[TechAssist] Toshiba VCR, M-725C, power supply blown
- From: Gary McCartney <number63@xxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Fri, 15 Mar 2002 16:07:39 -0500
This VCR came in with a minor problem and now the power supply is
killed.
Problem was that during play, if FF was pressed, then PLAY pressed
again, the picture would switch between clean video and video full of
severe lines (such as tracking off), about every two seconds. This did
not occur when VCR was cold.
I found that if I applied freeze spray to D831 in power supply, that
this symptom would clear up. With no schematic, I decided to replace
this little glass diode with an ECG552, figuring it was a B+ rectifier,
fast switching. Plugged unit in and it was completely dead, no display
and no functions at all. Unplugged and check circuit board for solder
splashes and shorted parts, found none. Put original diode back in and
still dead. While measuring PS voltages, fuse blew and chopper
transistor has very hot and shorted. I managed to get voltages off
chopper first. C= 165V, B= 0.43V, E= 0V. Also found 0V on cathode of
D822 B+ rectifier in secondary. I have since checked transistors, caps,
etc. in PS. and I don't find anything wrong.
Just wondering if D831 is supposed to be a zener? The symbol on the pcb
is that of a regular diode. numbers on the diode are: A 3 3
Does anyone have a schematic of the power supply?
--
Gary McCartney
McCartney Electronics
7134 Fife Rd, RR 7
Guelph Ontario Canada N1H 6J4
Fax: (519)821-1530
email: number63@xxxxxxxxxxxxx
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