMMs in and will give that a shot as well to try to rule them out as the cause. Thanks!

Update: I tested the RAM in another board and it's fine. I then removed the C151 chip per the other thread and it still doesn't post and beeps. I guess the board is dead. 🙁

It's unfortunate because this is the second problematic board in a row that I've dealt with (in one month) for this build. I just had to return a QDI Advance 10T to the seller because it arrived with the heatsink mount clips broken off of the CPU socket.

I'm scouting marketplaces for a suitable S370 board again. Patience is a virtue when it comes to retro builds, I suppose.

What's your SW1 set to? Could you post a photo of your board? If you get hold of a multimeter it might also be worth checking if the RAM slots have power going to them (measure voltage between the far ends, pin 1 and pin 84). There are a few large capacitors and FETs near the RAM slots that may be involved with supplying power for the RAM. Looks like the board was released in 2001, which was during the dodgy capacitor period, so check to see if any capacitors are bulging slightly, leaning at odd angle (caused by the rubber seals at the bottom blowing out) or have brown crusty stuff coming out the top.