Keep digging you will figure it out. Just a few ideas on test gear...Insulate the dmm probe with quality electrical tape except for the tip. Beware of how much voltage your subjecting the scope to and scope probes in general. You can be seriously shocked by trimmer access holes, gaps, etc. Buy an isolation transformer and plug the scope into it. Also pick up some desoldering wick before you bust the board traces. Let us know what you discover.
Audio Research D70 repair
Hallo again ! I have been busy for a while but are now working again with this D70 . The regulator with TIP 41 , D40k1 Darlington transistors are feed from a TLO 71 OP.
There are 338 VDC to the screens but unfortunately just one volt lower out from the emitter of TIP 41 . ( Should be 7-8 VDC lower as Hifigeek have mentioned ) . I though the TIP 41
was bad and soldered in a new one ..... but no , it was OK.
Now I suspect that TLO 71 . How can I find the wrong component ? Guess I need some advice here . The 24 V zener only has about 21 V over itself .... Can it be some 2uF/450V cap which is bad ... so its ringing , oscillating ?
I have a scope so I guess I can check that ... I´m very careful when I measure the voltages in this circuit ... trying not to slip with the testprobe .... To me it seems that both powertransistors are fully open ....? Thanks for some advice .... its not easy to desolder / change components in this amp because it is soldered on both sides of the board. Regards Stewen
There are 338 VDC to the screens but unfortunately just one volt lower out from the emitter of TIP 41 . ( Should be 7-8 VDC lower as Hifigeek have mentioned ) . I though the TIP 41
was bad and soldered in a new one ..... but no , it was OK.
Now I suspect that TLO 71 . How can I find the wrong component ? Guess I need some advice here . The 24 V zener only has about 21 V over itself .... Can it be some 2uF/450V cap which is bad ... so its ringing , oscillating ?
I have a scope so I guess I can check that ... I´m very careful when I measure the voltages in this circuit ... trying not to slip with the testprobe .... To me it seems that both powertransistors are fully open ....? Thanks for some advice .... its not easy to desolder / change components in this amp because it is soldered on both sides of the board. Regards Stewen
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