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Pioneer SX-950 Restoration Project

markthefixer said:
I have a problem with your entries,, you use a dash as a separator, but there are also negative voltages to be recorded. I assume dash space is a separator while dash number is a negative voltage.

2 & 3 are the function lamps, and if they have been changed from the 50mA incandescent lamps there will be a difference.
otherwise pins 27 & 28 feed ac to D9 & D10 through FU4 & FU5 to C12 1000uf / 35v

Since the 13.5v at pins 4 & 5 is ok, I suspect a problem with R20. R21, R22, Q9, Q10, C14 & or C13. See how stable the base voltage of Q10 is.

It should be mumble mumble {13.24 + 0.6 = 13.8 13.8 x (R22/(R21 + R22))) = 6.325 6.325 - 0.6 - 0.6 = 5.125 } 5.125 at pins 2 & 3 / base voltage of 6.325 .

Offset will be different, the power supply voltages changed.
Click to expand...
Attached are the numbers I got as per your comments and my subsequent investigation. Base VDC of Q10 was rock steady - I verified all the resistors and caps as good (caps I pulled to measure - they were all new so no surprise they were spot on). Some of the numbers on Q9, Q10 make no sense to me as you can see - is it possible that the LED lights throw the circuit for a loop and therefore may not conform to the expected VDC at pins 2/3? Lights do burn good on the unit. Now the good news - it works as per (Lucky? because I sure don't know what I did to get it to work as good as it does now):music: :
 

Attachments

  • response.jpg
    response.jpg
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Yes, with LEDS the voltages will change somewhat. Depending.

I need these voltages, measured and posted. Q9 & Q10 have problems. Q8 is a needed baseline.
Q8 emitter should be 0.6v less than Q8 base.
Q10 emitter should be 0.6v less than Q10 base
Q9 emitter should be 0.6v less than Q9 base (and Q9 emitter should be 1.2v less than Q10 base)

I really shouldn't be saying "should be" for the voltages, so as to NOT influence you towards a reading.

upload_2021-8-17_0-7-27.png
 
markthefixer said:
Yes, with LEDS the voltages will change somewhat. Depending.

I need these voltages, measured and posted. Q9 & Q10 have problems. Q8 is a needed baseline.
Q8 emitter should be 0.6v less than Q8 base.
Q10 emitter should be 0.6v less than Q10 base
Q9 emitter should be 0.6v less than Q9 base (and Q9 emitter should be 1.2v less than Q10 base)

I really shouldn't be saying "should be" for the voltages, so as to NOT influence you towards a reading.

View attachment 2317086
Click to expand...
I believe all the requested voltages are posted in the thumbnail image link two posts above (attachment called response.jpg) - the image needs to be expanded to read the voltages which were all measured at the transistor BCE terminals. I agree they appear to be out of whack from what it should beso now thinking I should pull Q9 and Q10 from the board and measure the trannys on my Peak DCA55 tester. CAPS and resistors all measure perfectly good so thinking it can only be the the transistors but even that is not making sense to me...
I know I can't leave it as is but the receiver is sounding darn good now:confused:
 
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rcs16 said:
Q10 is your problem
Click to expand...
Thank you rcs16. Believe that is supposed to be a KSC2383YTA. Pretty sure I have an extra one on hand. Got a busy work day on the base today but will try to pull it and swap it out this evening. Entirely possible I got the leads in wrong when it was swapped out. I guess the only reason the lights are working is it is still providing power under the 8V rating of the LEDs and old incandescent at pins 2 and 3 by sheer chance...:eek:
 
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Timothy Flath said:
I believe all the requested voltages are posted in the thumbnail image link two posts above (attachment called response.jpg) - the image needs to be expanded to read the voltages which were all measured at the transistor BCE terminals. I agree they appear to be out of whack from what it should beso now thinking I should pull Q9 and Q10 from the board and measure the trannys on my Peak DCA55 tester. CAPS and resistors all measure perfectly good so thinking it can only be the the transistors but even that is not making sense to me...
I know I can't leave it as is but the receiver is sounding darn good now:confused:
Click to expand...

I wouldn't have asked, no less POINTED (WITH a picture no less), unless some were missing, or untrustworthy from a previous last go-round.

Although, subjecting Q9 & Q10 to the Peak DCA55 tester should also work toward sorting it out.
(as long as the passive components are behaving - which they would also have revealed)
 
markthefixer said:
I wouldn't have asked, no less POINTED (WITH a picture no less), unless some were missing, or untrustworthy from a previous last go-round.

Although, subjecting Q9 & Q10 to the Peak DCA55 tester should also work toward sorting it out.
(as long as the passive components are behaving - which they would also have revealed)
Click to expand...
Sorry those numbers were the latest go around I had, been at work and the unit is inaccessible so have been unable to poke and prod further with additional readings. Will do when I get it undressed again. Have had unexpected company staying with us so finding time and being a good host has been an effort. Hopefully I can find some time tonight...
Thought rcs16 comment that Q10 was bad was you (reading off a little bitty phone I miss context in some of these forums...:oops:
Cheers
Tim
 
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There is NO (repeat NO ) rush.

We will not loose interest, nor abandon the thread.

Thoroughly understood, deliberate, unhurried procedures are the objective.

In fact, the slower threads can be the best in terms of results - everybody has time to think and understand.
 
Q10 - checks out as good NPN on Peak - BCE all oriented correctly
hFE = 185
Test Ic=2.5 mA
VBE=.679V
Test IB = 4 275 mA
Leakage Current=0.0000 mA
 
Q8 shows good NPN oriented correctly on the PCB
HfE= 92
VBE=0.621V
Leakage = 0

Standby for requested numbers with board powered and amp segregated from preamp and speaker switches out....
 
Here is what I get now. After pulling and reinserting the three transistors the numbers seem to have fallen in line except the collectors on Q9 and Q 10

16292496627928370497262074687040.jpg
 
we don't extend much concern to the unregulated dc levels generated by fuses, diode bridges and just capacitors. That's what Q9 & Q10 collector voltages are.

If they were too low, then we might dig deeper. more like 20% low or worse. Regulated voltages within 10% are fine.
They even could be high - a multi voltage unit getting a "rich" feed.
 
Good you fixed the problem, cheers
The collector V for the 5.4V reg depends on the current drawn, it assumes incandescent lamps. With LEDs it is a lot less current so the voltage drop across the 100 ohm will be a lot less.
 
phono 1 and phono 2 are switched into the single (stereo) phono amp.

If the phono amp isn't working on BOTH channels, the first thing we look at is the power supply voltages, +28v (AWF-011 pin 6) and -19v (AWF-011 pin 2) .

There are two regulator circuits dedicated to delivering clean power SOLELY to the Phono (equalizer amp AWF-011) amp.
+28v is AWR-101 Q7, -19v is AWR-101 Q6.

The question becomes, what popped the power supply?

There are some transistors in the phono amp that go bad, and can hurt the power supply.

A handful of caps and transistors gets them literally better than new.
 
Akram said:
Tim and Mark thanks for the help. I worked on it this morning and both phono inputs are working. There is a hum which I can address at a later time but just the fact that the phono inputs are picking up the signal from the turntable has me excited.
Click to expand...
What type of turntable do you have? Some like my Thorens tables do not require grounding cables connected to the receivers. Most Do require this....
 
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