Zotac 2080ti low 1V8 Rail

[Nick868]

Hello
I've got a zotac 2080ti with 1v8 missing, found the problem and changed U3 buck converter, C70, C81, C75, C82 and R32 with the schematic value. Now i start the gpu and i've 1,2V instead of 1,8V. I think that voltage is too low, what can i check??

[прямо]

First of all, is the Zotac using the same buck converter chip GS9216?

If it is, you should remove R33 (12.7K 1%) which is part of the feedback network that sets the adjustable output voltage to 1.8V, and check its resistance value.
You may also want to make sure that the R32 you replaced has the correct resistance value and tolerance (10K 1%)

[Nick868]

First of all, is the Zotac using the same buck converter chip GS9216?

If it is, you should remove R33 (12.7K 1%) which is part of the feedback network that sets the adjustable output voltage to 1.8V, and check its resistance value.
You may also want to make sure that the R32 you replaced has the correct resistance value and tolerance (10K 1%)

Yes, i've bought same chip on Aliexpress.
R33 measures 12,8 on the board without R32, should i remove to check better??
R32 it's 10K 1%.

[прямо]

Yes, i've bought same chip on Aliexpress.
R33 measures 12,8 on the board without R32, should i remove to check better??
R32 it's 10K 1%.

No that's not necessary. 12.8K is close enough.

What about VIN, is the chip getting the correct voltage?
Also may want to check R35 (100R 1%), maybe its resistance has gone up.

[Nick868]

No that's not necessary. 12.8K is close enough.

What about VIN, is the chip getting the correct voltage?
Also may want to check R35 (100R 1%), maybe its resistance has gone up.

VIN it's 12V.
R35 it's 1.2 ohm mounted on board. Maybe it's this one?

[прямо]

Try removing that and measure it outside the circuit.

On a side note, I don't have the same schematic.
Mine is MSI, and R33 has a different value. 2.55K instead of 12.7K.
The chip is also GS9216.

[Nick868]

Try removing that and measure it outside the circuit.

On a side note, I don't have the same schematic.
Mine is MSI, and R33 has a different value. 2.55K instead of 12.7K.
The chip is also GS9216.

It's perfect, 100 ohm.
Well i've another schematic where R32 it's 499ohm and R33 1K. I don't know how many versions there are.

[прямо]

Perhaps you can temporarily remove R33 and solder jumper wires from its pads to a 20K or a 50K multi-turn trim pot.
Adjust the trim pot to 12.7K first, then power up the card.

Then slowly adjust the trim pot again until you get 1V8 at the output.
Write down the adjusted resistance for R33, so you can replace the trim pot with a resistor.

I know that this is kind of a "hack" than a proper problem solving, but hey, sometimes you gotta do what you gotta do to make it work

[Nick868]

Perhaps you can temporarily remove R33 and solder jumper wires from its pads to a 20K or a 50K multi-turn trim pot.
Adjust the trim pot to 12.7K first, then power up the card.

Then slowly adjust the trim pot again until you get 1V8 at the output.
Write down the adjusted resistance for R33, so you can replace the trim pot with a resistor.

I know that this is kind of a "hack" than a proper problem solving, but hey, sometimes you gotta do what you gotta do to make it work

I just removed R33 and it's 10K

[прямо]

I just removed R33 and it's 10K

Well, I guess you found your problem.

[Nick868]

Well, I guess you found your problem.

I've measured voltage on FB both on U3 and U4, and both are on 0.59V. Are these values correct??

[прямо]

Yeah it is. Schematic says the Vref is 0.6V, and that's exactly what you're getting.
R33 being 10K is definitely the wrong value, because:

Vout = Vref x (1 + R33/R34)
Vout = 0.6 x (1 + 10/10)
Vout = 0.6 x 2 = 1.2

So if you want it to output 1.8V, you have to change R33 to 20K.
Vout = 0.6 x (1 + 20/10)
Vout = 0.6 x 3 = 1.8

[McWhitePink]

likely the gpu core is dead if you have a short on 1.8V

[Nick868]

likely the gpu core is dead if you have a short on 1.8V

I don't think so because the short was only on C82. I've to change R33 and try to power on. With 1.2V the GPU start and the core Is warm, but voltage Is too low and the GPU Is not detected.

[McWhitePink]

I don't think so because the short was only on C82. I've to change R33 and try to power on. With 1.2V the GPU start and the core Is warm, but voltage Is too low and the GPU Is not detected.

1.8V is also powering the VRAM, see if you can find our if any of the VRAM is damaged. better to have a thermal camera for this job.

[Nick868]

1.8V is also powering the VRAM, see if you can find our if any of the VRAM is damaged. better to have a thermal camera for this job.

So i got it finally!!
The R33 resistor was too low, i try to put a 12.7K resistor but the voltage was low, about 1.3V. So i put a 20K resistor, voltage was about 1.78V, so i reassembled the gpu and mounted it. Now it seems working and i'm testing!!

Thank you all, especially прямо!!!

[прямо]

No worries. Glad to know you got it working