mkarcher wrote on 2023-10-16, 20:30:

Chadti99 wrote on 2023-10-16, 20:10:

mkarcher wrote on 2023-10-16, 19:36:

And indeed, the RGB524 is a 5V tolerant 3.3V chip.

That is interesting, I wonder why the VRM is needed. I can def put a meter on it.

If you still wonder why there is a VRM, I am sorry for using expert-only terms which were not clear enough. "a 5V tolerant 3.3V chip" means that this chip is a operating with 3.3V supply voltage. That's why the VRM (actually, it's not a voltage regulation module, just a voltage regulation chip) is needed. The IBM RGB524 will possibly blow up if you feed it with 5V. So why did call it 5V tolerant then, if it can not tolerate 5V supply? Because in electronics design language, this term is defined to mean "this chip can handle 5V on the data/signal lines even if it is powered by a lower voltage". The standard way of constructing chips designs input in a way that they are moderately resistant against ESD (electro-static discharge), but they can't withstand voltages above the supply voltage or below GND, because that case is treated like ESD. While small electro-static discharges have high voltage, they only have a tiny amount of power, so if the chip shorts that power out, the danger is gone. On the other hand, if you actively and continously supply voltages outside the permitted range, you might damage the chip.

"5V tolerant" means the chip is built in a special way that the ESD protection circuit is modified in a way that 5V on the data pins is not shorted to the 3.3V supply pin, so the chip works without any trouble when it receives 5V signals on some or all of its inputs (in case of the IBM DAC, all the signals it receives are 5V signals).

Got it, makes sense, appreciate that detailed explanation. Probably makes sense to check the voltage coming out of that VRM?

Chadti99 wrote on 2023-10-16, 20:34:

Got it, makes sense, appreciate that detailed explanation. Probably makes sense to check the voltage coming out of that VRM?

If you can easily check it without shorting anything while trying to do so (best case: the mainboard is not mounted in a case, and there are no other cards near to it), testing the VRM makes sense, because it's easy. I don't think a broken 3.3V regulator is likely, though. In what way does the card "show no signs of life"? Does the computer still boot with the card installed? Does it emit the typical "no graphics card installed" POST error beep?

mkarcher wrote on 2023-10-16, 20:43:

Chadti99 wrote on 2023-10-16, 20:34:

Got it, makes sense, appreciate that detailed explanation. Probably makes sense to check the voltage coming out of that VRM?

Does it emit the typical "no graphics card installed" POST error beep?

Exactly this, one long beep then three short. Quick pause between first two short beeps. No output to monitor.

Chadti99 - would you be able to dump the bios from the S3 Diamond SE VLB card and post it here or upload it to the vgamuseum? I have a card that's missing the bios. I think we can probably just use the same bios as the PCI cards use, but would be curious to compare 😀

Is that the S3 Trio32? Not sure I still have it, let me know. I could source another though.

What did you end up doing with that VLB S3 968 card? From my experience when testing various PCI 968 cards, the cards with the TI RAMDAC output a much clearer output image compared to the IBM RAMDAC. I focused my comparison on the 1280x1024 resolution.

I still have it, will probably build a system around it soon.