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Old 10-02-2021, 06:27 PM   #16
ohren
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Join Date: Mar 2015
City & State: Sweden
My Country: Sweden
I'm a: Knowledge Seeker
Posts: 59
Default Re: Dell 2209wa - momentarily blinks every two seconds [ Video + Audio + Service Manu

Thanks for sticking with me and for taking the time to look up the data sheet. I would have attached it if I'd thought ahead. I didn't see your reply until I returned to report my findings but I think I basically did as you're suggesting:

I tried the ghetto mod for a day, but I knew it was stupid to put a bandaid on without knowing where the problem was, so I left the bezel off. Good thing I did, because the chassis got abnormally hot and the problem reappeared.

I opened it up tonight again and measured, and my conclusions were:

1. Fuse resistor FR851 is blown.
2. Diode D856 is shorted.

...which were confirmed by removing them both. They can be found in the circuit diagram by a text search in the manual in the OP. They're close to each other, topologically.

I checked the other fuses and diodes I could find, and I can't seem to find anything else curious about the circuit. I'm debating whether to be satisfied with that the failure of D856 was what caused FR851 to blow. Or could it be the other way around? I'm open to suggestions if it's obvious that the failure of these two also should've taken some other component with them.

Interesting that the monitor continued to be usable for hours despite this. I read up on things as I went along, but I don't have an eye for what role the diode had (in series with an NTC thermistor). Is it inrush current limiting?

Anyway, the blown fuse resistor seems to have cut off the PFC MOSFET's drain, suggesting that... no PFC was happening? That would explain where all the heat came from I suppose (my understanding of AC is limited at best, but that's what I took away from reading about PFC). Am I getting close?

Well, this is more fun than gluing a heat sink to an IC like an idiot

Last edited by ohren; 10-02-2021 at 07:29 PM.. Reason: Corrected fuse connection
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