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jd3rdcoast
Super Member
Try feeding a signal directly to the Amp In jacks in back to isolate the amp and make sure the problem does not eminate there.. Can use a phone and patch cord. Keep phone audio turned all the way down until you are ready to test. Then raise it up. If all quiet then issue is coming from the preamp section or controls.
Did you recently install long screws into the feet? Like if you removed a wood case and used the long screws? Or recently have the front cover off for service?
Check the solder lugs of the Volume pot for cold/cracked solder joints.
Did you recently install long screws into the feet? Like if you removed a wood case and used the long screws? Or recently have the front cover off for service?
Check the solder lugs of the Volume pot for cold/cracked solder joints.
This unit has been recapped (except) FM board. New transistors installed, rebuilt power supply also.
No matter what input is selected the problem still persist, no signal.
No wooden cover, metal bottom and casing, I tried re-installing them and no difference.
The positive of the main bridge rectifier H009 has 0.5 VAC residual. It could be a ground loop or some noisy transistors...do not know. When you touch the potentiometer metal stem (volume) the buzzing goes way down. Also it is an intermittent problem.
No matter what input is selected the problem still persist, no signal.
No wooden cover, metal bottom and casing, I tried re-installing them and no difference.
The positive of the main bridge rectifier H009 has 0.5 VAC residual. It could be a ground loop or some noisy transistors...do not know. When you touch the potentiometer metal stem (volume) the buzzing goes way down. Also it is an intermittent problem.
jd3rdcoast
Super Member
Go back and check all your work. Check proper orientation of all new components.
What transistors were replaced and with what?
Still need to cut the problem in half by verifying amp operation independent of Pre-amp side. So you know where to focus your efforts.
Then use a scope and trace audio signal to where noise is picked up.
What transistors were replaced and with what?
Still need to cut the problem in half by verifying amp operation independent of Pre-amp side. So you know where to focus your efforts.
Then use a scope and trace audio signal to where noise is picked up.
The amplifier does work and sounds very very good. TO-92 on preamplifier were replaced with modern KSC1845 & KSA992. Phono board was also retrofitted with KSC1845.
The power supply was rebuilt using MJ series, the amplifier modules P700 have all original transistors. DC Offset & BIAS are spot-on. Will try to debug separately.