K7400 - B+ reading -80V??

[callanbrown]

Working on a totally dead K7400. No clicking, only a degauss sound when on a tube.

HOT is ok. Trying the lightbulb test now, getting no light and I'm getting -80VDC on the B+. Yes, negative. The B+ adjustment pot has been bypassed by a 1k resistor (by someone else) and it was working this way on location for months of not years.

I'm not particularly familiar with the K7400 so I'm wondering if anyone has come across this very odd situation.

 

[callanbrown]

Well ignore my silly comments, I was measuring at both the wrong TP and the wrong ground.

After watching a video I did the diode check on the U101 SMPS chip, which failed. I grabbed one from a spare board and the monitor is fixed.