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Radeon 9800 Pro - repair

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First post, by Retronerd878

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Need help with a Radeon 9800 Pro repair.
The card doesn't post and motherboard beeps as there is no GPU detected.
Installed a PCI video card along side the Radeon and ATI bios flasher doesn't detect any ATI card.

Took out the thermal camera and the top FALCO coil stands out. You can touch it for like 4 seconds and then you feel the need to take your finger off of it. The bottom one is warm, not hot.
Measured the voltages on both sides of the inductor and the top one measured 0.12V and 0.04V and the bottom one measured 0.08V and 0.04V. See picture attached.
I'm guessing there is problem with the power delivery. Do i need to take off the nearby heatsink and check the components underneath?
Any ideas?

Reply 1 of 13, by tehsiggi

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So the part you are looking into is part of the GPUs power delivery (VDDC). It's main actor is an SC1175, it's a dual rail switching regulator that uses both the 5V from the 4Pin connector and 3.3V from the AGP slot.
L1 (lower one) is for the 3.3V to VDDC converter part, L2 is for the 5VEXT to VDDC converter part.

Can you first check the resistance of VDDC against GND? (measure resistance from C81 or C82) - it should be around 12-24Ohms. Having them getting hot sounds awfully like a short somewhere.

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Reply 2 of 13, by Retronerd878

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Yup, they are all shorted. C80, C81, C82 have 0.4 Ohm resistance. Also the SMD electrolytic next to them as well C732

Reply 3 of 13, by tehsiggi

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Uhh ohh.. not good. Well.. its probably not the caps that are shorted. Can you check with the thermal camera what else gets hot?
On VDDC there isn't much. Mainly the GPU and it's decoupling caps on the back.

If there is nothing standing out and you feel adventerous: remove the silver heatsink (either making it warm or very cold, your choice) and then the FETs below. If the short remains, it's pretty likely the GPU is shorted.

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Reply 4 of 13, by Retronerd878

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I compared the thermal profile with a working card that I have, and I saw that on the working card the most hot components on the back are the gpu core and the ram chips. On the bad card those are room temperature i guess.
Went ahead and took of the small heatsink and desoldered the 4 FETs underneath. Short on the caps is still present.

Reply 5 of 13, by tehsiggi

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Retronerd878 wrote on 2026-04-26, 09:38:

I compared the thermal profile with a working card that I have, and I saw that on the working card the most hot components on the back are the gpu core and the ram chips. On the bad card those are room temperature i guess.
Went ahead and took of the small heatsink and desoldered the 4 FETs underneath. Short on the caps is still present.

Crap.. Unless one of the ceramics is shorted, this sounds like the GPU being dead.

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Reply 6 of 13, by Retronerd878

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Any idea which ceramics are on the VDDC line?

Reply 8 of 13, by Retronerd878

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Yeah I took them all off and no improvement. I'm guessing this one is dead.
Anyway, my other "working" Radeon 9800 Pro I just realized that it's not really working that well. It boots into windows xp no problem. No artifacts. If I try to install drivers, it freezes up. If I try to run 3dmark 2001 with windows xp drivers I get black screen.
What seems to be the problem?

Reply 9 of 13, by tehsiggi

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Retronerd878 wrote on 2026-04-26, 11:16:

Yeah I took them all off and no improvement. I'm guessing this one is dead.
Anyway, my other "working" Radeon 9800 Pro I just realized that it's not really working that well. It boots into windows xp no problem. No artifacts. If I try to install drivers, it freezes up. If I try to run 3dmark 2001 with windows xp drivers I get black screen.
What seems to be the problem?

Check voltages and for good measure run R3MEMID. Not every memory controller fault result in immediate artifacting.

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Reply 10 of 13, by Retronerd878

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Where do i check for voltage?

Reply 12 of 13, by Retronerd878

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Blue 1.68V
Pink 2.7V
Green 1.4V
Yellow 2.65V

R3MEMID passed all tests. I think i need to do a clean install of Windows XP as the drivers for geforce 4 were previously installed. Maybe it was a software issue.

Reply 13 of 13, by tehsiggi

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Retronerd878 wrote on 2026-04-26, 16:42:
Blue 1.68V Pink 2.7V Green 1.4V Yellow 2.65V […]
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Blue 1.68V
Pink 2.7V
Green 1.4V
Yellow 2.65V

R3MEMID passed all tests. I think i need to do a clean install of Windows XP as the drivers for geforce 4 were previously installed. Maybe it was a software issue.

Good news. Give it a shot.

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