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Apple Computing Products:
macOS - Desktop Hardware
Late 2013 imac 27 no power
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<blockquote data-quote="jsg68" data-source="post: 1862044" data-attributes="member: 405615"><p>Yes, but from what I can find in terms of reports of GPU problems, they aren't consistent with this no-power-at-all symptom. The reports I've seen all talk about display issues.</p><p></p><p>(Interestingly, it sounds as if it would actually be possible for a pro to replace a GPU, because reportedly, the GPU problem is actually due to heat deformities damaging the GPU solder connections, and it can be resolved by having a pro re-solder the the connections.)</p><p></p><p></p><p></p><p>I don't see any visual indication of damage, at all. Not on the power supply, not on the logic board, no where. Whatever has gone wrong seems to be invisible.</p><p></p><p></p><p></p><p>Just one: LED 1 indicating trickle power. At this point, I've completed the entire troubleshooting procedure from the service manual for this condition (only LED 1 lit). Assuming the replacement power supply I received is actually functioning properly (and therefore, serves as a "known good power supply") there would seem to be no explanation left except for a problem with the logic board. (That's how the troubleshooter ends---if it's not be resolved, it's the logic board.)</p><p></p><p></p><p></p><p>Yeah, but it appears it may actually be just one pin that goes from inactive to active, distinguishing between on and off. I'm seeing 12V on about half the pins of both the original and replacement power supplies, which suggests to me that they probably are working. i.e., either they're working, or they both have some power-up related failure (e.g., not passing through the power button continuity signal, or not properly responding to the power on signal back from the logic board). Otherwise, it seems the problem must be on the logic board side.</p></blockquote><p></p>
[QUOTE="jsg68, post: 1862044, member: 405615"] Yes, but from what I can find in terms of reports of GPU problems, they aren't consistent with this no-power-at-all symptom. The reports I've seen all talk about display issues. (Interestingly, it sounds as if it would actually be possible for a pro to replace a GPU, because reportedly, the GPU problem is actually due to heat deformities damaging the GPU solder connections, and it can be resolved by having a pro re-solder the the connections.) I don't see any visual indication of damage, at all. Not on the power supply, not on the logic board, no where. Whatever has gone wrong seems to be invisible. Just one: LED 1 indicating trickle power. At this point, I've completed the entire troubleshooting procedure from the service manual for this condition (only LED 1 lit). Assuming the replacement power supply I received is actually functioning properly (and therefore, serves as a "known good power supply") there would seem to be no explanation left except for a problem with the logic board. (That's how the troubleshooter ends---if it's not be resolved, it's the logic board.) Yeah, but it appears it may actually be just one pin that goes from inactive to active, distinguishing between on and off. I'm seeing 12V on about half the pins of both the original and replacement power supplies, which suggests to me that they probably are working. i.e., either they're working, or they both have some power-up related failure (e.g., not passing through the power button continuity signal, or not properly responding to the power on signal back from the logic board). Otherwise, it seems the problem must be on the logic board side. [/QUOTE]
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Apple Computing Products:
macOS - Desktop Hardware
Late 2013 imac 27 no power
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