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Technics SA-303 Help

That is fine, don't reinstall anything.
I want to try it on full power, if you are willing, then retake some measurements:
Do dcv comparisons between Left and Right channels:

Feeds both channels, Q603:
E:
B:
C:

IC603 pin 9:
IC603 pin 2:
IC604 pin 9:
IC604 pin 2:


IC601 diff amp pins
1:
2:
3:
4:
5:
6:
7:
8:
9:
Q601:
E:
B:
C:
- on C609:
+ of C627:
- of C627

IC602 diff amp pins
1:
2:
3:
4:
5:
6:
7:
8:
9:
Q602:
E:
B:
C:
- on C610:
+ C628:
- C628:
 
Feeds both channels, Q603:
E: 37.75
B: 38.56
C: 39.0

IC603 pin 9: 39.3
IC603 pin 2: -39.4
IC604 pin 9: 39.3
IC604 pin 2: -39.4


IC601 diff amp pins
1: -72mv
2: -75.6mv
3: /
4: 0
5: -6.3
6: 39.76
7: 36.05
8: 38
9: 37.8
Q601:
E: 37.4
B: 36.6
C: 37.3
- on C609: -42.6mv
+ of C627: 29.76
- of C627 -6.61

IC602 diff amp pins
1: -70.3mv
2: -68mv
3: /
4: 0
5: -6.3
6: 37.22
7: 38.6
8: 38.0
9: 37.8
Q602:
E: 37.7
B: 37.1
C: 1.0
- on C610: -32mv
+ C628: 10mv
- C628: -18.4v
 
I'll be looking at C627 while I wait.
R619 2.7k -36 drops to -6.6v
R618 2.7k -36 drops to -18v.
 
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I been in my shop all afternoon, working on my SX-1050, and listening to Linda Ronstadt, thank you for the Avatar! Just got back in the house.
I forgot to ask for the output pins dcv on the STKs, 4 and 7

Measure dcv across R611, should be 0v.
 
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I wish I was working on a 1050.
LInda has always been my crush. Check out TRIO, Ronstadt-Harris-Parton.
R611 is 0v
4 and 7 is at 30V
 
I remember hearing her singing on the radio back then, but I did not have a music collection, and did not know who it was. I didn't have a stereo either. Now I do both and am adding a bunch of hers to my collection. I am also a long time big fan of Emmy Lou Harris. I have listened to some of Trio the last few days also.
 
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Check the orientation of Q601 by following the traces to see where they are connected, make sure the transistor collector is going to IC603 pin 0, base is connected to IC601 pin 6, and emitter connects to R615. Maybe the silkscreen is wrong? Verify R615 is 33Ω, orange orange black.

Everything I am seeing points to that transistor. The polarity of the inputs of IC601 are reversed from that of IC602, telling me the diff amp should be trying to resolve the issue, but the transistor is not doing what it should. The next thing I would do if Q601 is oriented correctly is test every trace from every component in that area for continuity. That will be tedious.
 
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I will do that. I have been chasing out these circuits and I am becoming able to see how everything is interconnected. I see how you have come to your conclusion. I will let you know what I find.
On a similar note. The music of that time was all interconnected. You will hear Linda and Emmy Lou on so many of the records of the day. That brought me to spend a whole day on Gram Parsons last week.
 
Well Sir so many thanks. Thank you for staying with me. I had given up, you kept me on track. The confidence of understanding is what I needed, I had lost that here. And of course I am kicking myself in the ass because the problem was so obvious once I finally gave it the correct observation. So the fix was a correction to a burnt trace between C627 and C615. I am so relieved to be rid of this thing, and even more relieved to not have to given up and call this a loss. I can keep my win/loss at 0 in the loss category. I do not have even a good understanding of feedback circuits but I have much more than I did a month ago when I started on this piece. Thank you again.
 
Whew, what a relief that is. You are most welcome. A break in the negative feedback path caused it all along. I bet somebody back in the chain of possession shorted it out somehow, could not fix it easy, and dumped it. So far I am at a no fail repair rate also, the only ones I have not seen repaired were one the OP gave up on. Thanks for sticking with it! And thanks again for the Avatar, that has added good sounds to my music collection :bigok:
Enjoy the Tunes :jump:

P.S. FWIW, that is my second Technics repair, I usually hang out in the Pioneer forum, but every so often I drop into Solid State to look for an interesting power supply or power amp problem. The tough ones are so satisfying!!
 
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I do most of my work on Pioneer also. I personally have an 850 a 1050 and a 1250. I did a full rebuild on an SA 9800 and now I would like to have one of those. Btw have you had any luck with a dim floro-display?
and are you familiar with Allison Krauss?
 
OldZofTorC said:
I do most of my work on Pioneer also. I personally have an 850 a 1050 and a 1250. I did a full rebuild on an SA 9800 and now I would like to have one of those. Btw have you had any luck with a dim floro-display?
and are you familiar with Allison Krauss?
Click to expand...
Never touched a unit with a dim floro display. What I have seen on AK is an overvoltage on the ?cathode? lead can knock a build up off the wire that it acquires as it ages, or increasing the voltage . . . :dunno:

I am doing a refurb on my SX-1050 I bought new in ''77 (I think). I had an SX-780 for years that died. I fixed it up with the hbrown/rcs16 custom STK replacements after cleaning it up and gave it to my son for a wedding present. I have another SX-780 in the queue that need some major electronics love and cabinet work (not my favorite part). I also have an A-88x that needs some serious deoxit work. It played great when it worked, but the controls are crap for dropouts, so bad it is unusable. That one might get put on the market after a refurb, but it will be a while (i'm not a flipper). It was cheap from the 'bay some years back.
Will check out Allison Krauss.
 
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