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286 PC - problems running with different VGA graphics cards

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First post, by jesolo

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Have a friend with a 286 PC that he's trying to get up and running.
Initially, there was a voltage line that was damaged which he repaired.

Upon trying to start up the PC, nothing happens (no POST error codes).
When he unplugs the VGA graphics card, he gets 8 beeps (video error).
After some trial and error with various graphics cards, he got it to boot with his Tseng ET4000 ISA graphics card but, with both his Trident & Oak VGA cards, the PC just hangs (nothing appears on screen and no beep error codes).

Any ideas or suggestions?

Reply 1 of 3, by Scali

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Perhaps the BIOS is not configured correctly?
In the BIOS you can select whether to boot up with CGA, MDA or EGA/VGA. If it is set to CGA or MDA, then the PC will not use the VGA card for its output.
Perhaps it 'magically' still works that way with a few VGA cards, but normally it won't (EGA/VGA cards have their own onboard BIOS extension, CGA/MDA/Hercules do not, and the motherboard BIOS handles everything in that case. That is not compatible with EGA/VGA cards of course).
So I would suggest putting in the ET4000 and checking that BIOS setting.

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Reply 2 of 3, by jesolo

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Thank you for the feedback.
The BIOS was configured correctly for EGA/VGA.

Another interesting development is that the Trident card has a jumper for 8-bit slot (in an AT) & 16-bit slot.
When he jumpered it for 8-bit slot and inserted it in the 8-bit slot, the PC booted. Doesn't work vice versa.

We suspect an error in the voltage supply to the 16-bit slot (he did try other slots as well).
Testing currently underway.

Reply 3 of 3, by Jo22

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It's a wild guess, but some ISA cards get their clock signal from the ISA bus, which in turn isn't correctly working on some PCs.
See http://www.os2museum.com/wp/the-isa-osc-mystery/

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In what to one race is no time at all, another race can rise and fall..." - The Minstrel

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