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K6-2 350 having issues with 100 MHz FSB

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First post, by Painy

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I recently bought a cheap LuckyStar 5MVP3 rev 3 with a AMD K6-2 350.
Win98SE installs and runs when FSB is set to 95MHz or lower (tested 4*95 = 380MHz and 3.5*95 = 333Mhz).

If I set FSB to 100MHz and multi to 3.5, it shows up as 350MHz in BIOS but windows immediately shows a bluescreen on startup. Also when I try to run Win98SE setup from CD it gives me a SUWIN error. Same thing happens if I set the multi to something lower.
Switching back to 95MHz FSB and it's booting/installing fine again.

A capacitor near the AGP port shows some brown/red stuff on top, could this be the issue?
Other caps on the board look good.

I updated the BIOS to LEB7-03.4 already with no improvement (it came with version AU6-03).

Other hardware installed: 64MB PC100 SD RAM (tested with other working RAM PC66/100/133 of various size, same issue).
Voodoo 3 2000 AGP which works fine in my other vintage systems.
Quantum Fireball 13.6GB in UDMA33 mode using 80-pin wire (also tested with other working HDD and cable, tested in PIO mode too).
Non-branded AT power supply with unknown power output. Voltages are fine when tested with a multi, caps inside also look good too.

Via 4in1 v1435 drivers didn't help either.

Could this issue come from the capacitor with brown stuff near AGP port? Or maybe is the power supply broken or too weak? Any other ideas?

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Reply 1 of 5, by dionb

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Painy wrote on 2023-02-10, 15:18:

[...]

A capacitor near the AGP port shows some brown/red stuff on top, could this be the issue?

Yes. Very much. Those caps help regulate and smooth the voltage being delivered to components on the board. If they're shot, the components are getting unstable or incorrect voltages, which at best can lead to instability and at worst catastrophic failure (i.e. the magic smoke coming out).

Also, caps start failing long before any damage is visible on the outside. If one cap of a particular type is leaking, all caps of the same type should definitely be replaced, and to be safe, consider replacing every single electrolytic cap on the board.

Reply 2 of 5, by Sphere478

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Few things that I have seen cause stability at low freq and instability at stock freq

Voltage too low,

Bios not updated for cpu being used, (check for a Jan Steunebrink bios) Re: Diy modding support for k6+And 120gb hard drives into bios roms

Bad caps.

Sphere's PCB projects.
-
Sphere’s socket 5/7 cpu collection.
-
SUCCESSFUL K6-2+ to K6-3+ Full Cache Enable Mod
-
Tyan S1564S to S1564D single to dual processor conversion (also s1563 and s1562)

Reply 3 of 5, by dionb

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If the BIOS didn't support the CPU at 100MHz FSB, it also wouldn't at 95MHz. Voltage setting wouldn't be an issue as the pic shows lowest configurable voltage is 2.1V. A K6-2 requires 2.2V, and 2.1V is within 5% margin of that. So insufficient voltage means something in the regulation is going wrong - and we're back to the - visibly - bad caps again...

If we know there's a hardware defect that could cause exactly the symptoms displayed, that's always the first thing to resolve. No point in trying to work around it with settings.

Reply 4 of 5, by Sphere478

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dionb wrote on 2023-02-10, 16:44:

If the BIOS didn't support the CPU at 100MHz FSB, it also wouldn't at 95MHz. Voltage setting wouldn't be an issue as the pic shows lowest configurable voltage is 2.1V. A K6-2 requires 2.2V, and 2.1V is within 5% margin of that. So insufficient voltage means something in the regulation is going wrong - and we're back to the - visibly - bad caps again...

If we know there's a hardware defect that could cause exactly the symptoms displayed, that's always the first thing to resolve. No point in trying to work around it with settings.

cpu speed thing vs bios:
That’s what I thought once also 😀 until I had a few mobos that wouldn’t boot at speeds higher than (somewhere around 350mhz actually) with my k6-3+ chips until I updated the bios.

You mistake me, I agree it is most likely the caps I was just listing all things that came to mind.

Sphere's PCB projects.
-
Sphere’s socket 5/7 cpu collection.
-
SUCCESSFUL K6-2+ to K6-3+ Full Cache Enable Mod
-
Tyan S1564S to S1564D single to dual processor conversion (also s1563 and s1562)

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