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Old 01-14-2022, 11:16 AM   #1
dicky96
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Default Zotac GTX 780 3GB DDR - missing/broken component. Indentify?

HI guys, does anyone have one of these Zotac GTX 780 3GB cards and can tell me what this missing resistor value is?

It's the timing resistor Rt for the Vram VRM PWM controller so the value is important.

It's going to be in the several hundred K ohm range and you should be able to measure it OK in circuit if you have one of these cards, as it reads completely open with the resistor missing.

Alternatively a boardview or schematic would help

I have the Gigabyte GTX 780 schematic (attached) which has the same PWM controller (RT8811A) and that has 384K in this place on the schematic but is a different circuit as it also has a 47K resistor and 0.1uF capacitor here which my board does not have

The RT8811A datasheet typical application (attached) shows 500K Rt on pin 9 and does not have the 47K but has 1.0uF in this circuit

If i put the wrong value I will have the PWM controller running at the wrong frequency (380K->500K is about 100KHz different) and I imagine that would be a *bad* thing to get wrong

Cheers
Rich
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File Type: jpg 7803.jpg (518.8 KB, 18 views)
Attached Files
File Type: pdf GV-N780OC-3GD-2.1.pdf (1.01 MB, 18 views)
File Type: pdf RT8811AGQW.pdf (372.4 KB, 10 views)
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Last edited by dicky96; 01-14-2022 at 11:18 AM.. Reason: pics
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Old 01-25-2022, 12:03 PM   #2
dicky96
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Default Re: Zotac GTX 780 3GB DDR - missing/broken component. Indentify?

Someone on my YT channel identified the value of the missing resistor, he had the same card and measured it for me. It's 383K, same as on the similar Gigabyte Schematic

https://www.youtube.com/watch?v=z6BhFafIPro
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