Mar 10, 2018, 1:04 AM
Post #5 of 37
Ah.., The rest of the story.
Re: [jts1957] Mitsubishi CS27201 repair
[In reply to]
I was testing the various supply voltages and had found all seemed good but the tube kept turning off (Horizontal voltage drive OFF.) I had tested the +5, +12 on the standby side as OK, and the hot side voltages checked out as well, the
Then, being a bit of a novice with CRTs, I accidentally shorted out the primary 130 volt to the "common tie point" return. Replaced the DC side 2A fuse and started over with the supply voltages, the regulated 12 and 9 supplies, would turn on but shut down again.
The H (B+??) voltage was measuring 163 V instead of 130, so I started questioning the STE3230 Vreg, and found that the return load resistor, a 2.2ohm 15 watt wirewound had opened as well as the fuse.
I got that fixed with a replacement from MOUSER After this, the H B+ supply read 130.5 volts (nominal) but would not turn on the hot side supplies again.
Hunting through the schematic, I found the X-Ray Prot shutdown. I found a tip in the Misc Adj. section regarding testing with R521 out of the circuit, disabling the X-Prot input.
This worked as indicated and allowed the CRT side to power up. The CRT lights up, and Audio powers up, but the supplies turn off again after exactly 10 seconds.
The CRT lights VERY BRIGHTLY, indicating that the X-Prot circuit was actually doing its job.
So, here I am stuck for the moment.
What ELSE turns off the secondary supplies? (Needs to be unplugged to be able to repeat..,) The manual also mentions using a variAC to test at this point.
What to test next?