PYE P123BQ: Receiver Intermittently dead

The symptoms in one of these receivers were that at times the set would work perfectly on both M.W. and L.W. but at other times it would be totally dead.

The first check was made on the push pull class B output transistors (TR5, TR6 in Trade sheet 1311), by measuring their emitter, base and collector currents but these were all in order. Then attention was turned to the driver stage TR4, where it was found that there was no base current.

The fault was finally traced to the base decoupling capacitor C26 a 50uF electrolytic, which had an intermittent short-circuit , replacement cured the fault.