K7000A Half of Image has a Problem

WAGDAG

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I have been working on a K7000A this weekend and almost have it licked with the exception of one issue. The top half of the image seems to be drawn twice...kind of. There are horizontal lines across the top half at all times, but there is something else going on that can be clearly seen on the cross hatch screen. The top half has solid white lines across but the dots are also drawn twice. when I adjust vertical size (remote board) or adjust 50/60hz POTs, the bottom half adjusts perfectly and the top half expands vertically as it should, but the second "layer" on the top half also gets taller / shorter at a different rate. I can't adjust it to lay on top of the primary cross hatch as seen in the pic.

I picked this up on Ebay so I do not have any history.

- Installed full cap kit and reflowed most of the chassis and the entire neckboard.
- Replaced green drive POT (green was missing)
- Removed and straightened out the three neckboard transistors that were crushed and repaired lifted pads.
- Swapped both IC1 and IC2 with a parts board I had kicking around; no change
- Tried chassis on another tube/yoke combo; no change

Looking over the schematic, I tried to check for continuity between each pin on both IC's and the next component downstream (look for open traces) and everything seems to be making good connection.

Not sure if this info is helpful - I found incorrect value caps at C56 (22uF) and C57 (47uF). Both had 100uF 160v caps installed. Also found C21 had leaked and rotted a leg off which may have been one of the causes for it going into shutdown prior to the cap kit. Could this have taken out something else? Why would someone install caps with values so far off?

Can someone please point me in the right direction as to where I can look for potential problems or perhaps explain what components come into play that I should be testing?


Thanks for any suggestions. I would really appreciate some advice.
 

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You have a "vertical foldover" symptom. Usually caused by any one of the following:

Bad vertical output IC (part number does matter, there were 4 different ICs used during the run).

Bad vertical height/size trimpot.

Bad vertical hold trimpot.

Bad electrolytic capacitor in the vertical output circuit.
 
Thank you very much for the info Mr. Layton. I really appreciate you taking the time to try and help me out and point me in the right direction.

I swapped the vertical IC3 (AN5521) which happened to be the exact one on my parts board and it made no difference.

I checked all of the vertical POTS out of circuit and two of them were slightly questionable so I replaced them with new ones. I also picked up a replacement vertical IC while at the store (NTE cross reference) since I had no idea if the spare had worked.

- Tested wires for continuity / resistance between the remote board and chassis. Found
one that was connected to VERT SIZE barely hanging on by a couple strands. Repaired
that and now all are about .5 ohm

- Went over the vertical section looking for open trace, more reflow
- Found C51 to have a very high ESR (37 ohms) and replaced it
- Tested several resistors that are between the IC and the remote board
- Tested D25, 50/60 pot, and C48 out of circuit
- I swapped the remote board with a known working one.

The issue persists and looks the same. I had hoped to post positive news that could help someone reading this thread in the future, but I can't seem to get the job done. I may just send this one off to someone that actually knows what they are doing to get repaired.

Wish I could be there when the guy finds the root cause in under 2 minutes and throws his head back and just bursts out into roaring laughter. Oh, you know he will. He will be so amused at my oversight to the obvious that he will set up a conference call to his brethren at the Secret Society of Monitor Repair Dudes to share the story. If your phone rings next week and it's Buffet, Chad, Dokert, Ed, MKL, Paul, Peter, and Tron on the line, you will know what it's about. That's how it will roll out in my mind :)

All kidding aside, I just wanted to say thanks for the help and if I do find out what's up with this thing, I will update. Have a good day...


You have a "vertical foldover" symptom. Usually caused by any one of the following:

Bad vertical output IC (part number does matter, there were 4 different ICs used during the run).

Bad vertical height/size trimpot.

Bad vertical hold trimpot.

Bad electrolytic capacitor in the vertical output circuit.
 
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