VOGONS


First post, by Nexxen

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Hello lovely people,

I was gifted an unknown ISA Card from UMC, I'll go with the gpu model name, UMC UM85C405AF.
http://www.vgamuseum.info/index.php/news/item … -umc-um85c405af

I had some artifacting, decided to clean contacts. There were cracked solder joints on vram and size selector.
I removed all socketed chips and used some deox spray. After that no boot, no beeps either, detected but not working.

I found the problem, the chip UM9502 was mounted backwards. 🙁
Probably I mistook the dot for the indent of pin1. [head banging the wall]

Couldn't locate the datasheet but looking at other cards there are alternatives.
1. ICS2494N ----> probably my only choice
2. PALCE 16V8H-15PC/4 (but this is a programmable and good luck finding one + programmer + program diagram)

BIOS I can't read or write as I can't figure out what it is, UM23C256A-4227. Tried all same size with TL886 and always has a pin1 error.

Basically I'm looking for a substitute of the UM9502 and the an EEPROM to check if the bios is toast (guess not though).

Thanks for any input.

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PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 1 of 6, by mkarcher

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The BIOS is a 256 kBit mask ROM. You should be able to read it with any 27c256 setting - but you need to disable device ID verification.

The UM82c4010 on the picture in the VGA museum is obviously pin compatible to an ICS2494, which is a manufacturer programmable clock generator. But there are a lot of different editions of that chip with different programmed clocks. If you install an ICS2494 with a wrong set of clocks, some or all video modes will run at wrong refresh rates. The super VGA documentation collection "VGADOC" states about the ICS2494: "special versions such as the [...] UMC UM9502 exist", which might indicate that this chip uses a custom set of clocks that's not in any kind of standard ICS2494.

Reply 2 of 6, by Nexxen

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mkarcher wrote on 2022-11-29, 20:10:

The BIOS is a 256 kBit mask ROM. You should be able to read it with any 27c256 setting - but you need to disable device ID verification.

The UM82c4010 on the picture in the VGA museum is obviously pin compatible to an ICS2494, which is a manufacturer programmable clock generator. But there are a lot of different editions of that chip with different programmed clocks. If you install an ICS2494 with a wrong set of clocks, some or all video modes will run at wrong refresh rates. The super VGA documentation collection "VGADOC" states about the ICS2494: "special versions such as the [...] UMC UM9502 exist", which might indicate that this chip uses a custom set of clocks that's not in any kind of standard ICS2494.

I need an exact match to replace this 9502. That sucks.
Now I have to change the title with "Do you have a spare UM9502?"

Thanks for the explanation.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 3 of 6, by rasz_pl

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if that picture is of how it works at this point then your chip works, mounting backwards usually fries totally and there would be no output without proper clocks
if anything I would look for another ram

Reply 4 of 6, by Nexxen

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rasz_pl wrote on 2022-11-30, 03:47:

if that picture is of how it works at this point then your chip works, mounting backwards usually fries totally and there would be no output without proper clocks
if anything I would look for another ram

It is of how it worked before I made the mistake.

After it's no output at all.

Some ram chips had cracked solder joints, I guess it was probably that too.

After some research I found that this video card wasn't great, budget model.
I'm not crying about it.

Edit: I just put it back in to see if a miracle, but still dead. I see that the crystal has one lead with 3.04V, the other is 0.00V.
Maybe it says something to you.

Last edited by Nexxen on 2022-11-30, 17:33. Edited 1 time in total.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K

Reply 5 of 6, by mkarcher

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You can still try a ICS2494 from a different card. Many of those chips have the two standard VGA clocks (25 MHz and 28 MHz) as clock 0 and 1, so standard modes would work at the correct refresh rates, even if the clock chip is not as expected by the BIOS.

Reply 6 of 6, by Nexxen

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mkarcher wrote on 2022-11-30, 14:14:

You can still try a ICS2494 from a different card. Many of those chips have the two standard VGA clocks (25 MHz and 28 MHz) as clock 0 and 1, so standard modes would work at the correct refresh rates, even if the clock chip is not as expected by the BIOS.

If you know where I can find one 😀
I'll keep it there trying to locate one, maybe in time...

It's easy to help if you have the knowledge, thanks to you too.

PC#1 Pentium 233 MMX - 98SE
PC#2 PIII-1Ghz - 98SE/W2K