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Posted: 8/22/2004 12:21:48 AM EST
[Last Edit: 8/27/2004 12:19:10 AM EST by prk]
After a power outage was fixed, this monochrome security video display unit was bad. The high-pitched whine isn't heard, and the 'picture' consists of a single 1/16 " vertical line right up the center of the screen.

No schematic, but a little research makes it sound like the horizontal deflection isn't, uh, deflecting.
Also suggested somewhere was that this could point to the high voltage supply. Haven't yet looked up 'horzontal trigger', but that's next.

Anybody got ideas? I have the vendor's address & may have to buy a schematic.

The flyback transformer has been id'd.

And how best to discharge any lurking high voltage?
Link Posted: 8/22/2004 4:37:19 AM EST
Link Posted: 8/22/2004 5:55:54 AM EST
get rid of it and buy new one. relatively cheap for b/w monitor.


meat
Link Posted: 8/22/2004 10:42:03 PM EST
The cap that looks like it leaked is 1000 microfarads, rated 35v, near the flyback transformer. The board is brown and the areas that look like they leaked don't really contrast.

Only slightly bigger physically are two 22 microfarad 200v on the small board mounted on the neck, but there is no sign of leakage there.

I was surprised that these are as small physically as they are, even though it's a 12" solid state set.
Was expecting to see one the size of my thumb.

Link Posted: 8/23/2004 10:10:07 AM EST
It's called a collapse. Either vertical or horizontal collapse. Caused by a dry cap. Find the dry cap and replace. Very, very, very common problem.
Link Posted: 8/23/2004 10:16:30 AM EST
Link Posted: 8/23/2004 10:21:19 AM EST
[Last Edit: 8/23/2004 1:28:42 PM EST by goodmedicine]
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GM
Link Posted: 8/23/2004 10:28:30 AM EST
Link Posted: 8/23/2004 10:37:40 AM EST
I would dispose of the offending monitor, for a hundred bucks or so, it ain't worth risking injury or worse death over a couple of $10 worth of capacitors. but if you are fairly knowledgeble about HV power supplies then I would go for it.
Link Posted: 8/27/2004 12:20:26 AM EST
[Last Edit: 8/27/2004 12:47:32 AM EST by prk]
Having waited almost a week for the HV to bleed off, I dove deeper.

Had to map all the connectors needing to be unhooked to get the main circuit board out. Other than that, it was pretty easy except for the time I wished I had a third hand, one to release the tabs holding the front to the base while also supporting the base and the front with the CRT.

Went to inspect the capacitor, but stopped when it didn't seem to be shorted.

Looking at the bottom of the main circuit board, I saw a nearby spot where there was evidence of a burn where a lead came through the board.

Solder was pretty much gone, the hole for one component lead was about 2 X the normal diameter, and the solder pad was pretty much vaporized away.

Turning the board back over, you could see that it was a 180 microhenry choke with obvious distress to the leads, but miraculously, it was still conducting according to my meter.

After resoldering the coil to each lead (it was making contact but I wanted to give it the best connection), it was possible to resolder it on the bottom, bridging with solder the gap between the lead and the PCB trace.

Then I put some expoxy around the enlarged hole and also on top at the base because physically it wasn't as strong (with the eroded hole ) as before.

After partially reassembling, I plugged it in and turned the switch on. The narrow vertical line has been replaced by a full raster ( no input ) complete with date & time from the internal clock!!!

Letting it run for an hour or so, there were no odd smells, noises, or smoke.

Thanks to all of you guys for the help. This was a favor for a storeowner I know.

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