Technics SA-160, power transformer output too high

[JayPare]

I'm in the process of bringing back to life a SA-160 only to help me improve my electronic skills. I think I'm pretty close to get it back to life (link to the main thread), but I'm worried about voltage too high from the power source circuit:



Indeed, I'm getting -43 and +43V instead of -35.5 and +34.7V. Maybe this is the reason why some other prts got burned?

Also, I never found this speaker impedence switch neither that D781 diode on my actual circuit. My guess is I don't have the same revision of the circuit compared to the schematics I found online.

A lot of part have been removed further in the circuit for testing so I wonder if those voltage might be off because of this or I should be worried about not getting the correct values (-35.5 and +34.7V).

Any help will be appreciated and I want to remember this receiver will be on sale when serviced and I will give all the profit to Audiokarma since I benefited from help from a lot of people here.

 

[mbz]

Does the unit have a voltage selector, typically on rear panel. Also does the voltage specified on rear panel match
your mains voltage, perhaps you have a 100VAC unit?

Does the transformer look original? Part number correct?

Spkr impedance switch selects different secondary windings, did you try switch in both positions?
Will crunch some numbers...

 

[JayPare]

Spkr impedance switch selects different secondary windings, did you try switch in both positions?

I don't see any switch for the speaker impedance unfortunately. Also, I'm pretty sure I have a 100VAC unit but I will double check this and the rest tonight! Thank you very much!

 

[mbz]

Also, I'm pretty sure I have a 100VAC unit

What is the mains voltage in Canada? 120VAC?

I don't see any switch for the speaker impedance

Expect it on the rear panel though could be a schematic error/update.
Switch shows either 20.7VAC(~29VDC) or 28.5VAC(~39.5VDC). The schematic guiding voltage (34.7VDC) is about
halfway between these 2 voltages.

Possibly the 4 ohm option has been removed in late production due to amp meltdown, now the amp is hard wired to 8ohms
so expect about 40VDC at main filters.

 

[century tek]

Not sure how a factory transformer or power supply can make higher voltage than what it is designed aside from a higher mains input or a shorted winding (rare), but I think you might be looking in the wrong place. What is wrong with the unit to begin with? Pics?

 

[mbz]

Think this is an intrepretation issue of the guiding voltage. Expect about 40Vdc with some drift due to mains drift.

 

[JayPare]

Here are the answers!

Does the unit have a voltage selector, typically on rear panel.

No.

Also does the voltage specified on rear panel match your mains voltage, perhaps you have a 100VAC unit?

It does match the voltage. This is 120VAC.

Does the transformer look original? Part number correct?

It does look original and by Googling the part number, it a Panasonic (Technics) transformer.

What is the mains voltage in Canada? 120VAC?

Yes. Sorry about saying 100VAC, I misread 120VAC.

Expect it on the rear panel though could be a schematic error/update.
Switch shows either 20.7VAC(~29VDC) or 28.5VAC(~39.5VDC). The schematic guiding voltage (34.7VDC) is about
halfway between these 2 voltages.

Possibly the 4 ohm option has been removed in late production due to amp meltdown, now the amp is hard wired to 8ohms
so expect about 40VDC at main filters.

Yeah I really think this option have been removed. When you say main filters, it's those big ass caps right?

Not sure how a factory transformer or power supply can make higher voltage than what it is designed aside from a higher mains input or a shorted winding (rare), but I think you might be looking in the wrong place. What is wrong with the unit to begin with? Pics?

You can go to the main thread for the main problem. Basically, it wasn't powering on at all!

Think this is an intrepretation issue of the guiding voltage. Expect about 40Vdc with some drift due to mains drift.

So those +/-43Vdc looks fine for you?

 

[mbz]

So those +/-43Vdc looks fine for you?

Yep, I'd focus on those transistors etc in the regulated supply.

 

[Lavane]

Yep, I'd focus on those transistors etc in the regulated supply.

I agree, check the voltage regulator and any other transistors in the power supply. Also check any resistors, starting with anything larger than 1/2 watt. Checkng the values by lifting one leg from the circuit board. I have run across dropping resistors that have driffed. It doesn't happen often, but it can happen.