LCD Monitor troubleshooting

[wraper]

Well, I think a bit late but worth watching.

[TorArne]

Its dead, docs says max 600v.

Did you probe secondary of the CCFL transformer  ? Well, I warned  . Or considering blown fuse, did you probe something connected to the mains? Well, I asked for primary winding, guess you probed wrong primary as I meant inverter?
I asked for different board photo. Small PCB that sticks out of the PSU PCB near CCFL inverter transformer.

I probably did something wrong yeah
Its no problem, was a really cheap scope. (think it was 45usd)
Tried fixing it.. but there's something really wrong with it.. so going in the trash.. hehe..

Here's the correct board, probably.

[bithead9]

FYI Great resourse for LCD monitor repair:    http://www.badcaps.net/forum/
Good luck on your repair!

[wraper]

Here is schematic of this PCB. You should check highlighted signals. Measure voltage on C6 and C2. Post brightness min/max, switched off voltages. Don't know which particular brightness control input is used in this case. PWM is ON/OFF input + brightness (optional). Brightness can be controlled by PWM or PID which is analog brightness control input. If PWM is used, PID should always stay at +5V, otherwise voltage must change on it depending on brightness.

[Alex Eisenhut]

Its dead, docs says max 600v.

Did you probe secondary of the CCFL transformer  ? Well, I warned  . Or considering blown fuse, did you probe something connected to the mains? Well, I asked for primary winding, guess you probed wrong primary as I meant inverter?
I asked for different board photo. Small PCB that sticks out of the PSU PCB near CCFL inverter transformer.

Yikes, don't probe the secondary with a regular scope probe! The voltage ratings are just for DC. Even with a 1000X probe I got into trouble, there's some serious power there at a high enough frequency to derate the probe to a much lower voltage!

[Shock]

Here is a better picture of the boards. Having nice clear photos helps.

I take it that you have done the basic stuff like try different inputs to the monitor, test it on a bios screen and reset the defaults to confirm they are indeed suffering the exact same problem?

Since you have multiple of the same model can't you swap testing the CCFL cable connected from another screen? Will not work if they are in series though.

I'd be checking the ballast caps and the HV transformer as well.
Do you have a working one?

[TorArne]

DIM 3,26v
PID 1,29v

Need to connect a monitor to be able to adjust brightness. will try and do that now

Tor Arne

[TorArne]

Here is a better picture of the boards. Having nice clear photos helps.

I take it that you have done the basic stuff like try different inputs to the monitor, test it on a bios screen and reset the defaults to confirm they are indeed suffering the exact same problem?

Since you have multiple of the same model can't you swap testing the CCFL cable connected from another screen? Will not work if they are in series though.

I'd be checking the ballast caps and the HV transformer as well.
Do you have a working one?

I do have a working one at work.
The rest i have are all broken with the same fault.

I have tested reset to default and all kind of stuff.
Nothing helps.
Even the menu (without anything connected) is dim.
I have testet ALOT of caps, not found a single bad one yet.

Tor Arne

[TheBay]

What panel is in this, Make and Model?, could be driver chips on panel or mainboard is weak, I don't think its inverter/ccfl issue.

What voltages are present on mainboard from PSU?

[TorArne]

What panel is in this, Make and Model?, could be chips on panel or mainboard is weak, I don't think its inverter/ccfl issue.

Here's a picture of it

[TheBay]

What panel is in this, Make and Model?, could be chips on panel or mainboard is weak, I don't think its inverter/ccfl issue.

Here's a picture of it

I had a feeling it would be an LG Display Panel for some reason!, the boards look like LG too but no markings, awful PSU/Inverter design. Did they really cheap out on parts lol.

Can you describe the flickering, is it on the screen? or if you look behind at backlight is it that flickering?, is backlight bright when looking at the side of it? I have a feeling its Panel or scaler board.

Do you have a hot air station and/or ESR meter?

[TorArne]

Can you describe the flickering, is it on the screen? or if you look behind at backlight is it that flickering?, is backlight bright when looking at the side of it? I have a feeling its Panel or scaler board.

I dont recall seeing the flickering on other monitors i got.
Backlight dont seem to be flickering.

[TheBay]

Have you got a hot air station and an ESR meter?

The main IC on mainboard on these type of scalers sometimes get poor joints, caps are also weak.
Check all voltages going in to mainboard too.

[TorArne]

Have you got a hot air station and an ESR meter?

The main IC on mainboard on these type of scalers sometimes get poor joints, caps are also weak.
Check all voltages going in to mainboard too.

Sorry, i do not have any of that.
I do have a hot air gun thou.

Tor Arne

[TheBay]

Do you have the right nozzles? Might be worth heating up the legs on the main scaler ic, also check pcb smd fuses etc.

[wraper]

DIM 3,26v
PID 1,29v

Need to connect a monitor to be able to adjust brightness. will try and do that now

Tor Arne

Then PID voltage must increase with increasing brightness. If it does not, try to solder a ~1k resistor in parallel to R13 and see if brightness becomes normal.

[Vito_R]

BTW just noticed that you changed some capacitors. If you fix this monitor, throw those green Chengx junk away and solder original ones (suppose they were Rubycon) if you still have them, or get something better. Those Chengx are not only poorest quality capacitors but also have huge ESR. I once bought few, didn't check the brand they gave me at the local shop because they usually had Jamicon WL in stock which are green too. So when I measured, they had ESR like 2-3X bigger than general purpose capacitors with the same capacitance and voltage specifications. Moreover, they even don't write series on them, just LOW ESR which they obviously are not. There seems to be series marked on yours, but they are too tiny to be good compared to original ones anyway.

Agree get rid of those crappy Chengx caps.  Replace all electrolytics with high quality low ESR Japanese caps and you'll extend the life of your board for many years.  I like using Nichicon PW, HE, or HW series.

[wraper]

Why should he replace all capacitors if they are all Japanese except one? It unliekely to provide much longer life as CCFL or backlight transformer should die first IMO. Even if some capacitor dies, it will be only one, not bunch of them altogether.

[Vito_R]

Why should he replace all capacitors if they are all Japanese except one? It unliekely to provide much longer life as CCFL or backlight transformer should die first IMO. Even if some capacitor dies, it will be only one, not bunch of them altogether.

I meant only the chinese caps, not the ones he has already replaced with Japanese.  Those chinese caps eventually will fail one at a time if you just replace the defective ones.  Better to recap all at the same time then have to open up the monitor again when the next failure occurs.

[wraper]

Well he have wrote previously that he will put original Rubycons back. Chengx were those he replaced. Actually I haven't ever seen that crap to be present in any monitor from factory.

[Vito_R]

Well he have wrote previously that he will put original Rubycons back

I guess I missed that, sorry.

[kimi007]

Hello J have the same problem.
Rotate cables to lamps, but you must to extend it.
That will solve problem.
Sorry for my bad english.
Best regards.
Miki

[luke9511]

hello and good day all, i came across this thread while searching for a way to fix the same model of monitor as the op, i have about 4-6 of them all with the same issue there is a very faint picture, it is either very very dark or very dim and some flickering, does anyone have any ideas i can try?