Do the motherboards still boot with the card installed? E.g. POST beep and POST codes associated with booting? A POST card would be handy so you can watch the codes on the bus and compare between a working card and non-working card. It may not help with fixing it, but would let you know if it's totally dead and stalling the boot process versus semi-working but just not outputting any video.

I don't have any specific advice, I don't have any experience repairing TNT cards. But my first thoughts would either be a possibly bad capacitor on the board, or perhaps the VRAM is no longer working correctly (a more difficult part to replace).

PC starts , HD (led blinking) and cd rom initiate as well as cpu fan spins. Howevere there are no post beeps of any kind and it looks like the system hangs before beeps hapen. The behaviour is same even if i select integrated gpu to be the first video output or if i instal other pci gpu and hookit to monitor if tnt is also present in the system. This behaviour is the same on any other motherboard i tried the tnt.
I checked the card for any visual problems bu there are no bulging capacitors, pci contacts have been cleaned and all soldierpoints ( resistors, capacitors and memory pads ...)have good contacts.
Saddly i dont have post card to check for "life sighns".

Blitz_25 wrote on 2023-10-23, 21:53:

PC starts , HD (led blinking) and cd rom initiate as well as cpu fan spins. Howevere there are no post beeps of any kind and it looks like the system hangs before beeps hapen. The behaviour is same even if i select integrated gpu to be the first video output or if i instal other pci gpu and hookit to monitor if tnt is also present in the system. This behaviour is the same on any other motherboard i tried the tnt.
I checked the card for any visual problems bu there are no bulging capacitors, pci contacts have been cleaned and all soldierpoints ( resistors, capacitors and memory pads ...)have good contacts.
Saddly i dont have post card to check for "life sighns".

If you're interested in retro computing definitely pick up a POST card. I'm clocking them at about $10 USD shipped on eBay. They won't fix your problem, but they will help show what is going on within the board. One can lookup the code + BIOS mfg to get an idea of what is going on. You may still need to work on the TNT, either via capacitor replace or VRAM replace, or to replace the whole board which is a bummer but sometimes needed.

Might be cracked solder joints. Surface mounted chips might also have a connection that is just touching but no longer actually soldered, if you try to gently wiggle or move them, you'll be able to see if they're all still connected.

Ok, will invest in diagnostic post card, do you have any recommendations from what seller on ebay i should get as there are heaps of them there to be get and i guess not all POST cards are alike.

I field a claim on ebay for return (em 2days over return window) so will wait if seller will accept the claim.
If i'm stuck with the card i'll check the soldier contact in detail as well as caps and resistor check with multimeter. if needed i'll do a reflow of solder pads with a heat gun

I don't think that POST card will be better than std BIOS beep codes. Is a speaker connected to your motherboard?
One long three short means no card detected so it's either GPU or card power line.

Problem is that system hangs before post beeps even happen so i dont get any "info" from the motherboard hence why post card would be usefull

What intriges me is what sort of mailfunction of vga in PCI slot prohibits boot even if one has set in BIOS as primary video output an Oboard vga or AGP vga and also hook monitor on either of this two as PCI vga in such configuration is not intialized as video output device at this early stage?
I would presume that in such condition one would simply not be able to instal device and drivers in OS as it would not be recognized correctly if at all. I had similar problems with failing vga and system would boot up properlly with other vga card as primary and in OS the failing vga on PCI installed as secondary would simply not show up or if shown in control pamel there would be some sort of error message when trying to instal drivers.

Could there be some kind of short happenig on PCI slot through vga card preventing to even start booting🤔 in the first place?

Blitz_25 wrote on 2023-10-24, 16:56:

Could there be some kind of short happenig on PCI slot through vga card preventing to even start booting🤔 in the first place?

I'd say that's exactly the problem, if bios doesn't even get to init subsystems

Blitz_25 wrote on 2023-10-23, 19:29:

Any advice on how to procede with identifieing the problem of the tnt card and possible fixing solutions?

Is your Vanta's BIOS chip OTP EPROM? I've similar problem with TNT2 M64 Pro and I can't find proper BIOS even after I swapped the OTP EPROM with compatible EEPROM: Re: I need help to repair an old NV RIVA TNT2 Pro/32M card

Can't tell you what sort of BIOS chip it had as i sent the card back for refund. On the chip it self there was no sticker/label or markings what so ever also no uv "erase window".

Blitz_25 wrote on 2023-10-27, 19:03:

Can't tell you what sort of BIOS chip it had as i sent the card back for refund. On the chip it self there was no sticker/label or markings what so ever also no uv "erase window".

OTP (E)PROM isn't EPROM with UV-light erase "window", it's One Time Programmable (O-T-P) ROM-chip. And every non-voltiare memory degrades over years.