Video card MOSFETs crushed... need to replace them?

[gonzo0815]

Re: Video card MOSFETs crushed... need to replace them?

Oh well, have a GF6800 ultra (or something like this, it was the best possible card from that chip) laying around, wich had suffered a broken vt chip too. I have hard times in googling abouth it, in the end there are some chinese partdistributors who sell this thing. But i never found any datasheet or similar on them. I thought on to replace it with an usuall mosfet, i asume it ins`t that easy withouth datasheet (any short will fore shure kill the card and may be the motherboard too), but from my point of view, this are nothing else than ordinair mosfets, directly chipcased and soldered with a BGA style soldermask. The controler chip is on those boards usually soldered at the bottom side of the card. Up to now i havent had the guts to do it.

[linuxguru]

Re: Video card MOSFETs crushed... need to replace them?

Hmm - the VRM chips appear to have the power switching devices integrated in them. The card seems to have a 5-phase section, and two-separate 1-phase VRMs with different controllers. Why they chose to package it in a BGA beats me - an 8-pin DIP or 3-pin package like the TOPswitch would be far easier to rework. The BGA looks certain to let the smoke out on an overload or short - I doubt that it can dissipate more than 100 mW. How much current can a BGA solder-ball or PCB trace to a BGA pad carry anyway?

[PR373ND3R]

Re: Video card MOSFETs crushed... need to replace them?

I'm, trying to get a damaged card just like mine so that i can get the parts i need, but it's hard to find one! And i don't know any place where i can buy these "pieces" that I broke!

[gonzo0815]

Re: Video card MOSFETs crushed... need to replace them?

Bga is not that bad regarding current capability and cooling. usually, on those card there is an heatsink applied direcktly on the chip surface, similar like the die cooling of the older soket a Athlons. Thus i think this package is very convenient for massproduction and high current low space vrm units. But any way, on my card, there are two SMPS controler chips, wich can control up to 4 different and independent vrm /voltage section. On of those is probably responsible for the ddr ram voltages (ddr needs two different voltage levels, at least as i learned from the chip`s datasheet), the other controls the GPU voltage. From that point of view it makes not mutch sense, if those tiny chips have any own control logic. Thus i think, that the reason for their description is their very speciall desing, may be they are only intended for the very speciall applikation on gfx vrm`s.