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-   -   Motorola VT-71 after recap, small weird picture (http://www.videokarma.org/showthread.php?t=271885)

CJVx 08-01-2019 11:14 PM

Motorola VT-71 after recap, small weird picture
 
1 Attachment(s)
I replaced all the electrolytic and paper caps Along with the selenium rectifiers of course in this thing, the ballast tube measures correctly, and I swapped out a few weak tubes. When powered up, I have B++ at 216v, as expected, but I have this small picture that will hold stable horizontally, it will not roll vertically but it’s stretched and contorted. When ice adjust the picture wider horizontally that’s when it gets wavy on the top on the bottom. At full adjustment it will not fill up the screen left to right.

One more clue is it has the best focus with the controlled all the way to one side. I did some diligence by checking any of the molded capacitors for shorts and none are shorted.

Can someone point me in the Right direction for fixing this. Thanks.

Electronic M 08-02-2019 08:26 AM

What did you replace the 6KV caps with?

CJVx 08-02-2019 08:50 AM

I got some 6KV Wima Polypropylene Metallized film caps, in .0047uf and .0015uf.

Notimetolooz 08-02-2019 09:09 AM

For one thing it looks like some of the vertical is getting into the horizontal signal. Maybe through a common power supply connection. That probably wouldn't explain the small size.
I suppose it could be a defective CRT with broken deflection plates.

CJVx 08-02-2019 10:36 AM

Quote:

Originally Posted by Notimetolooz (Post 3213287)
For one thing it looks like some of the vertical is getting into the horizontal signal. Maybe through a common power supply connection. That probably wouldn't explain the small size.
I suppose it could be a defective CRT with broken deflection plates.

hmm i wonder if i have any of those 6KV cap connections crossed, when i acquired this set 6 or so years ago, i snipped one side the 5 of them for reasons i cant remember, and there was some minor questioning of the connections when i put in the new caps. I'll double check tonight.

CJVx 08-05-2019 07:53 AM

1 Attachment(s)
So here is the latest. I did in fact have two capacitor ends swapped, it was one from the horizontal center control with one from vert. center control, so that explains the mix of horz. and vert. Anyway, just after correcting this, i had a very short folded over picture, max about an inch tall but with a full horizontal spread. Now, after just sitting idle overnight, the picture has lost all horizontal deflection, and still minimum vertical like before. Not sure what happened for it to lose horizontal like that since nothing really changed, but i do not hear the horizontal oscillator running like i did before.

Also a clue for the vertical would be, if i hot pull V10 (vert oscillator tube) and stick it back in there quickly, i have a half second of a taller picture, (but still no horizontal at this point), when i did have full horizontal, the picture got bigger and shrunk back down to an inch.

things i have done,

I have disconnected one end of most molded caps, measured and confirmed they were still measuring good, and reconnected (i did find one that was open, but after replacing it, no change in symptoms)

Tested the sweep tubes again, confirmed they are all strong enough

swapped similar tubes around, cleaned pins and sockets...again.

Things that stand out as possible issues -
making sure grounds are good and the ground wires are all connected
look for open caps i could have overlooked

Any other suggestions?

Kevin Kuehn 08-05-2019 12:19 PM

Make sure your CRT's socket is making good contact to the Horz deflection plate pin. Although I wouldn't think that would make the horz oscillator stop running as you suspect.


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