I think I found the problem. I think any further triage should be put on hold until this one is solved. I spotted a missing surface mount capacitor. But I don't know its value to safely replace it.

My capacitance meter reads about 300uF on nearby ceramic capacitors. Could that be accurate?

If you look closely, it's actually visible in the first photo with the whole board.

no, your reading of 300uF is absolutely wrong.

Looking at the wider traces going to the capacitor it's very likely just a decoupling capacitor.

I only do repair as a hobby. I don't understand electrical circuits. Would a missing decoupling capacitor here cause the system to fail to post?

Probably not, it might just make the board a bit more unstable, or a bit noisier for EMC emissions.

For measuring capacitance, you can't measure a particular component when it's in a circuit. Each capacitor acts as a sort of reservoir/buffer/store between two points, that limits how quickly the voltage between those two points can change. When you try to measure the capacitance, you're measuring the size of that buffer between the two points. But if the two points are e.g. 3.3V and GND then there will be lots of capacitors between those two points, so you end up measuring the total capacitance, not just the one you put the probes on. When used for decoupling (smoothing the power supply close by to a particular chip), those little ceramic type capacitors are generally around 0.1 to 1 uF.

It works! After replacing the missing capacitor it came back to life!

I replaced the missing capacitor with a 1uF as this is all I had that would fit the footprint. I did have a 0.1uF but it was too small.

Thank you to everyone who offered advice on fixing this. The system is stable and the onboard Yamaha was even detected automatically by Unisound. I was able to get some sweet General Midi and OPL3 tunes out of this using the onboard Yamaha sound card. Sound Blaster FX also works great. It sounds amazing!

There is of course one NEW problem. The BIOS has a password lock on it. This doesn't prevent the system from booting but I can't get into the BIOS to change any settings.

Congratulations.

the password is a bummer though.
Looking at the board, and the jumperblocks near the flash... it looks familiar to some boards someone else here on the forum posted about with, I think, a password problem.
I think it was an intel board...
edit : seems like your board is an intel AN430TX

Another user found out that after clearing CMOS when BIOS asks you to press F1 or F2 like on your first picture you must go to setup. It won't ask for password first time . Disable security or change password immediately. What you're seeing is it's asking for password hardcoded in BIOS.

AlexZ wrote on 2021-08-12, 19:47:

Another user found out that after clearing CMOS when BIOS asks you to press F1 or F2 like on your first picture you must go to setup. It won't ask for password first time .

It definitely asks for a password even after clearing the BIOS.

Luckily there is a jumper option to disable the password. Worked like a charm. I've only heard about these jumpers in rumors and hushed whispers. This is the first time I've actually seen one in person.

Kahenraz wrote on 2021-08-12, 19:15:

It works! After replacing the missing capacitor it came back to life!

I replaced the missing capacitor with a 1uF as this is all I had that would fit the footprint. I did have a 0.1uF but it was too small.

Nice, so you found a board where one missing decoupling capacitor actually did make the difference, I really didn't think that it would make the difference between no beeps and it booting. Good work noticing it was missing.

The board looks to be very easy to maintain. There are only 5 small capacitors across the whole board and they are all the same 22u 25v value. They are surface mount but this makes it even easier to replace since it's just a solder blob on a large flat pad.

I'm very happy with it.

I wish the voltage regulator didn't get so hot but apparently this is within spec.

Actually, Intel even improved their VRM cooling design. Original was just flimsy aluminum sheet folded into something resembling proper radiator. This one has more mass and surface area.

It's impressive how much heat this thing puts out. I'm not used to having anything run this hot on a motherboard other than the CPU and GPU.

Kahenraz wrote on 2021-08-13, 21:05:

It's impressive how much heat this thing puts out. I'm not used to having anything run this hot on a motherboard other than the CPU and GPU.

Considering the AMD K6 233 has a typical power use of 17W, and it is run at 2.85V on your board, the vrm has to supply about 6A, which, with the thermal specs from the datasheet, will give you that high of a temperature 80°C, (roughly)

though since the amd cpu should be run at 3v3 (max 3v6) you could set it at 3v3, and thus the vrm would have to drop a little less voltage and thus would have to dissipate a little less power in heat.

but it's late, my math could be way off, I'mm of to bed and someone else will probably be so kind as to read what I said and either call my bs or acknowledge it.

Goodnight !

I was thinking about that. But then isn't it a trade off whether I want the VRM to work harder for create a lower voltage for a cooler CPU or run the VRM at 3.3v and let the CPU get a bit hotter.

Kahenraz wrote on 2021-08-13, 23:45:

I was thinking about that. But then isn't it a trade off whether I want the VRM to work harder for create a lower voltage for a cooler CPU or run the VRM at 3.3v and let the CPU get a bit hotter.

yes 😁

You can't change voltage on Intel OEM motherboard. It was designed only for Pentiums and automatically will detect if CPU have split rail voltage or not. Although you can force 3.3v vith CPU pin mod.

weedeewee wrote on 2021-08-13, 21:37:

Considering the AMD K6 233 has a typical power use of 17W, and it is run at 2.85V on your board, the vrm has to supply about 6A, […]
Show full quote

Kahenraz wrote on 2021-08-13, 21:05:

It's impressive how much heat this thing puts out. I'm not used to having anything run this hot on a motherboard other than the CPU and GPU.

Considering the AMD K6 233 has a typical power use of 17W, and it is run at 2.85V on your board, the vrm has to supply about 6A, which, with the thermal specs from the datasheet, will give you that high of a temperature 80°C, (roughly)

though since the amd cpu should be run at 3v3 (max 3v6) you could set it at 3v3, and thus the vrm would have to drop a little less voltage and thus would have to dissipate a little less power in heat.

but it's late, my math could be way off, I'mm of to bed and someone else will probably be so kind as to read what I said and either call my bs or acknowledge it.

Goodnight !

Sounds about right to me, although I don't think the gain is all that much as higher output voltage will also mean higher output current. I'm going to assume that current scales roughly linearly with voltage, and use 17W@3.2V Vcore typical from the cpu-world figures. 17W@3.2V gives 5.3A. At 2.85V the current drops to 4.7A (I think. I don't know if my assumption is any good), and the cpu power drops to 13.5W.

So with regulator output at 2.85V then it'll burn about 10.1W (4.7A, Vin 5V, Vout 2.85V), and at 3.2V it'll be about 9.5W (5.3A, Vin 5V, Vout 3.2V). For a heatsink that rises about 4C/W, then that's the difference between 38C or 41C above ambient.

I think.

Ya ready to bring this to life with a k6-3+? 😀

Re: Socket 5/7/SS7 (Voltage Interposer) Tweaker. (Released)

Yes, this is the one!

Kahenraz wrote on 2022-08-08, 06:59:

Yes, this is the one!

Order a 2+ 570? And mod it?

You’ll also want to check out this>
DIY Bios Modding guide Jan Steunebrink k6-2+/3+ 128gb