AOC E2470SWHE No power

[kalauzz]

Greetings,
I have this monitor wiht a smashed screen and I would like only to understand which problem had only for curiosity.
Opening it I found its very similar or maybe identical in power board and main board to the ASUS VW224T I repaired some days ago for a bad capacitor on the power board.

The problem: Fuse : Gone, Bridge rectifier : Gone and a strange spot circular burn on the screen panel side in corrispondence of one leg of the transformer (near the R926 Resistor).
I replaced bridge , fuse but still non life but no short circuit now.
320V in the big cap after bridge (ok) but no alternate voltage on the secondary legs of the transformer.
No visual damages, but I suspect an open resistor 1R5 value near the burnt and maybe the IC gone (??).

I m mainly curious about this circular spot, any ideas.

Regards

[momaka]

Check big resistor R903, located next to switch IC (U901). R903 should show a low resistance. If it's open-circuit, U901 is probably bad.

Also I see an overheated ground trace between J903 and U901. Because of that, check diode D901 and C908 for ESR/capacitance. R926 may be open-circuited as well, so check that too.

Use series 60-100 Watt incandescent bulb with monitor AC line when applying power to the PSU so that you don't blow any more fuses or other parts when testing.

[CapLeaker]

you need the PFC to work. The 320V needs to be boosted to ~400V.

[dick_barton]

I m mainly curious about this circular spot, any ideas.

It looks like one of the transformer pins needs to be resoldered and cause the black spot you show.

[momaka]

Originally Posted by CapLeaker

you need the PFC to work. The 320V needs to be boosted to ~400V.

There's no APFC circuit on the PSU in the pictures shown above. So 320V is correct.