Compaq CO1075 LCD With Green Tint

[bgavin]

This is my first LCD disassembly.

The monitor is still working, but static images on the screen have an animated appearance, like the pixels are alive and chattering about. Booting the machine shows the normal black POST screen as very green.

The two-part board has three CapXon 330uF/25v and two 180uF/25v of unknown parentage on the smaller daughter board. The daughter board has two transformers and appears to be the high voltage board. The primary board has the wall-wart and VGA connector inputs.

This was mostly an exercise in lookey-see rather than attempting a repair. I'm just curious if bad caps could cause the above symptoms, if if the cause is deeper in. I know zilch about display service techniques.

[PedroDaGr8]

Re: Compaq CO1075 LCD With Green Tint

Did you try a different video cable? or by POST do you mean the monitors own post screen (if it has one)? A bad video cable can cause a color shift, while the moving pixel phenomenon can be caused by a dirty analogue signal, see a long video cable that goes near some other power circuitry and you will see what I mean.

[PCBONEZ]

Re: Compaq CO1075 LCD With Green Tint

The smaller board with xfmers is the inverter for the back-light.
It is a high voltage board.
A color shift usually indicates a problem in the inverter.

The other problems sound like the video section which has nothing to do with the inverter except maybe sharing a power supply.

Yes bad caps could cause those problems in either board.

My experience is with LCD's is 99% fixing laptop screens and with those (don't say it!) I'm a Black-Box Tech. I just replace the whole inverter. Don't fix'em. They are too small for my eyes.

If you jingle Davmax he is good with inverters.

.

[davmax]

Re: Compaq CO1075 LCD With Green Tint

Typically the back lighting tubes work or don't. Lamp or inverter. One lamp can go the other still OK and leaves part of screen dull. Colour problems need swapping in another screen to check if cable or graphics card is the problem. If it proves to be the monitor then the video/ colour processing PCB is more suspect than back lighting. This can be affected by cap problems.

[bgavin]

Re: Compaq CO1075 LCD With Green Tint

I replaced this defective screen in a client machine with a new flat panel. For convenience sake (hidden wiring), I used the same analog VGA cable on both displays. The problem is confined to the failing Compaq unit. The new Dell screen looks great, and on the same cable.

The unknown 180uF caps are on the inverter board with the transformers. The CapXon caps on the primary board.

[PCBONEZ]

Re: Compaq CO1075 LCD With Green Tint

What I tried to say before is that I think it has at least two separate problems and at least on each in the inverter and the video section.

A green or red tint is usually an inverter problem.
Bad power to the tubes.
Much less often but it could be bad tubes.

The jittery image doesn't have anything to do with the backlight circuit (where the inverter is) so that's a separate problem on the video board.

.

[davmax]

Re: Compaq CO1075 LCD With Green Tint

That input interests me. How do back lights go green? Being fluorescent they are UV that causes the glass coating to flouresce, usually a colour determined by the coating. what experience did you have where this happened?

[kc8adu]

Re: Compaq CO1075 LCD With Green Tint

the inverter wont cause color shift.
failing ccfl tubes are often pink or orangered when they are cold.
the mercury is tied up in the electrodes and phosphor.
with no reserve due to laws about hg content we now see this type of failure.
goes for standard fluorescent tubes too.
used to be cathode or phosphor wearout were the normal failure.