Horizontal Red Lines... Baffled!

Toomasu

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These red horizontal lines appear randomly for a while then vanish. It seems to happen when I first turn the game on for about 10 minutes or so, after that time, it doesn't reappear.
I am not clear on the problem...
I checked all the caps (especially those around the heatsinks) they all check out ok.
The b+ is stable.
I can't find any web page describing this particular issue anywhere.
Once it stops, the picture is clear, this monitor was almost brand new with zero burn. The flyback is dialed in properly.
I can't figure this one out. Voltages are solid, there's no cut traces, grounds are good. I have tried adjusting the red pots on the neck board.
Solder joints all seem to okay.
I'm not sure of the identity of the chassis, I was told it is a Wells Gardner. I'm not particularly fond of working on these (I have in the past with little success)
Advice from someone who knows more than "hey, check voltages and caps" the simple stuff is no problem, I'm under the impression this is more than an easy fix.




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IMG_3026.jpgNew Golden Defender Monitor (5).jpgNew Golden Defender Monitor (7).jpg
 
You could also swap the red color drive transistors with either green or blue to see if the issue changes colors. That will point to the component you swapped as being bad. If you remove the drive transistor and its still outputting red then its a board or tube issue. Almost looks like blasting to me but not quite. That would point towards a short in the red gun of the tube.
 
Kinda screams "bad connection".
I would suspect the vid connector/header on the game board first. IDC or solder-joint.
But agree, need to define if a logic board issue or a monitor issue. Or, as stated, the connection between the two.

I've seen this on my Robotron. And it was the vid harness. YMMV
 
Defender dates to the early 1980's. If you haven't had a cap kit done, you may want to do one. This looks like something that could be caused by a failing cap, which is allowing AC to leak into the signals, and then "reforms" as it heats up.

It will get worse and worse over time until it doesn't reform, and then it will stay this way.
 
Kinda screams "bad connection".
I would suspect the vid connector/header on the game board first. IDC or solder-joint.
But agree, need to define if a logic board issue or a monitor issue. Or, as stated, the connection between the two.

I've seen this on my Robotron. And it was the vid harness. YMMV
could be this. jiggle the signal harness at the MPU and monitor ends to see if it influences it.

otherwise...

Defender dates to the early 1980's. If you haven't had a cap kit done, you may want to do one. This looks like something that could be caused by a failing cap, which is allowing AC to leak into the signals, and then "reforms" as it heats up.

It will get worse and worse over time until it doesn't reform, and then it will stay this way.
it's a K7203. they do all kinds of dumb things. I would encourage wiping the RGB cutoff pots on neckboard. you'll need a precision flathead or plastic alignment tool to spin them back and forth. contact cleaner also encouraged.
 
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