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Technics SA-5760 Relay clicks in, but no sound

J

Jludowise

New Member
Just picked up a technics sa 5760. Everything lights up, the meters move, and the relay clicks in but I get no sound at all. I've already cleaned all the switches and tried multiple inputs. Fuses all seem to be good too. Wish I could disconnect the preamp from the amplifier on this thing. Thanks in advance for any help.

Jacob
 
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Thanks, painttoad. This unit was recapped (minus the tuner board) by the previous owner, who owned an audio repair business. I'm wondering if it's a zener diode now. The schematic has all these test points, but no voltages, like pioneer schematics. Do you really need to probe the transistor legs?
painttoad said:
technics used alot of mitsubishi capacitors and these are well past their prime. just this morning i fixed a sa5550 with a dead channel, a 100uf cap in the tone control circuit had turned into a .22ohm resistor. replaced it and problem solved.

since it's 2 dead channels, start at the power supply and verify voltages.

service manual is here:


https://www.audioservicemanuals.com/t/technics/technics-sa/149543-technics-sa-5760-service-manual
Click to expand...
, pai
 
upload_2023-5-29_14-21-40.png

The schematic from HFE has transistor voltages posted..
 
Jludowise said:
Thanks, painttoad. This unit was recapped (minus the tuner board) by the previous owner, who owned an audio repair business. I'm wondering if it's a zener diode now. The schematic has all these test points, but no voltages, like pioneer schematics. Do you really need to probe the transistor legs?

, pai
Click to expand...
and if you are referring to the letters in solid circles, they are not test points, they are just showing connection points to other circuits or other points in circuit
 
avionic said:
Forgot your password...:D
Click to expand...
:biggrin:
nope. they even allowed me to make another account and then killed it. new registrations have been closed since then. i occasionally check but i found that i don't need hfe. i can find schematics elsewhere.
 
Update... still going through the transistors, but found some unusually low voltages on the collectors of TR509 and TR510 (-21.2 ish V vs. 1.4)
 
It seems unlikely that there are faults in L and R channels that are resulting in identical out-of-spec bias voltages. I'd look to circuitry that's COMMON to both L and R channels for root cause.

Curious - did the unit work AFTER being re-capped by the PO?

Do you hear ANY sound? (i.e. small clicks or pops as the controls are moved, or hiss at max volume?) Have youinvestigated the TAPE in and OUTs? (they're useful 'mid-chain' injection or measurement ports to get a clue whether the issue is up or downstream)
 
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