Feedback goes from emitter Q501 to C525 ,ensure with dmm ,that this is correct ,not broken .After C525 to high freq pot viper ,check resistance too ,c519 to c521 connection , resistors and capacitors related to that potentiometer . Maybe c523 R539 not getting ground ?
And you said - they are "identical" - corrosion on legs maybe identical 🙂
Glad to hear you resolved it .
Glad to hear you resolved it .
After replacing of 2 potentiometers Amplifier works fine.
But left channel a little quieter than the right.
Maybe due to Q509 shorted?
But left channel a little quieter than the right.
Maybe due to Q509 shorted?
What about loudness ? Switching loudness on off now works ok in both channels ? Try to short both ,q509 q510 .Maybe balance control works only on one channel ? Also ,try to short volume potentiometers sliders ,join together both channels ,make mono temporarily , to ensure that fault is after volume control .
Try shorting channels from volume then . If you saying one channel a little quieter ,it may be even some resistors out of specs .Factory sometimes depending on amp price don't bother to make channels them identical ,just put resistors in place and solder .Need to determine now where is difference .
I would suggest you following ,to find little difference in channel sounding .Begin from end . Connect one speaker across both channels output + ,so you will hear only difference .Need to put just one channel from source to amplifier, to make true mono mode,your amplifier has mono switch ,but it don't short channels fully. You can disconnect RCA connector from one of inputs and solder wire to other channel. If absolutely identical ,there should be silence now. Decrease volume of input source many times ,increase volume knob to max , thus eliminate it from frequent disbalance of channels ,and watch if not loud .If you hear something playing ,its channels difference . Now need to find ,if its not power amplifier .Need to join power amplifer inputs together , should be silence now ,if not - need to find not identical resistance resistors in both channels .Take care on feedback resistors ,they may have on schematic like 1k , but actually one channel may have 990 ohms ,other 1005 ohms ,and thats it .If you hear bass loud ,then its capacitor bad in one channel ,need to find out which ,and replace. When you finish balance power amplifier, proceed to preamplifier ,remove joining of channels at power amp input and proceed further to tone control .I think my idea is clear .
Don't forget about the terminal rivets on pots of a certain vintage.
Congrats on the successful diagnosis!
Cheers
Congrats on the successful diagnosis!
Cheers