25" K7000 Full Vertical Collapse - Abnormal Cause Fix

zenomorp

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Got a couple 7000s in for repair. One with full vertical collapse. Another with partial collapse. Started with the one in full collapse. Gave it a full look over and the first thing I noticed was a missing fuse. Checked all the normal power components and they were good. I also found numerous bad solder joints. Most notably on one leg of R101 and a cracked joint on a horizontal yoke header pin. Fixed those along with re-flowing everything that needed to be. Nothing else looked amiss so I installed a fuse, put it on a tube, and fired it up to verify the discrepancy. Yup. Full vertical collapse. To save time, I went right to IC3 and verified I was getting the 26vdc reference. That ruled out the flyback, R91, R92, D13, and D14. Made sure none of the legs of IC3 were shorted to ground that shouldn't be. That means the IC should be good. Verified R80 was not open (it was reading 5.9 ohms when it should have been around 3.2 ohms). The 5.9 reading is for the 19." This is a 25." This chassis had some rework and I'm assuming someone looked up the rating in the manual and it shows 5.9, but that's for a 19." I also found the H.Hold pot was broken (had to physically move it to see the break) and the V.Pos pot just spun in a full 360 when adjusting it.

I kept poking around in the circuit because none of those issues alone would directly cause a full vertical collapse and I ended up finding the C53 poly cap was destroyed along the top. Looked like someone used a pair of cutters and just cut off the top. Don't know if that's what happened or if it blew it's top for some reason. It was dead shorted. Replaced it with one from a donor board, replaced the H.Hold pot and the V.Pos pot, and fired up the chassis again. Success. Deflection came back but it still looked partially collapsed. It was simply a matter of adjusting the 50/60hz pot and the V.Size pot. But I discovered I could not get full height. There was around 2" on top and bottom that I couldn't get to fill. This was caused by the 19" 5.9 ohm R80 being installed instead of the 3.2 ohm for the 25." I installed a 3.2 ohm R80 setup (I had to use a 2.3 and 1.2 setup in series to get 3.2 in circuit because I didn't have a 3.2 on hand)...and I had full deflection again. The image is a bit wide and I have the width coil adjusted all the way down, but this is being tested on a U5000 yoke, so there's not need to troubleshoot that.

This was a little bit of a crazy one, so I just wanted to share. Don't think I've ever seen a bad C53 before. If I have, it's been too long for me to remember. If there is any strange fixed to the other 7000 with the partial collapse, I'll report on that too. Thanks.
 

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Love the repair as always; i've never seen the solder mask just falling off like that!
 
Love the repair as always; i've never seen the solder mask just falling off like that!
it can happen. when I worked in Texas a large percentage of the games were obviously stored in not-climate controlled barns for 20+ years. the amount of rust and green stuff was incredible. factor in also games operated in water parks, the chlorine does some disastrous stuff. when you take into account Ken Graham wisdom that they were only meant to live for about 3 years it makes more sense. what we're doing is literally the impossible. back to the main point though, I had to fix many K7000s there and I saw all kinds of whatever with stuff flaking off and breaks everywhere. the only thing I can't do is anticipate when flybacks are going to crap out, otherwise they're kind of like Fort Knox after I get done.
 
The second 7000 had a bad IC2 and an open D25. Had 26vdc at pin 8 from the flyback on IC3, but nothing at pin 5. That was caused by an open D25. Replaced D25 and the partial collapse was better after that, but still partially collapsed. IC2 ended up being bad. After replacing IC2, full deflection came back. That took a long time to figure out. Decided to make a video recapping (pun intended) what the solution was to both of these for those who are better visual learners with a demonstration of the bad IC2 at the end...

 
I've seen the c53 and c54 cap short and cause vertical collapse exactly one time. It took me awhile to figure it out so I made a YouTube video, I can link to it here if it's ok with zenomorp to supplement the topic for future readers.
 
I've seen the c53 and c54 cap short and cause vertical collapse exactly one time. It took me awhile to figure it out so I made a YouTube video, I can link to it here if it's ok with zenomorp to supplement the topic for future readers.
I would like to see it
 
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