Look at the part number on the RAM. Pull up the datasheet for that particular RAM. Search for equivalents. You likely won't find modern made equivalent chips, so you'll have to source it new old stock, or used off other hardware.

GF4 series, that's where they started using vram in BGA packages, right?

Seeing that you have a hot air rework station, have you tried simply reflowing the existing vram chips? Way simpler than replacing BGA packages with hobbyist equipment, and definitely worth a shot at least.

If you haven't already, and it does the trick, install chip heatsinks afterwards. The source of the problem is usually that the different heat expansion of the PCB and the chip substrate exposes the solder joints to mechanical stress. At some point, they break. Keeping the working temperature span as small as possible alleviates that.

I believe they are BGA chips yes. Good call on reflowing them I havent tried that yet so it's certinly an option. What sort of temperture am I aiming for ? is 220c ok like for the GPU.

I'll look into some heatsinks too, theyre cheap and readily available so worth a try.

Thanks !

Sipha wrote on 2021-09-12, 15:14:

I believe they are BGA chips yes. Good call on reflowing them I havent tried that yet so it's certinly an option. What sort of temperture am I aiming for ? is 220c ok like for the GPU.

I'll look into some heatsinks too, theyre cheap and readily available so worth a try.

Thanks !

Yeah, it's not like you have anything but a little bit of time to lose from trying, you'd take the same risks replacing the chips 😀 Also, you could try taxing the card until it starts artifacting again, and then push down hard on each chip in turn. If/when the artifacts go away, you've probably found the specific chip causing the problems. Would save some of that time.

Well, the required temperature depends on equipment and solder type. If you can preheat the PCB properly, 220 deg C might be enough. If you can't, you'll probably have to go higher. If you know for sure the solder is leaded, you could use lower temperatures (would guess it's not though if the joints broke in the first place).

Personally I wouldn't bother with proper preheating procedures for that job. The chips are thin and small. Would simply apply some no wash tacky flux around the chip's edges, heat the PCB close to 200 deg C from the back side with the rework gun (keeping the card oriented horizontally with the chip upwards), and then heat and hold the chip at say 230 deg C for a minute, before letting it all cool down.

I'm somewhat of an amateur in this field though, you'd probably find better advice than mine on Youtube etc.

I'm of course not talking about airflow temperatures here by the way, but actual PCB and chip temps. An IR thermometer helps tremendously 😀