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Technics SA-303 Help

OldZofTorC

OldZofTorC

AK Subscriber
Subscriber
I have really believed i would figure this out but it is just kicking my ass. IC603 is aSTK1039. I have moved the two STK around and the Right channel will work with either one. I must have F601 removed to enable me to play the right channel. With the fuse in place i get noise and the Dim bulb lights up. I have undone the ribbon cable represented as 24-23-22-21-25 in circles. having done this I can leave F601 in place. Voltage measurements with this situation is (w/dim bulb) at IC603 pin 1 neg 32v, pin2 neg 34v, pin 4 pos 29v, pin 7 pos 29v, pin 9 pos 31v, pin 0 pos 30 V. I have pulled and checked c621-623-625-627.R617-619. I have taken measurements with the ICs out of circuit. Only difference between the two is .5v at 4 and 7 on the bad channel vs. .026v on the good chip. So as far as I have gotten is that it is Positive voltage that is getting into inputs. I have been on this for days and would normally have at least stumbled on to the solution.
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OldZofTorC said:
I must have F601 removed to enable me to play the right channel. With the fuse in place i get noise and the Dim bulb lights up.
Click to expand...


Shorted out headphone jack or speaker select switch.. Ohm out the headphone jack and the speaker select switch.Also have a good look at the speaker binding posts for a stray bit of wire shorting out the binding post for the right channel.
 
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Thank you for the response.I am not expecting you to try to figure this out for me. I am so deep into it I am bound to be close. I just lack experience. I have lifted the cable before the jack and selector switch. The problem is at the input. I dug in deep last night removing components. I am concentrating on the input at pin 0 which is at 32V (dim bulb). Also at the ribbon cable leaving the IC pin 24 has the same voltage. With the ICs out of circuit there is a difference at the ribbon cable .5v on the bad channel, .025v on the good channel.
 
OldZofTorC said:
Thank you for the response.I am not expecting you to try to figure this out for me. I am so deep into it I am bound to be close. I just lack experience. I have lifted the cable before the jack and selector switch. The problem is at the input. I dug in deep last night removing components. I am concentrating on the input at pin 0 which is at 32V (dim bulb). Also at the ribbon cable leaving the IC pin 24 has the same voltage. With the ICs out of circuit there is a difference at the ribbon cable .5v on the bad channel, .025v on the good channel.
Click to expand...
:lurk:
 
The voltages at the differential amps AN7060 are good. The voltages at Q601 are all around 32V. Feeding that 32V into the STK and causing my troubles. I replaced Q601. Man I want to get this off my bench.
 
I use a desktop also, don't have a 'smartphone'.

Let us start with basics.
IC603 is removed at this time?
On DBT, what watt bulb?
Measure dcv at IC603:
Pin 9:
Pin 2:
Pin 0:
Pin 1:
Pin 7:

Measure dcv at IC601:
Pin 8:
Pin 9:
Pin 5:
Pin 4:
Pin 1:
Pin 2:
Pin 6:
 
100w dim bulb. 603 is out of the circuit. Ribbon cable to headphone jack is lifted. 680ohm resistors are in between 0-7 and 1-4.
Pin 1 19.3
Pin2 34. 5
Pin 7 25.8
Pin 9 12mv
Pin 0 32.5
IC 601
Pin 8 33V
Pin 9 33V
Pin 5 -6.9V
Pin 4 0V
Pin 1 -79mv
Pin 2 -80mv
Pin 6 31.9V

All leads on Q601 are 32V
 
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These are IC603 pin number dc voltages?
Pin 1 19.3
Pin2 34. 5 Pin 2 is the negative supply voltage pin, should be -40.2vdc, lower on dbt
Pin 7 25.8
Pin 9 12mv Pin 9 is the positive supply voltage pin, it should be +40.2vdc, lower on dbt.
Pin 0 32.5

Is your meter black lead connected to chassis ground, and measuring with red? (I am presuming it is a DMM)
 
Well, that makes more sense now, pins 4 and 7 are halfway between 0 and 1, as i was looking for. The power supply rails are symmetrical (enough) to be comfortable with while on dbt.

Please post dcv:
For Q601:
E:
B:
C:
E to B on mV scale:

For Q603:
E:
B:
C:

Negative side of C627:
 
Q601 has 32V on all legs.
Q603 E 33 C 34.2 B 33.7 E-B .723

C627 -6V and 26v on the positive side.
 
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Please put one probe on the emitter of Q601 and the other probe on the base of Q601, not a ground reference voltage, a measurement directly from the legs/pads voltage. I am hoping for a pn junction voltage around 0.600 vdc, but post whatever it actually is.
 
OldZofTorC said:
I'll be back. I have to go take care of a job before it gets too hot out.
Click to expand...
No problem, your project, your schedule, :)
It looks like B-E of Q603 is what you reported as 0.723.
Please put one probe on the emitter of Q601 and the other probe on the base of Q601, measure dcv:
 
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