Traynor TS120B bass amp

[robgrif]

hi all
I have a traynor bass amp TS120B I am trying to repair
The amp powers up ok but the output is garbled mixed with 60 cycle hum
The xlr output from preamp alone is distorted and hums
I replaced TL071 and TL072 in preamp
there is a switching IC TL604 that i did not change as I could not locate one to purchase
Transformer output is 36 volts AC steady
The amp rails should be 50 volts + and -
however the test on the output of the bridge rectifier gives me plus 50 volts
and minus 32 volts
I changed the rectifier but the readings are unaffected
Output Transistors were removed and ohm meter tested and seemed to check out correctly
I think this is a preamp problem but not certain of that
however I am puzzled at the low minus voltage reading at the negative rectifier output
any thoughts on a possible cause for the amplifier problem or cures ?

thank you in advance

regards
robgrif

[g1]

The filter cap for the -50V is probably bad. Otherwise something is loading down the -50 supply. If you measure AC at the outputs of the rectifier you will probably see much more AC on the -50 than on the +50 side.

[robgrif]

traynor ts120b bass amp

The filter cap for the -50V is probably bad. Otherwise something is loading down the -50 supply. If you measure AC at the outputs of the rectifier you will probably see much more AC on the -50 than on the +50 side.

thanks for the tip you were right on the mark
replaced the cap and amp came back to life
voltages now are correct
thank you for help
regards
robgrif