Sony 28FX20U (BE3B chassis) no G1 voltage
 

All

I've come by a Sony 28FX20U (BE3B chassis) set, which runs but flashes
the standy light to indicate error code 5 (video fault) and the picture
is rather washed out.

I don't have the service manual but checked the tube base shows that
the G1 votlage is missing. I note also that the 1kV on connector CN703
is not present, but due to missing components, it's clear that it's
not supposed to be on this particular set.

The G1 voltage comes from the G1 control mounted on the tube base
(PCB C). The diode D712 meters out fine, but there is no voltage at
the G1 pins except for a negative blip when the set is first powered
up.

I suspect the Line Output Transformer is defective. It's obviously
rather tricky (dangerous) to try to examine the unrectified output
to the G1 control from the transformer, so I can't easily prove
whether it's the control or the transformer.

Any help most appreciated. Please email in any reply.

Thanks and regards,

Colin

www.video99.co.uk

Sony 28FX20U (BE3B chassis) no G1 voltage
 

Check for a low value resistor and associated diode off the LOPT, associated
with it will be a electrolytic cap rated probably 10 - 47 Ufd @ 250VDC.
Should be able to trace that source to the G2 area of the CRT Drive PWB.
"Colin McCormick" wrote in message
...
All

I've come by a Sony 28FX20U (BE3B chassis) set, which runs but flashes
the standy light to indicate error code 5 (video fault) and the picture
is rather washed out.

I don't have the service manual but checked the tube base shows that
the G1 votlage is missing. I note also that the 1kV on connector CN703
is not present, but due to missing components, it's clear that it's
not supposed to be on this particular set.

The G1 voltage comes from the G1 control mounted on the tube base
(PCB C). The diode D712 meters out fine, but there is no voltage at
the G1 pins except for a negative blip when the set is first powered
up.

I suspect the Line Output Transformer is defective. It's obviously
rather tricky (dangerous) to try to examine the unrectified output
to the G1 control from the transformer, so I can't easily prove
whether it's the control or the transformer.

Any help most appreciated. Please email in any reply.

Thanks and regards,

Colin

www.video99.co.uk