G-7500 Phono

[dauph]

I recently picked up a G-7500. The thing looks and sounds awesome and is definitely an upgrade from my early '90s pioneer receiver that I was using.

The only issue I am having is with the phono preamp. The right channel is working and sounding great but the left channel is not playing anything. This is the same for both phono inputs (it has 2) leading me to believe that it is an issue with the shared preamp. I have had the same issue with two fully operational turntables and the issue presits when swapping the left and right inputs from the turntable. Both channels work and sound amazing for all other inputs (tape aux AM/FM)

I am looking to repair this myself if possible as money is a little tight in college. If anybody has any insight on this issue or can link me to somewhere better to post this please share.

 

[rcs16]

Either it is switch contact(s) or there is something wrong in the circuit.
Get a service manual from hifiengine & use your ohmmeter to perform a continuity test when powered off
1) Test S601a, on F-2852, check for continuity from the left phono input jacks1 & 2,switched in one of the 2 phono positions, to the junction of R101,R103
2) Test S601c, on F-2852, check from R43,C33 to terminal 15 or tape monitor1 rec jack, switching either or both, phono 1 & 2 positions.
Hopefully it is one of the above, try to clean the switch contacts with some deoxit D4, sprayed on the contacts to remove tarnish, if it is that.
If the switch contacts have continuity, low ohms <5 ohms, then you will have to measure the voltages against the schematic with power on.

 

[dauph]

I didn't expect such a targeted and specific answer so fast. If you just knew that off the top of your head I am blown away.
I downloaded the schematic from hifiengine and your suggestions for test seem spot on. I am pressed for time at the moment so this project will have to wait for the weekend but I will be sure to respond back with my findings.
Thanks

 

[rcs16]

No, it was not off the top of my head but it certainly helps to own one, serviced it and have a schematic to read from.
One thing I can say to improve it, is to upgrade those o/p bjts, but do it when you have the time and $ to do it, if the old ones lasted this long it has been babied. use these,
NJW3281G (NPN)
NJW1302G (PNP)

Good Luck and let me know how you make out.
Rick

 

[dr*audio]

A common problem with older equipment is electrolytic capacitors going bad. This causes low or no signal on one channel. If cleaning the switch doesn't work, try replacing the caps in the phono circuit. If you can read a schematic you can use a meter probe to inject hum into the circuit and probe each stage of the preamp to see where the signal is being lost, working from the output of the phono stage toward the input.