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Technics SA-303 Help

Since we are dealing with a dc error I would suspect a leaky or shorted cap, but not one that reads open.
Is the pot reading 4.6Ω or 4.6kΩ when centered?
 
Actually if you pull C605, C611 and R609 it will isolate the whole Tone Control section from the feedback path. I was looking for that option earlier, but just figured it out now. That leaves C609 to test.
 
1 18V
2 -34V
4 25V
9 34
0 32
This is with C609 tested and back in the circuit. C605, C611, and R609 out of circuit.
 
What is the dc voltage on the negative side of C609?
What is the dc voltage on the positive side of C627?
Measure as accurately as you can the dcv between pin 1 and 2 of IC601, and then the dcv on each with the black lead grounded.
Can you remove Z601 without damaging it? If so measure resistance across it.
 
OldZofTorC said:
C609 -285mv
C627 25V
IC601 1-2 165mv
1 -120mv
2 -285mv
Z601 in circuit -6V across.
Click to expand...
Pin 1 is very close to correct according to the schematic. Pin 2 is more negative than indicated.
One side of Z601 should be ground, the other side should be the same as IC601 pin 1. Where is -6v coming from?
With pin 2 being more negative than pin 1 the output of IC601 should be positive, which it is.
Measure DCV at each end of R605
Pull and measure resistance of R605.
 
I will do that. I should have a bit more time to spend on this today. I have this and another a problem on my vehicle that just won't let me win. I will be very happy when these are solved and I can move forward.
 
R605 reads 56k out of circuit. -290mv and -293mv in circuit.
Z601 reads as a resistor out of circuit 96K.
Yesterdays readings I mistaking provided were for D601 and not Z601.
I am going to put these back in circuit and reflow some joints near pin one IC 601
 
Now I have -30V on pins 1 and 0 on the STK.
Reading on good STK are correct as per manual.
I suspect you have readings you would like for me to take again.
 
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That is a good number for D601 as it is a 6v zener diode.
R601 still lifted? Should be . . .

Measure dcv on:
Q601:
E:
B:
C:

IC601:
Pin 6:
Pin 1:
Pin 2:

IC603 (STK):
Pin 9:
Pin 4:
Pin 7:
Pin 2:
 
R601 was in but I think I did that this morning. it is open now.
Q601 E 31.8
B 31.8
C 31.1

IC601 6 30.3
1 -121mv
2 -280 mv

IC603 0 32
9 34
4&7 25.3
2 -34
1 18.9 it appears 0&1 were 30v with R601 in circuit.
 
Q601 needs to be installed, as it is inside the feedback loop. One end of R601 lifted isolates the previous stages, to eliminate possible interaction.

OldZofTorC said:
with Q601,C619,C621,C6123 out of circuit.
I603
1 -30
2 -34
4 -30
9 34
0 -30
Click to expand...
That is what I would expect with Q601 removed.
 
OK, I probably need to look at the back of my eyelids for a while, then pick this up again in the morning. This one is perplexing, most interesting!
 
I sure appreciate your help.
I did my get vehicle straightened out yesterday. So as Seger says, Little Victory. I will be so relieved when this one is done, it has thoroughly owned me.
 
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