K7000 b+

fritz

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Donor 2019
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Any thoughts on what would cause the B+ on a K 7600 to be 145 V? I did a CAP kit, changed IC2 and IC3 which fixed the vert issue, fly back and voltage regulator. It went from 160 V down to 145 V after I changed the voltage regulator. The HOT is not shorted. I have a good picture which is odd to me with such a hide B+.
 
We're going to need some over/under pics of your chassis. Have you done a lightbulb test? This will isolate the power section so you can verify your VR is working properly:

 
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I don't understand why lightbulb tests on linear power supplies in K7000s have been normalized here. the B+ circuit on a K7000 is AC in, a bridge rectifier, a filter cap, and a resistor (R103) which turns 160V DC into 123-130V DC. it's nothing like SMPS on a K7400 where that test would be beneficial to perform if you have a bad chassis. this is probably something I've seen before in the past and fixed, but given that this is my job and the diversity of things I fix, I can't remember everything I do. I mostly fix pinball or heavy logic issues on game boards, last K7000s I did anything with were over a month ago. lol

much of the problems with K7000s are in the resistor connections because these monitors have been in service for over 30 years and even professional monitor repair outlets don't even so much as redo/resolder the yoke or signal header pins. or if you're Atlas or PNL you just barbecue about 16 solder pads just to make the job more difficult for the next guy (me in this case).

unfortunately I can't help further without it being in front of me, and I'm not good at looking at even high detail pictures. the B+ circuit is pretty simple though. if you haven't seen this video give it a whirl:
 
I do the lightbulb test after verifying all the components in the power circuit. I want to see ic4 working properly before powering up the deflection section to avoid barbecuing the HOT.

Now granted I also check all the regular stuff in the deflection circuit too, but it's worth the extra time to me as a sanity check.

I'm not anywhere near @mecha 's level which is why I need the methodical approach! 🙇
 
Subconsciously to prove my point I just missed a shorted d20 working on a k7000 a min ago. Fortunately I was doing a lightbulb test and using a circuit breaker! Double checking my work, I replaced it an now we have a perfect 130vdc :)
 
Update on my B+ issue. After reflowing more pads. I now I have 123 V. Didn't see any suspect pads, but there must've been something.
 
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