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I’ve been refurbishing 2011 27” iMacs for a while now and I’ve come across 2 logic boards with a strange symptom. Both of them cause the GPU to run at 100MHz instead of the normal 680MHz. Everything else on these boards functions properly. I’m thinking there’s a voltge or current problem but I don’t know what to check.
Any clues?
Is this a good question?
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@notenufgarage - I think you damaged one of the two ferrite beads near the sensor connectors. Review this question: GPU/CPU working at 50%
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What does Diagnostics tell you?
by Dan
Nothing out of the ordinary. The GPU operates at full speed on other logic boards. Only benchmarks like Luxmark, Unigine or Cinebench indicate there is a problem.
by tpluth
I'm talking about Apple diagnostics. Restart the system and press the D key
Mac startup key combinations
by Dan
Yes. AHT did not report any errors.
by tpluth
I'd be curious to know what the GPU temperature is on the affected motherboards and a known-good motherboard.
by Steve
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