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Technics SA-5160 weak and distorted left channel

G

Gertjan90

Member
Hi guys,

So I promised a friend I'd take a look at her dads SA-5160, which she said had very weak FM reception, but before I can go after that, there is something more serious I need to adress:

The left channel sounds a lot quieter than the right one, and when I turn up the volume, it gets very distorted.
Through headphones, I can't get anything but a loud buzzing on the left side. Right channel plays fine.

First thing I did was swap the STKs, and they check out, problem persists on the left side.
If there wasn't any signal coming through and only a buzz (120Hz?) I'd suspect a transistor, but there is some distorted sound (at least through speakers) so I think a cap has gone bad.

I've gone in a little heavy handed and replaced all electrolytic caps in the left channel (that I could find) hoping I'd stumble upon the bad one, but no luck. No components look outwardly damaged, although I did replace R603 because it was discolored a bit. Still the same problem persists. All pots are thouroughly cleaned, btw.


I took some measurements, voltage in brackets are SM values:

STK left (IC601)
1: 0.34V (0.2V)
2: 0V (0V)
3: 5.2V (0.2V)
4: -18.6V (-28V)
5:-5.8V (-1.2V)
6: -28.8V (-29V)
7: 5.5V (0V)
8: 28.8V (29V)
9: 0V (1.2V)
10: 27.7V (28V)

STK right checks out fine.

TR501 (left)
B: 2.58V (2.6V)
E:1.99V (2V)
C: 9.55V (8.3V)


TR501 (right)
B: 2.64V (2.6V)
E:2.04V (2V)
C: 9.22V (8.3V)

I try to trace back to the fault, but my electronical knowledge is failing me.
If anyone can provide some input I'd appreciate it.
 
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You need to try to find the schematic for this - go to hifiengine.com - register and download the schematic or service manual if they are there.

Then you need to look for any small signal transistors that come before or after the STK in the signal chain. If it isnt dirty switch or relay contacts, I would look there
 
I've got the service manual at hand. No relay in this receiver.
The only small transistor before the STK is TR501, and I already replaced that when I was doing the caps. There is an IC for the tone control, but the voltages there check out, don't have them handy at the moment.
 
check the fusable resistor R603. Its a 100 ohm resistor. They can change value and open. Also check the fusables at R601, R607 (680 ohm) and R609 (470 ohm).


Pin 4 of the ic (channel left) is reading -18V instead of -28v. A bad IC, or a bad R603, or a leaky cap at C609 (220uf at 35V) are the only three things that can cause that. And you swapped the IC's and have the same symptom so IC is probably good.
Betting it is R603
 
Hi,
I already swapped out R603 and C609, but no change..
I've yet to check on the other fusables, but they look ok on the outside.
Next plan is to check ground connections.

This one has got me stumped.
 
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