VP930 unstable red chanel?

[shagg]

Hi,
Many years ago I solved a recap issue simply by lurking around here, (and doing a full mobo recap!) so thanks everybody for your posts!

I now have a Viewsonic VP930, (has been fixed about 4 times under warranty!) which has developed an unstable red chanel (I think). Damm you Viewsonic!

This manifests itself as if values for say, gamma, on the red chanel, were being constantly adjusted up and down. Sometimes display is too red, sometimes not enough red. Sometimes perfect and stable for a while, (2 minutes). Seems worse in hot weather. Also a lot of flickering on certain web pages.

This is not my graphics card or cable as I am using same with another lcd at the moment..

I am looking for advice on how to diagnose and fix..I suspect caps on inverter? Looking at PSU board, logic board and inverter board, no obviously bad caps (no swelling), but I do not have test equipment to determine, other than cheapo multimeter..

Any advice is much appreciated!

[delaware74b]

Re: VP930 unstable red chanel?

The first thing that comes to mind (red tinge, flickering) is the CCFL's are at end of life. The date code on the right side of the logic board is 2006 revision, making it a 5-year old monitor.

[jsog]

Re: VP930 unstable red chanel?

If it was an inverter problem, the backlight would be a problem for all colors, not just red.

Have you tried DVI instead of VGA or vice versa?

It looks like the power supply caps have been mostly replaced with Panasonic. Probably worth replacing the last three (including C7). It's not likely that a power supply problem would affect one color more than others, but not impossible either.

The little caps on the processor board could be bad. If you're really determined, checking those for ESR might be worthwhile. Or just replace them all. Depends on whether it's worth it to you for a monitor that's been trying to fail so hard for so long.

[kc8adu]

Re: VP930 unstable red chanel?

reseat/clean the lvds cable.
seen them get fouled and cause this type of intermittant.

[shagg]

Re: VP930 unstable red chanel?

The first thing that comes to mind (red tinge, flickering) is the CCFL's are at end of life..

No I don't think it is this...I am familiar with red tinting, actually my spare, a VP201b is just like that, as was my old powerbook g4 laptop display...seeing the world through increasingly rose tinted specs!

My current problem is usually shown as a lack of red, though it can go the other way, it is most notable on colours which should be purple, but are displayed as cyan..

The flicker is on certain moire pattern and pages with textures similar to these. Sometimes faint tiled patterns in cyan occur in areas which should be white..I will try and get a photo..Generally the display looks as if it is being massively compressed, colours occuring in 'gradients' if you know what I mean.. Similar to a bad dvi cable connection..All connections on the boards look OK..

Have already tried new cable, dvi and d-sub..I guess I could recap it all and see..

NB. Viewsonic don't send you your original back on repair, they just send out a refurb model from their vast collection of failed and refurbed ones, so the history of the unit is a mystery..

[shagg]

Re: VP930 unstable red chanel?

reseat/clean the lvds cable.
seen them get fouled and cause this type of intermittant.

Thanks..stupidly didn't think of that, only checked that they were nicely in place! I am always haveing to clean off sim card contacts, so I will give this a go and report back if success!

[jetadm123]

Re: VP930 unstable red chanel?

1) Try measuring the voltage outputs of the power supply at the wiring harness, which typically are 12-14V and 5V.

2) Measure the output of the voltage regulator on the logic board, which I believe is the 3-terminal device with the adhesive label on it marked "A".

[Behemot]

Re: VP930 unstable red chanel?

Have you solved it?