Re: T922 Power Supply Problem

Mlynch001
 

On Sun, Jul 7, 2019 at 01:37 PM, @DC912 wrote:


Hello.

With power on, the power lamp does not light or blink.

I measure negative 700mv at the -8 test point on the power supply board.

I measure positive 700mv at the +8 test point on the power supply board,

The secondary on the power transformer for the 8v supply tests good.

I measure 82 volts at the +100v test point on the power supply board.

With the power supply board in the scope, resistance between -8v test point
and ground is 180 ohms, 200 ohms between the +8v test point and ground.

With the power supply board removed from the scope, resistance between the -8v
test point and ground is 35k ohms, 20k ohms between the +8v and ground.

I also removed the vertical and horizontal boards to check the resistances on
the 8v and -8v rails to ground on those boards. None of the rails on the two
boards measured lower than several kohms.

Any suggestions on where to go from here would be greatly appreciated.

Thanks. Dave.
I would check the items listed in the service manual under Service Information. U742 is part of both +8 and -8 power supplies. Service manual also mentions several other transistors. -8V check Q772-774-776 +8V Check Q752-754-756.

--
Michael Lynch
Dardanelle, AR

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