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Soltek SL-75KAV Socket A motherboard not powering on

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First post, by mwiik

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I inherited a faulty Socket A system recently. It didn't power on at all, no activity when pressing the power button or otherwise shorting the power pins. When shorting the PS_ON pin directly on the ATX connector on the backside of the board, the fans spun up, but they stopped as soon as I removed the screwdriver. Keeping the pins shorted kept the fans running, but it didn't post (obviously).

There were quite a few bulging caps, so I did a partial recap and replaced them. I replaced all the large caps around the CPU and ATX connector, and a few smaller ones elsewhere. After that, the board powered on and POSTed! Success! Or so I thought. I played around with it for an hour or so with several reboots. Then it just suddenly stopped working again in the exact same manner after a power cut. One thing I did during the power cut was to install a PCI NIC, although I have a feeling that wasn't the cause. The previous owner said that it powered on twice before suddenly dying.

So I replaced the rest of the 1000uF caps, which means I have replaced all 1000uF and up. No luck. Still completely dead. I have tried three different PSUs, all of which work fine on another machine.

This is my first attempt at reviving an old board, so I'm not really sure how to proceed from here. Any tips on what to check next would be very much appreciated. I'm guessing there's something going on with the power circuitry, but I'm not very familiar with the inner workings of the power on sequence. There is 3.5V across the power pins and 5V on the WOL header, so at least there's some standby voltage.

I'm hoping I can introduce my son to some retro gaming during the winter. 😀

Thanks in advance!

Reply 2 of 11, by ciornyi

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giantclam wrote on 2023-10-12, 23:41:

Try replacing the few tantalum caps onboard

There is no such caps presented at this board.

To OP I'd try reflash bios if it possible

DOS: 166mmx/16mb/Y719/S3virge
DOS/95: PII333/128mb/AWE64/TNT2M64
Win98: P3_900/256mb/SB live/3dfx V3
Win Me: Athlon 1700+/512mb/Audigy2/Geforce 3Ti200
Win XP: E8600/4096mb/SB X-fi/HD6850

Reply 3 of 11, by giantclam

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ciornyi wrote on 2023-10-13, 05:34:
giantclam wrote on 2023-10-12, 23:41:

Try replacing the few tantalum caps onboard

There is no such caps presented at this board.

You saying it differs from this example?

nTR6tsJ.png

Reply 4 of 11, by Doornkaat

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giantclam wrote on 2023-10-13, 05:49:
You saying it differs from this example? […]
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ciornyi wrote on 2023-10-13, 05:34:
giantclam wrote on 2023-10-12, 23:41:

Try replacing the few tantalum caps onboard

There is no such caps presented at this board.

You saying it differs from this example?

nTR6tsJ.png

Instead of ticking all boxes you boxed all ticks.😉

Reply 5 of 11, by mwiik

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giantclam wrote on 2023-10-12, 23:41:

Try replacing the few tantalum caps onboard

Thanks. I can see three tantalum caps if I'm not mistaken, one of which is connected directly to the power pins. If I'm reading the markings right, it's a 10uF 16V capacitor. Please correct me if I'm wrong so I don't order the wrong parts. 😉
Is there a way to test tantalum caps in circuit?

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Reply 6 of 11, by giantclam

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Doornkaat wrote on 2023-10-13, 05:53:

Instead of ticking all boxes you boxed all ticks.😉

Lol ... that's one way of putting it ... =)

mwiik wrote on 2023-10-13, 06:06:
giantclam wrote on 2023-10-12, 23:41:

Try replacing the few tantalum caps onboard

Thanks. I can see three tantalum caps if I'm not mistaken, one of which is connected directly to the power pins. If I'm reading the markings right, it's a 10uF 16V capacitor. Please correct me if I'm wrong so I don't order the wrong parts. 😉
Is there a way to test tantalum caps in circuit?

Yes and no...they have so called 'self healing' properties and may test OK but be bad in circuit ; as they're only cheap, I just replace them as matter of course. Yes... 10uF @ 16VDC ...

Reply 7 of 11, by ciornyi

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giantclam wrote on 2023-10-13, 05:49:
You saying it differs from this example? […]
Show full quote
ciornyi wrote on 2023-10-13, 05:34:
giantclam wrote on 2023-10-12, 23:41:

Try replacing the few tantalum caps onboard

There is no such caps presented at this board.

You saying it differs from this example?

nTR6tsJ.png

Sorry my bad

DOS: 166mmx/16mb/Y719/S3virge
DOS/95: PII333/128mb/AWE64/TNT2M64
Win98: P3_900/256mb/SB live/3dfx V3
Win Me: Athlon 1700+/512mb/Audigy2/Geforce 3Ti200
Win XP: E8600/4096mb/SB X-fi/HD6850

Reply 8 of 11, by timsdf

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List what I'd try after tantalums:
-Replace caps around chipset and ram (specially the green ones)
-Are you sure dip switches are in correct positions? Test if 100FSB setting boots
-Test another cpu, ceramic athlon/duron cpu can get damaged/cracked pretty easily on the die
-If board tries to boot but shuts down: contact cleaner spray on ram slots / AGP and test a few other sdram / gpus

Reply 9 of 11, by Karbist

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There's a small 5v to 3.3v regulator between PCI 3 and 4 slots, disconnect the power connector and measure the resistance between where I have pointed the arrow and the ground, on a healthy south bridge chip it should measure more than 150 ohms.

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connect the power and measure the cmos clear jumper to the ground, you should have more than 3v on this jumper.

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since the south bridge chipset also has integrated super I/O, put the motherboard on a flat surface and apply pressure with your finger on the south bridge chipset, then try to power on the board.

Reply 10 of 11, by mwiik

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Karbist wrote on 2023-10-13, 16:59:

There's a small 5v to 3.3v regulator between PCI 3 and 4 slots, disconnect the power connector and measure the resistance between where I have pointed the arrow and the ground, on a healthy south bridge chip it should measure more than 150 ohms.

It measures around 145 ohms. A bit low?

connect the power and measure the cmos clear jumper to the ground, you should have more than 3v on this jumper.

3.1V is indeed present at the jumper.

since the south bridge chipset also has integrated super I/O, put the motherboard on a flat surface and apply pressure with your finger on the south bridge chipset, then try to power on the board.

No change unfortunately.

Thanks for taking the time!

Reply 11 of 11, by mwiik

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So I received the new tantalum caps the other day and replaced them. At first there was no change, but then it suddenly jumped to life and has been working perfectly since. Kind of odd, but I'm happy as long as it's running.

I installed Windows 98 and started playing around with it for a bit. It has never failed to power up since, but the system feels a bit unstable. It hangs or is extremely slow for a bit sometimes, and half the times I have to reboot to fix it. Maybe I should go with XP instead, unless it's a hardware issue.

Anyways, thanks for all the help in this thread. I really appreciate it.

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