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This is the preamp section of one channel of a tape deck.

This is the preamp section of a channel of a tape deck for which one channel is working and one is not. Swapping all the components between the channels does not affect which channel is working correctly, so presumably the components are all functional.

Measuring the voltages across the IC chip on the good channel, the values are as in the schematic, while the values for the chip on the bad channel values are zero for pins one through five and around one for pins six and seven.

If there are no faulty components in a circuit, what else could cause voltage irregularities across an IC chip?

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    \$\begingroup\$ The chip itself is likely to be faulty. \$\endgroup\$
    – Andy aka
    Commented Jan 16, 2021 at 13:21
  • \$\begingroup\$ I put the chip in a separate identical circuit and it worked so it doesn't seem to be faulty. \$\endgroup\$
    – cheaterpushups
    Commented Jan 16, 2021 at 13:23
  • \$\begingroup\$ well then the circuitry around is clearly causing the problems, since you've precluded the IC. \$\endgroup\$
    – Marcus Müller
    Commented Jan 16, 2021 at 13:24
  • \$\begingroup\$ Reveal the bad voltages you mentioned in your question please. \$\endgroup\$
    – Andy aka
    Commented Jan 16, 2021 at 13:25
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    \$\begingroup\$ Check if R27 is still in place with the correct value and the right voltage at teh other end of it. \$\endgroup\$
    – user16324
    Commented Jan 16, 2021 at 13:59

1 Answer 1

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There is a fault in the power distribution of the 12.9V dc supply.

Measure the voltage on that pin, with/without the IC and tracing to its source should pinpoint the fault.

measure Voltage on green trace and look for ~ 12V~13V. enter image description here

It could be a cracked via.

It's a vintage ssssssony

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  • \$\begingroup\$ Thank you much for the answer. Not sure if it's too specific for the OP but it would be personally helpful if you could elaborate on how to trace to the source. \$\endgroup\$
    – cheaterpushups
    Commented Jan 16, 2021 at 14:04
  • \$\begingroup\$ Follow the coloured trace road with a DMM and measure the voltage' \$\endgroup\$
    – D.A.S.
    Commented Jan 16, 2021 at 14:32
  • \$\begingroup\$ By the way, it's an rs-m22g; you were very close. \$\endgroup\$
    – cheaterpushups
    Commented Jan 16, 2021 at 14:48

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