Weird - K7000 keeps blowing the HOT

modessitt

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We've seen this problem before - with a new flyback being bad.

Well, I've tried THREE new flybacks - including one that works on another chassis just fine, and I still keep blowing the HOT.

Some background - this chassis was rebuilt, put into a cab, and delivered. It worked fin for a couple weeks, then suddenly had no picture. I went out and swapped in another chassis and it's been fine since.

So, today I needed another working 19" K7000, and I figured to see what happened to this. Found the fuse blown and the HOT shorted. Interestingly, C36 showed as shorted while the bad HOT was in, but not when it was out. I replaced the HOT and the fuse, found no other issues, and powered up. I got about a second of HV, then nothing. B+ reading about 12.8vdc. Fuse was still good, but HOT was shorted. Swapped in a C36 from a known good chassis, put on a new HOT, and tried again. Same thing - shorted HOT after about a second of HV.

So - what's killing my HOT? I've already checked the D18, C38, C36, flyback, Q10, D12-15, VR, R103, D19-22, IC2 - and haven't found any shorts that should account for this. Also see no solder bridges or anything.

As I'm under a time crunch, I'll probably just rebuild another chassis I have here and let this sit again, but I'd like to know what's up...
 
Thats going to be one of those bastard chassis you end up robbing other parts from :D

Might sound bad but once your into one without an obious issue youll spend more on parts chasing the problem than the chassis is worth half off the time. I usually deligate those to parts chassis
 
unplug the neck board or atleast isolate pin 3 with the 123VDC at P202 and see if you still blow the HOT.
 
I have about a dozen 19" k7000 chassis that came in a big box from an ex operator. I would assume all have problems, but most likely simple problems. I only need to keep maybe 2 or 3 of them for spares, so if you need a few,l et me know.

I have a 25" probably with the same problem. It ate to HOTs.
 
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