Need help on K7400 - Lightbulb test works; still clicks. No B+

If the HOT tests shorted in circuit and fine out of circuit you have a short on the B+ rail you need to find.

Andrew

When checking the HOT in circuit you will see a short from the base to emitter. This is because you are measuring across T701's secondary winding and L704 which is basically a short. The only way to check it in circuit is to place your positive lead (red) to the tab of the HOT (collector) and the negative lead (black) to ground. High resistance good, short probably bad. Still the best way to check if the HOT is good or bad is to remove and test.
 
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Make sure you have good continuity to all places the B+ goes to. Check around the flyback. Especially as the traces and solder pads can be damaged when removing and installing the flybacks.

Here are few points that I can think of off the top of my head.

Negative lead of C725
Pin 3 of flyback
Anode of D718
Collector of Q704
One side of R728

Ed
 
that can be a tricky problem to track down.

verify that you have all the correct caps in the correct location and polarity.

give the chassis a good re-flow, they suffer from lots of cold solder joints.

if your H.O.T. is good out of circuit and your bulb is good, then it is most likely something in your horizontal section shorting to ground.

if you need it fixed, your welcome to send it in.

Peace
Buffett
 
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