Untitled Document
Title
M504
Classification
Service Tip
Symptom
Speaker Relay turns off intermittently :
Reason
Defect in components:
Solution
With aging some units will develop a failed components in power supply area.
If all the test with the amp seemed normal and speaker relay shuts prematurely, check for defective C708. It is important to keep the power supply voltage at 13VDC or close.
Q701 pin 2 and 3 are definitely <20mv. Pin 7 is held at 0vdc. Pin 8 should be at least 1.3vdc.
When measuring any of the channels please use the respective ground for the individual channel. Although the two power amplifier ground may be referred to as ground, they are not connected directly. The ground between the two L+R amplifiers is established through D435,D436,D437,and D438.
Within the amplifier C405 and C407 can sometime go bad.
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