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I need help with a old 486 motherboard. I need the jumper manual

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First post, by renejr902

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Hi! google think it's a Chicony CH-486C. but it's not the same exactly. Check the picture.
i tried a 486 sx-25 and 486 dx-33 cpu and i tired with differents ram 30pins and different simm position. different video cards. the analyser card stay at 352F for 30 second and end at 643F. in manual for 64 = Jump to User Patch 1

on the board somewhere you can read: motherboard 486 - 25/33/50 DX/SX UCB Rev.A
i i tried without exterbe battery and with a extern battery. i found a jumper for this. the only one i know

Thanks for help.

I removed a battery that leak a little and cleaned. to my eye the lines the are good. i will check tomorrow the lines. for now i want the jumper manaul setting. Thanks a lot for help.

edit: my extern battery have 1.02v 🤣

Reply 1 of 7, by renejr902

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it seems to be this one:

DFI IB3486-UCB

edit: im not sure jumper dont seem the same

Nothing works. Thanks for help.

I need the jumper manual

edit: it seems to be this: DFI
486-25UCB/486-33UCB

https://theretroweb.com/motherboards/s/dfi-48 … 25ucb-486-33ucb

I have a different revision but it's the same motherboard.

I configured it with 32k cache and 486 DX-33 cpu compatible with crystal clock 33mhz. Same problem

643F

Reply 2 of 7, by majestyk

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Having the 3-chips RAM sticks in Bank0 might cause problems.
Remove all 4 of them and move the 4 sticks with 9 chips from bank1 to bank0.

Reply 3 of 7, by MikeSG

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For the pc analyser card codes w/ AMI BIOS:

35 - Reserved
2F - EGA/VGA not found. Display memory read/write test.

64 - n/a
3F - Reserved

Oxidisation of pins on reseatable chips and sockets (especially RAM, cache) can cause problems. Having L2 cache unpopulated may be a problem.

Reply 4 of 7, by rasz_pl

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those post codes do indeed look weird
try post card in another slot, press that button on post card and tell us what were the previous codes (it scrolls back)

https://github.com/raszpl/sigrok-disk FM/MFM/RLL decoder
https://github.com/raszpl/FIC-486-GAC-2-Cache-Module (AT&T Globalyst)
https://github.com/raszpl/386RC-16 ram board
https://github.com/raszpl/Zenith_ZBIOS Zenith Z-386 MFM-300 ZBIOS disassembly

Reply 5 of 7, by renejr902

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majestyk wrote on 2026-08-19, 11:35:

Having the 3-chips RAM sticks in Bank0 might cause problems.
Remove all 4 of them and move the 4 sticks with 9 chips from bank1 to bank0.

i already tried that. thanks

Reply 6 of 7, by renejr902

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MikeSG wrote on 2026-08-19, 11:57:
For the pc analyser card codes w/ AMI BIOS: […]
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For the pc analyser card codes w/ AMI BIOS:

35 - Reserved
2F - EGA/VGA not found. Display memory read/write test.

64 - n/a
3F - Reserved

Oxidisation of pins on reseatable chips and sockets (especially RAM, cache) can cause problems. Having L2 cache unpopulated may be a problem.

i cleaned everything correcty for 2 hours. it still does not work.

i just sold it 30$ to a guy and i just got another 486 vlb board that work 😀

But thanks a lot

Reply 7 of 7, by renejr902

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rasz_pl wrote on 2026-08-20, 00:37:

those post codes do indeed look weird
try post card in another slot, press that button on post card and tell us what were the previous codes (it scrolls back)

i sold it. But i didnt know the scrolls back thing. Thanks a lot

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