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Yamaha PX-3 photointerrupters and other issues causing problems

TR 7 on the E side gives 11.94 volts, on the B side it has 11.82 volts. Does that mean it is good?
Resistor R35 gives 11.52 kOhms
So, pin 11 is not getting voltage but TR 7 is, and it would appear that the resistor is OK as well......hmmmm.....why is IC 2 pin 11 not getting voltage???
 
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It is the 3rd lead of the transistor. I can't tell from the copy of the board layout that I have?
 
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Wait... something doesn't look right??? If I look at the symbol and follow the lines I get this.
But... from the schematic...
C is connected to R35​
B is connected to R32​
E is connected to R31, R33, R38​
Did you replace this transistor in your recap of the board?
Maybe the board layout is incorrect. Can you read the part number of the transistor that is in the board?

1742709870500.png
If the package looks like this, then the board layout shows the transistor with B & C leads swapped (according to the schematic).
1742711062933.png

EDIT: I think it should be drawn like this to match the schematic.
1742713247545.png
 
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No, I did not touch that transistor and can verify that it came directly from the factory this way and worked perfectly for many years.

Hang on.....I may have to take the board off the plinth again because I can only see the side with the traces.

Part # A999 12E

And yes, there seems to be a discrepancy with the schematic because the pins do not follow. I have E on one side, C in the middle, and B on the other side where C appears to be connected to the R35 resistor.
 
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That's good... ECB leads.
Only a couple of things to check, with power off measure the resistance across R35. It should be around 12K ohms. Just to make sure it is not shorted.
 
Robert Lobo said:
@Fishead please check the switch whether it is making contact. I mean if it is not then I think it remains open and the voltage in pin 11 will be high. Kindly check for oxidation of the switch contact points or just clean it with proper contact cleaner solution or just sand the points with a fine grid sand paper. This is a critical point which sets the automatic logic. I mean if the pin 11 is high then no function will be operative (the logic will be considered as the tonearm is on the record and in play position) if the pin 11 becomes low then the logic would consider it to be off record or in raised position, so cueing, etc function operate.

So, if the contact of the switch is not closed properly, then the pin 11 would be high and no function will operate. You need to ensure the switch remains in normally closed position when the tonearm is in lift/up position.
Click to expand...
I think I made some confusion on pin 11. Please read pin 11 high and low feed as low and high. I.e when the pin 11 is low the tonearm playing record and when it is high it is off record or raised position.

Your reading on pin 11 should be 11.6v (high) in the tonearm raised position, however you are getting reading of 0v (low) instead. This would indicate the logic control that the tonearm is playing record and other functions will not work.

Hope I have removed the confusion.
 
dankik said:
That's good... ECB leads.
Only a couple of things to check, with power off measure the resistance across R35. It should be around 12K ohms. Just to make sure it is not shorted.
Click to expand...
Power off, resistance across R35 is 11.14 kOhms
 
Robert Lobo said:
I think I made some confusion on pin 11. Please read pin 11 high and low feed as low and high. I.e when the pin 11 is low the tonearm playing record and when it is high it is off record or raised position.

Your reading on pin 11 should be 11.6v (high) in the tonearm raised position, however you are getting reading of 0v (low) instead. This would indicate the logic control that the tonearm is playing record and other functions will not work.

Hope I have removed the confusion.
Click to expand...
Yes, it reads 0 volts no matter if the tone arm is up or down and that seems to be what we are chasing down at the moment. Why does pin 11 get no voltage???
 
Hey guys, my eyes are getting really tired so I'm going to call it a night. Let's please resume tomorrow should you have time. Thank you for staying with me, I think we will find the solution!
 
Fishead said:
Why does pin 11 get no voltage???
Click to expand...
OK, so R35 is not shorting the signal, TR7 collector to Gnd. So, unless you have a solder bridge along the trace from TR7 emitter to IC2 pin 11 (shorting it to ground), I think that your transistor TR7 is bad. Carefully examine the trace.

You can also check continuity with power off from Gnd to IC2 pin 11 to check for a short.

Now, if TR7 is bad you probably cannot get a direct replacement. There is another AK thread that talks about alternative parts.
https://audiokarma.org/forums/index.php?threads/2sa999-transistor-substitute.670035/

@Robert Lobo, it sounds like TR7 base and emitter voltages are good, but the transistor is not driving the collector to 11v. There is no short on R35 to ground so unless there is a short on the trace elsewhere, I think the transistor is bad. Ideas?
 
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Good morning all, and @dankik I will check continuity from pin 11 to ground with power off. I have not done anything that could have damaged that trace but I will look very carefully.
 
OK, so with the power off, I get continuity to ground, not only on pin 11 but on EVERY pin on IC 2. What am I doing wrong?
 
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