AOC LCD recap

[pentium]

I got an AOC LM729 which after a few seconds or so kicks out the backlight but still displays a picture so I opened it up and while I did not see any bulging caps I still pulled two Elite 1000uf, 16v and two hermei 470uf, 16v caps and will be repalcing them tomorrow. Yes there were two more hermei caps on the inverter board but they were both rated 150uf, 25v and four TL caps on a board between the inverter and video board rated 16v 470uf and again, not one of these caps were bulging. Should I replace them all anyways? I'm heading into town later and if I don't buy the caps this trip I won't be able to get into town for another week.

[pentium]

Re: AOC LCD recap

managed to revive two other LCD panels but of course, the AOC panel still switches the backlight off after a few seconds. >:/

[EGuevarae]

Re: AOC LCD recap

I got an AOC LM729 which after a few seconds or so kicks out the backlight but still displays a picture so I opened it up and while I did not see any bulging caps I still pulled two Elite 1000uf, 16v and two hermei 470uf, 16v caps and will be repalcing them tomorrow. Yes there were two more hermei caps on the inverter board but they were both rated 150uf, 25v and four TL caps on a board between the inverter and video board rated 16v 470uf and again, not one of these caps were bulging. Should I replace them all anyways? I'm heading into town later and if I don't buy the caps this trip I won't be able to get into town for another week.

Replace them, you are there anyway. Or at least buy the replacements just in case. You can't have too much caps anyway...

[pentium]

Re: AOC LCD recap

You are gonna have to wait until next week as I went into town today.

[pentium]

Re: AOC LCD recap

BuMP.
Recapped the board and it fixed nothing.
then yesterday I find another wrecked AOC monitor I salvage the boards from and still, the backlight goes on for a bit and then switches off.

[Bobdee]

Re: AOC LCD recap

BuMP.
Recapped the board and it fixed nothing.
then yesterday I find another wrecked AOC monitor I salvage the boards from and still, the backlight goes on for a bit and then switches off.

Sounds like Inverter or CCFLs, check out the inverter transistors and the solder joints on on inverter transformers
Pictures would help
Bob

[Toasty]

Re: AOC LCD recap

Agree. Bad tubes -or- shorted transformer winding would draw excess current & will trip the inverter protection circuit.

[Bobdee]

Re: AOC LCD recap

BuMP.
Recapped the board and it fixed nothing.
then yesterday I find another wrecked AOC monitor I salvage the boards from and still, the backlight goes on for a bit and then switches off.

Also found this (new to me)
A utube video on a fix for a Blue Ceramic cap on inverter with on/off problem
http://www.youtube.com/watch?v=jQeEy...eature=related
bob

[PlainBill]

Re: AOC LCD recap

Also found this (new to me)
A utube video on a fix for a Blue Ceramic cap on inverter with on/off problem
http://www.youtube.com/watch?v=jQeEy...eature=related
bob

Not a ceramic. He mentions a 16 volt, 1000uF capacitor.

I'm not sure how much faith I would place in this video. He was replacing one of the film caps in the inverter. This appears to be the same inverter circuit used in the Dell E172FPb / E173FPb monitors. There are a couple of electrolytics in the inverter, and the value he referenced is definitely an electrolytic cap, but the one he appeared to be changing was a film cap. Now if that cap was bad, it would screw up that half of the inverter.

PlainBill

[Bobdee]

Re: AOC LCD recap

Not a ceramic. He mentions a 16 volt, 1000uF capacitor.

I'm not sure how much faith I would place in this video. He was replacing one of the film caps in the inverter. This appears to be the same inverter circuit used in the Dell E172FPb / E173FPb monitors. There are a couple of electrolytics in the inverter, and the value he referenced is definitely an electrolytic cap, but the one he appeared to be changing was a film cap. Now if that cap was bad, it would screw up that half of the inverter.

PlainBill

I do agree
It was the Blue Film cap in between the transistors, my mistake calling it a ceramic
I have seen the Grey box type fail there with visual signs but never the Blue type, I do not recall ever reading about this Blue cap failing in the Monitor forum before so I think its one to keep in mind
Bob

[wkydvdfan]

Re: AOC LCD recap

I have the same problem and have recapped the board with no success. Anybody have a suggestion? I'm new and I too saw him replace the film cap. Is this standard film cap or is their a part number like the capacitors?

[PlainBill]

Re: AOC LCD recap

I have the same problem and have recapped the board with no success. Anybody have a suggestion? I'm new and I too saw him replace the film cap. Is this standard film cap or is their a part number like the capacitors?

Which 'Same problem'? Two seconds to black? No backlights? You mentioned you recapped the board. What brand and series of capacitor did you use?

Please post pictures (top and bottom) of the power supply / inverter board. I hate pretending I have a crystal ball.

The joker on the Youtube video was pulling a switch. The cap he described was an electrolytic; the one he replaced was a film cap. (Not too cool).

For the record, within the past year the following causes for the 'two seconds to black' problem have been identified:

Bad transformer.
Glue around HV caps
Bad CCFL
Bad wiring on CCFL
Bent pin on connector.
Wrong replacement caps.
Bad transistor
Bad capacitor

PlainBill

[wkydvdfan]

Re: AOC LCD recap

I'm working 12 hour days and I'll get pics as soon as possible!

Yes 2 seconds of display then no back light.