13” K7203 monitor - wavy picture/interference

[Spicules]

Got this unit dead; checked the pcb and there was a cluster of caps with one bulging in the corner.

Replaced some caps in that area, and powered on. High pitched squealing noise made me think its the flyback.

new flyback does not change, so I do a complete cap kit and go over the traces for loose connections etc.

I do see a transistor near the flyback on a small heatsink that is so loose, it felt like it would fall out of the board.

So I redo a bunch of connections, and do some jumpers (the pads were burned on the transistor)

After that, it will power on and display raster. 

I can get to to display video with my Test pattern generator, but there's slight, small horizontal lines in the video like as if you were watching a VHS and the tracking was a little off.

There's horizontal "interference" lines is the best I can describe.

I've already tried adjustments, but this doesn't look like an adjustment to me.

I read that C008 (471uf/1kv) causes problems with these and my cap kit didn't include this non-electrolytic cap.

I’ve ordered that cap for now and that’s my only lead at the moment.



Anyone ever fix this issue?

Link to video of problem:


https://imgur.com/a/IZlqPqs

[FUNWIZ]

Not sure what all caps you have replaced as you’re kind of vague that you replaced some of the caps. Did you replace the 220µF 400 V cap C005?  Also unplug your degaussing coil during testing to make sure it is not staying on.  C101 and C102 100µF at 160 V. TP1 121V. TP2 24V. TP3 12V. TP4 8V. JP301 16V. U101 pin3 5V.  GL

[Spicules]

I went through the caps and checked for loose connections etc, and found no issues; then I swapped back to the OLD Flyback, and that got rid of the problem.  Going to let it run for a few more hours and see if it stays.

This was the one from arcadepartsandrepair.com ; maybe it is better for the 19" and not the 13"?

But to clarify - I replaced all electrolytic caps, except the BP cap at C14 (1ouf 100v) that the kit did not come with.

Also went over loose connections and replaced flyback that did not fix and maybe even caused an issue?

[FUNWIZ]

Could be a bad flyback or they gave you the wrong one, they both use the same one.

[Spicules]

Now intermittently works.  Stuck it in the cocktail I intended it for, and it was working great for a few days.  Then it would stop.  I'd put it on the bench and it would work... back in the machine...stop working ... and so on.

checked this on the bench when this happens, it has ~ +23v at TP2 , 12v at TP3 , 5v at P100 , ~7.6v at TP4  the correct testpoints and B+ TP1  is around 150 (much higher than the 121 needed)

The other voltage test points seem on point, and I'm thinking its in HV shutdown but I don't know what's causing it.

[Spicules]

Shelving this one;  Put a 19" K7000 chassis on this 13" tube.  Pretty much drops right in (I had to add a pin to plug the CRT ground to the neckboard) and works great now.

Will revisit this chassis another day.