Full Yes motherboard AT clock divisor problem \ VOGONS

Full Yes motherboard AT clock divisor problem

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First post, by theelf

Posted on 2025-12-13, 23:26

theelf Offline

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Posts: 1104
Joined: 2011-09-25, 19:39

Hi guys!

I have a Full Yes motherboard with Intel 82430FX. The problem is with the ISA bus clock.

https://theretroweb.com/motherboards/s/full-y … s-intel-82430fx

manual
https://theretroweb.com/motherboard/manual/82 … c1995080226.pdf

There is a jumper JP12 that controls the ISA clock divider:

2‑3 (default /4) → ISA 8 MHz

1‑2 (/3) → ISA 11 MHz

Even with the jumper in 2‑3, sometimes the ISA bus starts at 8MHz, and sometimes at 11 MHz. It is random, like a lottery. At 11 MHz, my PICOGUS card does not work.

I have checked:

The jumper contacts are clean.

The motherboard powers on normally.

BIOS settings (I/O recovery, PCI clock) do not change this behavior.

I want to know if anyone has seen this behavior and what they did to fix it.

Thank you for any help or advice!

Reply 1 of 3, by Matth79

Posted on 2025-12-14, 19:47

Matth79 Offline

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Joined: 2014-05-19, 14:24

Wonder if the jumper solder joints are bad, you could try reflowing, or soldering a bodge wire underneath across the 2-3 position

Reply 2 of 3, by theelf

Posted on 2025-12-15, 08:43

theelf Offline

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Rank: Oldbie
Posts: 1104
Joined: 2011-09-25, 19:39

Matth79 wrote on 2025-12-14, 19:47:

Wonder if the jumper solder joints are bad, you could try reflowing, or soldering a bodge wire underneath across the 2-3 position

Hi! thanks

No, jumper is fine, checked, i already tried to solder both pins

Caps near cristal checked and fine

Cristal 33mhz checked fine

I have no idea, the change 8.3-11mhz is random, some time start at 8.3 and stay for one week, some times 2 or 3 days always start at 11....

Reply 3 of 3, by Rwolf

Posted on 2025-12-15, 16:14

Rwolf Offline

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Location: Sweden

Sometimes it's the jumper connectors in the plastic house that is not gripping the pins properly; try a single pin on each 'hole'to see if it grips or is too open.
If so, and it is not easy to adjust , you can use unused jumpers from other positions on the board.

The tracks go to U24, which is the clock divider SC464, it could be worth checking the connections to that chip too.
https://datasheet4u.com/datasheets/Internatio … s/SC464/1561145

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