Technics SA-5070 service manual and troubleshooting help

[francisleo75]

Hi,
I'm trying to bring back to life a SA5070 Technics receiver, perhaps someone of you more experienced can put some lights on.

Firstly, I couldn't find a free service manual anywhere, so please if you have a pdf can you please share with me? there is nothing in the AK Database, I have no access to hifiengine.com and everything else is paid.
It turns on, lights ok, DC offset super high: 15.9V Left and 25V Right channel, so off course no output (Not plugged the speakers). the signal indicator is bouncing so I'm assuming the FM stage is OK, and that's it.

At first glance it seems a problem in the STK043 but, I'd like to check the power supply stage (again no manual for reference ;/) .NOTE: I ordered a Chinese IC but, after installed the resistors R631 and R633 started smokes...now I don't know if this IC came out bad or not. Basically, I'm lost. Any thoughts?
here is the readings on the IC STK043:
pin 1-16 with the manual values ( * ) -- > got a print shot from other thread with these values.
1. 120mv (-30mv)
2. -9.4V (-30mv)
3. -7.2V (0)
4. -24V (-23V)
5. -24.5V (-16.9V)
6. -25.3V (-25V)
7. -16V (0)
8. 23V (24V)
9. 25.3V (25)
10.-25.3 (0)
11. -25.3 (-25)
12. -24 (-16.9V)
13. -24.3V (-23.1V)
14. 5mv (0)
15. -9.4V (-0.03V)
16. 135mv (-0.03V)

 

[ecluser]

It looks like you have a short circuit between pins 10 and 11 of the STK043. Check that with your Ohm meter, at power off.

 

[francisleo75]

Thanks @ecluser
There is no short in there, I found the short in the 6 and 7 pins, confirmed with a multimeter out of the board.

However, still not working properly: I replaced the STK, and all caps part of power supply and amplifier board (excluding the 2 big power supply Caps 3300uf/35V that I have no spare available...see pic), Deoxit sprayed, fuses are good, checked the power supply (orange wires) 38V and 15V (bl & Yellow), tested the only 2 transistors on this board and both are good.

The reading looks like "better"... I can hear only a low audio response on both outputs with the vol. at the max or near max, dc offset on both channels are ~ 30mv.
Plugging the headphone, the sound it seems a little bit better (not sure) anyway, distorted and low...any thoughts?
Do you have a complete schematic to share? the only thing that I got from other thread is below...
Not sure what these gaps (bold) does mean :/

1. -30mv (-30mv)
2. -120mV (-30mv)
3. 0 (0)
4. -3.8 (-23V)
5. -3.2V (-16.9V)
6. -24.5V (-25V)
7. -0 (0)
8. 13V (24V)
9. 24.5V (25)
10.-0 (0)
11. -24.3 (-25)
12. -3.8 (-16.9V)
13. -4.5V (-23.1V)
14. 0 (0)
15. - 60mV (- 30mV)
16. -30mV (-30mV)

 

[ecluser]

Replace the 100 ohm resistors R621 and R631. On your picture they look burned.

 

[francisleo75]

Replace the 100 ohm resistors R621 and R631. On your picture they look burned.

Humm, good deal.

 

[gio4]

Hello!
Is a service manual for that device available?

A recently bought a used Technics SA5070

~50/60 Hz 170W
110V 120V 220V 240V

And I am looking for the service manual.