Explain muting relay circuit in C-4

[GasMan]

I recently bought a C-4 "fixer upper" and can't seem to get it to close the muting relays. Before I undertook this task I got an original printed service manual and frankly would be totally lost without it. Basically, TR-621 doesn't come up to -12 volts on the collector. Only makes it to -6. Everything going to the four transistors that are in this circuit seems OK (if you consider -19v where the schematic says -12 OK). Any magic hints? I've gone blind checking solder connections and cleaning up the Deoxit it was bathed in. Before I sign out...I replaced the lamps and they work fine. Got 14v, 80mA with 10" leads from Ken's Electronic Supply in Kalamazoo for $1.96 ea. Look like Yamaha parts. Thanks!

 

[avionic]

PM sent..Replace the e-caps and diodes including the zeners in the relay driver circuit.For D318 use two 1N4148's in series.When you get this pre squared away it should sound great.

 

[GasMan]

Replaced the caps and zeners in the muting circuit and now this thing sings! What they say about the C-4 is absolutely correct! Thanks to Dave for his sage advice!

 

[avionic]

Good job..! I too have bought bulbs and belts at Ken's. Also AK'r here on AK -- dgwojo is the man to see about lamps.:yes:

 

[Martin.Ca]

Don't forget the 2sc458's at TR511, TR512, TR513, & TR514 ...

 

[avionic]

Don't forget the 2sc458's at TR511, TR512, TR513, & TR514 ...

And TR619-622 in the headphone amp..2SC458's are know trouble makers that frequently get real noisy .Replace with KSC1845's.