Electronics > Repair
Laptop repair 20v rail intermittently getting pulled down to 5v
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Rik_Koningen:
I'm slowly learning more advanced repair, it's already my job but I'm becoming more advanced as I go. Right now I'm stumped by one laptop at work. The 20v rail is getting pulled down to 5 volt at fairly regular intervals. Too quick for a multimeter to show but the scope shows it just fine. Once every 2 or so seconds it drops for about 150 micro seconds. Laptop acts like it gets no power in general the whole time. No voltages present outside of that 20v. And as it's on longer it starts dropping deeper and deeper down to 3v after half an hour. Also no components are getting detectably hot in the process at all.

Tested with mobo fully removed from the chassis and with everything unplugged. Same result. No "regular" shorts are present on the board at all. At this point this is a worthless laptop I'm mostly looking at to learn so I've as much time as needed to figure it out (while no actual priority work exists, or in my breaks anyway). What could be causing this? I've got a feeling it's my battery management chip since voltage exist before it but not after. But I mainly want to know why this happened and how on earth we get at that weird intermittent not quite short circuit that pulls my 20v down. I kind of don't want to just replace the chip before knowing why or at least having an idea so if anyone knows I'd greatly appreciate any insight. Multiple other power sources also tried to same results.
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