Re: Sharp LL- T17A4-B lcd Monitor

Franc Zabkar wrote:
On Thu, 12 Jun 2008 12:04:02 -0500, jakdedert
<jakdedert@xxxxxxxxxxxxx> put finger to keyboard and composed:

Bought from the 'E' place for cheap. Reported symptom: video comes on and fades out. Figured it was high ESR smps caps.

Actual symptom: backlight comes on, image consist of random horizontal lines, which eventually--after some intermittent vertical scrolling--settle into a very nice image. Takes like two minutes to warm up. Shutting the monitor down for some unknown time starts the process all over again. Continuous viewing yields a stable image with good resolution, brightness and linearity. Shutting down for short periods is not problematic.

There is only one HV (100 @ 400v) cap in the ps. ESR is .46, which I assume is within tolerance. Other caps in the ps also seem fine.

This presents so like a classic cap issue (needs to warm up), that I'm going to next pull the video board and check caps there...possibly get some freeze spray and see if I can duplicate symptoms that way.

Reality check: any problem with the above procedure, or experience with this particular monitor? Any suggestions as to where to go if the above doesn't produce a dx and fix?

Thanks as always,

jak

FWIW, that monitor came with a 3-year warranty.

If that is not an option, then I'd be hooking up your scope to the
horizontal and vertical sync inputs and following them through. It may
help if you told us which chips are used, eg Genesis Microchip.

Have you considered that the video source may be just outside the LCD
monitor's range? I sometimes find that a 75Hz refresh rate is right at
the limit before the monitor blacks out. Try a safe 60Hz refresh rate.

What about the OSD? Is it stable? Pull the RGB cable and watch the "No
Signal" OSD window, or whatever your monitor reports.

- Franc Zabkar

Thanks Frank, for your attention.

It contains a (socketed) Winbond W78E56P-40. I pulled up the data *** for that, but it's beyond my experience to decipher how this generic processor is employed in the circuit. The other large scale (100 or so leads) chip has a logo that looks like a backward capital 'N' with numbers MST9111. Google drew a blank on that one.

Changing video resolution makes no difference (refresh was initially 60 Hz anyway). The OSD, when accessed while 'in symptoms', is just a blue smear up the entire height of the display. Any video input to the display is likewise; all columns and no rows. Each column of pixels is uniform in color from top to bottom, although that color changes with the video content. Occasionally horizontal bands will appear, either a lighter or darker shade...sometimes only a pixel wide, other times wider.

(I wonder if I could record and post a short video somewhere?)

For the last day or so, I've not been able to get any sort of legible display. I hooked it up to a spare computer, on screensaver, next to my desk, hoping to catch it actually working...turn it on occasionally for short periods.

You might be able to tell that I'm not too familiar with the innards of lcd displays <g>. This board appears to have several layers, making visual tracing of the circuitry difficult, although I should be able to trace continuity from the input pins to the various sm devices.

I'm afraid I'll be almost totally occupied with other business for the rest of the week; but I'll eagerly check back here for any insight into this....

Thanks again,

jak
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