NotTaR of Television Sets : Dead TV with periodic tweet-tweet, flub-..  
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Dead TV with periodic tweet-tweet, flub-flub, or low-low voltage

A TV which appears to be dead except for a once a second or so tweet or flub usually indicates an overload fault in the power supply or a short in one of its load circuits. In some cases, the low voltage (including B+) will just be reduced to a fraction of their normal value as a result of an overload on one of the outputs - usually the main B+.

This may be caused by a shorted rectifier in the power supply, flyback, or even the yoke, but check the the loads first. Wait a few minutes for the filter caps to discharge (but stay away from the CRT HV connector as it may retain a dangerous and painful charge for a long time), use an ohmmeter across the various diodes in the power supply. Using an ohmmeter on the rectifier diodes, the resistance in at least one direction should be greater than 100 ohms. If it is much less (like 0 or 5 ohms), then the diode is probably bad. Unsolder and check again - it should test infinite (greater than 1M ohms) in one direction.

Summary of possible causes: