What was the wattage output of the original power supply? What are the voltage outputs? The P1 connector may supply the voltage for the floppy drive controller, so consider trying with a different floppy drive.

Is this a Deskpro/M series?

This computer does not use 3.3V wires.

Please post pictures of your homemade cable still plugged into the motherboard.

Cheers,

The power supply is a Compaq PS2021, part number 184735-001. Various places online say it is 145W, although I don't believe it is specified on the PSU itself. Voltage outputs are +5V, +3.4V, +12V, -5V, -12V.

I'm not sure if it is a Deskpro/M, I think it might be, it just says Deskpro 466 on it, no XE, XL nothing. The power supply does say +3.4v on it, and the pinout I was referencing also said 3.4v. Perhaps this was my mistake, assuming it would be fine to use the 3.3v wires from the ATX PSU. Another thing I really should have mentioned was that I have nothing in the -5V pin, since it seems that modern ATX PSUs don't have one. I did read that -5V is only used by the ISA bus and even then only by some cards, so I thought it would be alright. Maybe I'm a fool, and that is not true of this motherboard.

The pinout I referenced was as follows:

P1 connector (9 pins) : +12V, -12V, -5V, GND, GND, GND, +5V, +5V, +5v
P2 connector (8 pins): GND, GND, GND, +3.4V, +3.4V, +3.4V, GND

From http://matthieu.benoit.free.fr/Compaq_Prolinea575.htm

I did buy a multimeter and checked the voltages on all the pins, and I may have found a problem. All the 5V pins report 4.93V, all the 3.4V pins report 3.34V, but the +12V pin reports +12.4V and the -12V pin reports -11.3V. I know there can be some variance either due to the PSU or the multimeter's calibration, but those last two seem like they might vary a bit (maybe a lot) more than they should.

As for pictures of the cable it's quite a mess and you probably will have a hard time tracing which wire soldered to which, I did a bad job and they are all tangled up. This is what the connectors look like normally though
http://matthieu.benoit.free.fr/images/PS2021.jpg

My suggestion to you is to repair the power supply itself. These power supplies usually have two/three regulators, a bunch of caps and a protection circuit. And remember you have to connect something to the power supply before testing it with a multimeter.

Make sense this time. I was not sure.

The second set of plugs to the right is unknown. Only way is open up the power supply and see if you can get labelled voltages on these wires for each color.

Cheers,

I opened it up and didn't see any labelled voltages, unfortunately. I know it says ??? next to every GND on the second connector on that website, but I saw one person say they used this pinout and they reposted it exactly as it was on that website. They had a Prolinea, though, but the power supply and connectors are the exact same. I know, anecdotal but still. Also the original PSU was definitely a problem, one of the capacitors was leaking a lot. Glad it didn't start smoking or go up in flames while I was using it.

At this point I think I probably damaged the motherboard or something, since like I said it seemingly worked fine for a while then completely stopped working. While I initially thought that maybe by some chance the power supply I was using as a replacement failed too, this second one gets me to the exact same point. One of the LEDs on the front still light up, sometimes two will, but no speaker beeps. After some time of the PSU being on the CPU heatsink and various ICs on the board do get a bit warm though, so I really don't know.

At this point I'm considering just getting a new motherboard and trying to reuse the CPU and RAM in the current one. If I get one with a normal AT connector I should be able to just use an ATX to AT adapter and not have to deal withproprietary connectors anymore.

Only other thing I can think of is that I did a bad job of soldering and maybe I have some cold solder joints...

I have a Prolinea 5100e that I powered on with an ATX psu just to test. It posted but I didn't try anything further as the connections were really sketch and I didn't want to push my luck. I have 2 compaq psu's that are dead but I do have a Presario 9660 Tower I can test the pin out on as it works just fine.

Interesting, thanks for showing that. Unfortunately things aren't looking too good: Re: NEC PC-9821An: My crazy Japanese Socket 5 machine

and it's also known that if you use a CPU upgrade that grabs voltage from a floppy drive connector you can actually burn out the motherboard due to how the PSU regulates itself when it's not having 3.3v drawn from it.

Been looking at getting a PC98 and came across this post. Different system of course, but that bit about the floppy drive is concerning - mine has issues with the floppy drive being not being powered when the motherboard is plugged in - implying that it might indeed draw power from the floppy connector.. although at the same time probably not? since it's not like the floppy drive is plugged into the CPU.. just the floppy drive. Does anyone know anything about this? Sorry if this is something obvious that I should know