Could replacement capacitors be related to stability issues on my motherboard? \ VOGONS

Could replacement capacitors be related to stability issues on my motherboard?

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First post, by Kahenraz

Posted on 2022-02-22, 01:53

Kahenraz Offline

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I replaced all of the capacitors on a vintage Slot 1 montherboard with genuine Nichicon capacitors which I ordered from Digi-Key. While the system appears to work, I have since found that it is unstable when doing an ACPI shutdown or reboot from Windows 98/ME.

The symptoms are that the system will shutdown and turn itself off when "shutdown" is chosen but "reboot" will hang on a black screen with a blinking cursor, requiring a manual reset. Both options result in the system starting up with Scandisk after detecting an incorrect shutdown (even though it appears to shutdown correctly when this option is chosen).

The strangest behavior is that if I use the power button instead of the reset button when the system is hung on the blinking cursor, it will NOT turn back on and appear "dead", even if the PSU is toggled on and off and the power cable is reseated. To revive the board, I have to have the PSU off and hold the power button to drain the capacitors. Only then will the system turn on.

I chose these capacitors specifically because of their brand name and low impedance but I wonder if the fact that the HV(M) series capacitors, which the datasheet says has a +/- 20% tolerance has created this issue.

I don't know if the motherboard had this problem before the recap as I hadn't performed this exact test. It's an uncommon model and I've never been able to find an exact replacement to confirm how it previously performed stock. I have many vintage motherboards, but this is the only one that I've done a full recap of all of the large 470uF capacitors.

The motherboard is a Shuttle HOT 675V with a VIA VT82C691 Apollo Pro chipset. I am using the latest BIOS version 675VS026 available from Shuttle.

Does anyone have any thoughts on this?

Last edited by Kahenraz on 2022-02-22, 05:30. Edited 3 times in total.

Reply 1 of 8, by stamasd

Posted on 2022-02-22, 02:05

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If in doubt, it's never a bad idea to replace with higher capacity caps. The extra capacity helps with the filtering, and the ESR decreases with capacity increase (higher capacity in the same series = lower ESR).

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Reply 2 of 8, by TheMobRules

Posted on 2022-02-22, 02:13

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Most of those electrolytics are 20% tolerance, so that should be OK. HV series is probably better than the best electrolytics that were available during the Slot1 days.

That error seems a bit too specific to be related to the caps, have you tried any software that can stress the system? If the new caps aren't doing their job properly it would probably manifest as all kinds of instabilities.

Also, do you still have the original caps that you replaced? What brand/series were those?

Reply 3 of 8, by Kahenraz

Posted on 2022-02-22, 02:25

Kahenraz Offline

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I did this recap years ago and don't have the originals anymore.

I took a closer look and found that all of the capacitors I replaced along the CPU are 1000uF 6.3V VZ(M) series. The datasheet says that they are designed for a wide temperature range and do not mention low impedance. Could this be related?

I double-checked that all of the capacitors are oriented with the correct polarity. I'm not sure what else to test for. I've never seen problem manifest before on other motherboards.

Reply 4 of 8, by TheMobRules

Posted on 2022-02-22, 03:00

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VZ is a general purpose series, so definitely not low impedance. If the originals were low ESR (very likely if we're talking about the caps around the CPU) then these will struggle.

Reply 5 of 8, by maxtherabbit

Posted on 2022-02-22, 03:54

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Replacing the CPU bypass caps with low ESR seems like a good idea, but I seriously doubt that's the cause of your specific problem

Reply 6 of 8, by Kahenraz

Posted on 2022-02-22, 05:19

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I just finished replacing all of the VZ capacitors with low impedance caps but there was no improvement.

This board is very odd.

Reply 7 of 8, by Kahenraz

Posted on 2022-02-22, 05:29

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I went into the BIOS and under "Power Management" set "ACPI function" to "Disabled".

This seems to have fixed the reboot hang and shutdown problem. The system still powers itself off when "Shutdown" is selected, which is a function of ACPI, so I'm bit sure what this feature actually does.