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KDS Rad-7bk LCD Monitor Distortion

This 2004 LCD monitor is nearly working. The onscreen menu is functional, clear, and sharp.

But the computer image is distorted. It's like every other scan line is moving back and forth at something like a 30 to 60 Hz rate. Auto-tune does not affect the problem. Again, the onscreen menu is clear and sharp while the image behind it has this interlaced distortion.

There were two bulging electrolytics (1000uF@6.3V, 470uF@16V) on the control board. Replacing them made no noticeable difference. There are plenty of smaller electrolytics, but none obviously bad.

There's one online reference to the problem, but no useful solution:

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Any suggestions? Thanks!

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Warren Block * Rapid City, South Dakota * USA
Reply to
Warren Block
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I have since replaced all of the larger electrolytics (100 uF and above) with no improvement. This monitor gets its power from a 12V DC adapter that plugs into the back of the VGA connector. Video noise happened both with 12V from a computer power supply and from the AC adapter.

Here's difference between the computer image and the onscreen menu:

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And here's the controller board. Capacitors with a black mark are ones that have been replaced:

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Warren Block * Rapid City, South Dakota * USA
Reply to
Warren Block

If this was my project, I'd put a (good) scope on the various RGB signals on that VGA connector, and see what they look like. Trigger on a vertical sync pulse, and move down the scan lines...

I've got to wonder if you are running it at a scan rate that is not directly supported by this monitor, too. Have you tried different scan rates (both vertical and horizontal)?

Reply to
PeterD

Unfortunately, no scope, good or otherwise. Capacitors seemed like a good guess because of the periodicity of the problem and the two obviously bulging ones. The controller PC board has a little bit of heat darkening behind the regulator at the upper left. After removal, those two small 10 uF caps near it read as 2 to 2.5 uF on my Fluke 79.

There's also some darkening behind the main chip in the center, and the heatsink compound was only contacting the heatsink at the edges. Fixing that didn't help, either.

I've ignored the inverter so far because it worked. There are a couple of small caps on it, and I may replace those on the idea that the interference is some kind of feedback from the inverter.

Yes, and autotuning the monitor. It displays other resolutions--as well as it can--and scan rates up to 75Hz. It's consistent and works well... as long as you don't need to see it too clearly.

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Warren Block * Rapid City, South Dakota * USA
Reply to
Warren Block

Working from largest downwards, I replaced all of the electrolytic capacitors on the controller and the inverter board. Testing of the removed capacitors showed that many had deteriorated to half or even a tenth of their marked value. Yet nothing improved until the last five on the controller. These were three 10 uF, 25V and two 22 uF, 16V near the toroid inductor. One of the 22 uF was definitely bad.

And that cleared up the distortion. The monitor seems to be fine now.

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Warren Block * Rapid City, South Dakota * USA
Reply to
Warren Block

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