My 7070 Suddenly has no sound

Tr04 on F-2625 is testing bad! But I need to find a replacement before we know for sure.

2sc945(K)
printed on tr is
"c945
ak65"
 
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KSC945C - make sure you get the "C" designation which is center collector. I imagine the one in it is ECB.
 
Update, With the help of the mighty and brilliant Robisme, I have traced the loss of audio signal to F-2620(the equalizer and mic circuit board). So the search begins for broken components there. The audio signal trail ended approx, at R55 on F-2620.
 
If you are using AUX input, that wont be the problem. Phono, perhaps.

Check the input and output of F-2621. Make sure the Dolby adapter button is not pressed.

Edit: OK, so it looks like the signal does come back through F-2620.

Dolby board F2621 15, 16 output. > EQ F2620 18,19 input - 24,26 output. > Tone board F2622 4,2 input - 5,6 output.
> filter board F2623 1,2 input - 3,4 output. > Driver F2624 1,4 input (10,11),(22,23) output.

Check voltages on F2626 pin 2 41v, pin 3 41v, pin 4 39v.

Sorry, I am at work looking at a tiny schematic.

Rob
 
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Found another bad transistor on the power supply board TR02 a PNP that has a pinout ECB. Printed B560 D-5F. All leads are reading over limit.
 
Nothing new to report, just waiting on parts... Sigh. Picked up a new digital multi meter that reads capacitance, some new soldering tips and instead of tearing apart my shop looking for my helping hands soldering station any more, I bought one on Amazon.
 
Today I recapped the main power board, all except the bipolar 80v 4.7 uF, because they are nonexistent these days. I also swapped out two transistors tr02, and tr04. Tomorrow, I will continue capping the driver board and the protection board. I should have more information for you all tomorrow. :)
 
I will pick some of those up Rob.

I also witnessed the lights flickering today so I will have to fix the solder flow on the illumination board.

I spent the morning following around voltages on the circuit board and everything seems to be healthy on the power board. I ran out of time so recapping the driver board and protection board is going to have to wait until tomorrow. It is coming back to life! I was reading some troubling voltages from Tr01 on the main power board, which had tested fine earlier, reflowed the solder and it is working fine.

I also checked the output transistors today for shorts and continuity and everything checks out. With the recapping, and bias adjustments we should have sound tomorrow!
 
Ok no big deal or anything, but I had some extra time to recap. We now have voltage moving through the audio outputs. I have yet to bias adjust, but so far it seems that old caps blew, blew 2 transistors on the main power board, and a diode near the relay. I haven't checked the transistors on the driver board yet, but that will be tomorrow.
 
It definitely is! It was a good day. What I have learned, always go for the recap, and be diligent with your solder flows. I'm kind of sad, once this project is over I will need to find another broken receiver to restore.
 
Phystudent (Rob)

Don't worry about running out of stuff to tinker with. I have an SX780 that lost one channel, 2 Sansui 2000's that sound great but being late 60's units I'm sure they could use some love. I also have an AU-717 that goes into protection mode if cranked to loud and a SA7500 II that might need to be freshened up at some point.

Looking forward to getting the 7070 playing in the shop again.
We'll both enjoy it when I have you and your family over for a cookout.

Ciao
Steve
 
We have sound back!

F-2626
green 12.5 V
yellow 38.9 V
red 38.8 V
orange 36.4 V

F-2624 recapped, fuse resistors replaced
Putting out great sound

while trying to bias the current the dc current seems to be fluctuating. It could be my multimeter. Should the milliamps set to 30 milliamps and stay there or is it normal to view some fluctuation when adjusting.
 
Well Phystudent My 7070 sounds GREAT! It seems like after the first week it got even better????

Thanks again.


BTW I have yet to try out the Pioneer SX780 that you brought back to life.
 
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