Sansui G7000 phono input troubleshooting needed

[boardjames]

Expanding upon a previous thread about a malfunctioning selector switch (now solved):

I had my engineer father-in-law help me crack it open and run a few tests. After sliding the switch shaft back into place, the input selector switch appears to work fine. However, the phono 1 and phono 2 inputs are still inoperative. The FM, AM, and Aux inputs all work fine.

We connected a Picoscope Oscilloscope/Function Generator to the phono inputs (one at a time) and applied a 50 mV sine wave (1000 Hz), hoping to hear a tone out of the speakers. We also monitored the input signal with the O’scope. The signal was dragged down to -1.6 Volts when connected to the Sansui phono inputs. Can’t imagine that is good.

Have you seen this sort of thing before? Looks like the inputs may be shorted somehow? Any advice on what to look for or where to start?

Thanks

 

[DougBrewster]

there may be a dc level mismatch between the oscillator and phono input. Put a bipolar capacitor between the oscillator and the phono input to block the DC or better yet your oscillator may have a DC level function which you could adjust to compensate...

 

[Madman1]

Hey BoardJames,
Did you resolve this problem? I have a g7000 with the exact same issue.

 

[AGoodson]

My G701 same as a G7000 had this issue. The fix is 4 100 ohm resistors on the equalizer board that supply -30v and +30v. Either one or all 4 are bad if neither phono 1 or 2 work and everything else is fine.