05-05-2013, 10:50 AM
Connect your VTVM probe to the junction of R19 and R20. This is the output of the detector rectifier which supplies the AVC voltage, isolated by the 47K resistor R19. This point should connect to the Phono-Radio switch M10. Ground connection should connect to B- ( negative of filter caps). The AVC voltage is negative, so set your VTVM accordingly.
KEEP IN MIND that the B- circuit ground is connected to one side of the AC line so use an isolation transformer, otherwise the case of your VTVM may be hot with 120 VAC. If you have a battery powered DVM, this may be a better choice as it is battery powered and more likely isolated with a plastic case.
KEEP IN MIND that the B- circuit ground is connected to one side of the AC line so use an isolation transformer, otherwise the case of your VTVM may be hot with 120 VAC. If you have a battery powered DVM, this may be a better choice as it is battery powered and more likely isolated with a plastic case.
