This symptom descriptions based on the ICl multivibrator is working properly, should check the public primarily audio circuits.

IC1 and aim at measuring foot high 4.44V,V3 base is a high level, the V3 has been conducted, but relay j does not move, its contacts are not closed, the Bell does not ring because of the radio. After the power scrutinize V3, R6 and D5, relay components such as j, turns out D5 forward and reverse resistance only 150 ω, obviously damaged, resulted in relays not functioning. D5 (1N4004) replace the circuit returned to normal.


Situation such as this is rare in actual repair of V3 (9013) damage are more common relay contact j is also possible erosion, maintenance should be paid attention to. Normally closed contact input signal alarm, alarm work through VDD voltage V1 added to the ICl, so V1 increased chance of damage, maintenance pay special attention to.