AMD HD 6990 old beast very low 3.3 V resistance

[aysat]

Hi guys,

i have a hd 6990 which has 2 gpus in a pcb. the odd thing is the card works but 3.3V line has various resistance readings. mostly 0.7 ohm and sometimes i read 1 kohm. both cases the card runs just fine but 3.3 V line becomes very hot due to low resistance,i guess. especially dc to dc buck convertor on the riser. it reaches 95 C degrees in 5 minutes. a good working card makes it run at 45 C degrees usually. what should be my next move ? inject voltage from 3.3 V to see what is causing extra heat and check with thermal cam ?

any suggestions will be appreciated. i can upload photos if needed.

[aysat]

Re: AMD HD 6990 old beast very low 3.3 V resistance

no ideas?

[mon2]

Re: AMD HD 6990 old beast very low 3.3 V resistance

Never worked on video cards before but could the issue be dry / old heatsink compound on this video card? Can you confirm the required chips are being dissipated of the heat properly? There are some great current heatsink pads (T-Global, Taiwan) and heatsink pastes that are worth trying to reduce this heating.

Otherwise, would say that you have possible stale caps due to the very low resistance on the 3v3 rail. Can you compare the resistance against a known good video card?

[aysat]

Re: AMD HD 6990 old beast very low 3.3 V resistance

heatsink is fine. a good working card has more than 250 ohms

[momaka]

Re: AMD HD 6990 old beast very low 3.3 V resistance

Hi guys,

i have a hd 6990 which has 2 gpus in a pcb. the odd thing is the card works but 3.3V line has various resistance readings. mostly 0.7 ohm and sometimes i read 1 kohm. both cases the card runs just fine but 3.3 V line becomes very hot due to low resistance,i guess. especially dc to dc buck convertor on the riser. it reaches 95 C degrees in 5 minutes. a good working card makes it run at 45 C degrees usually. what should be my next move ? inject voltage from 3.3 V to see what is causing extra heat and check with thermal cam ?

Try the video card directly into a motherboard without a riser and see if 3.3V line going to the card is still dropping. If it is, check the RAM VRM / MOSFETs, as those sometimes get power from 3.3V rail (not always though.) There should also be a linear regulator or two that take 3.3V and convert it to lower voltages required for starting up the GPU chip (hence why if you disconnect power cables from the video card, it can still show a message on the screen, telling you that the power cables are disconnected.)

If you do have a thermal camera, that could actually help see if anything is getting abnormally hot on the video card PCB... so give that a try as well.

BTW, RAM Vdd/Vddq VRM should have a resistance of around 10 to 200 Ohms (varies, depending on the type and number of RAM chips used, as well as manufacturer.) 0.7 Ohms sounds more like a reading for the GPU Vcore(s).