Pioneer sx 1010 voltage problem

K

kenneth501

New Member
I'm new to this but on a steep learning curve. My sx1010 was dead but after looking at the many posts I have replaced all caps and transistors on the power supply board, and both power amp boards. It now fires up and the protection works as it should. The left channel seems to be ok but the right channel crackles and is not as it should be. I can increase the volume with no cut outs.
When I measure the output on the power amp boards I am getting 12.5v on pin 13 which should be -0.6 on the right channel. Pin 10 is correct.
The left channel board reads as it should, the discrepancy is in the right board.
Have checked resistors R25,26,27, and 28 and all read correctly.
Have attached schematic as I am sure it may be something simple that with my inexperience I have missed.
 

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The Drivers Q8 and Q9 are suspect. For now, do a good visual check of Q8 and 9. The outputs 2SA747's are running at a high output. Not good.
Only run on the DBT until other wise.

How did the Amp adjustments go? DC neutral and the Idle settings?

Others will lend some advice as well.
 
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Also Doublecheck the pin orientation of ALL the transistors you replaced. Use the datasheets for each. The pin layouts on the NEW transistors are NOT what they are on a lot of the old transistors. SO you might have installed one or more incorrectly.

What did you replace each transistor with and from where, on the amps? Did you replace Q1-2-3(2sa726), and Q4,5 (2sc1451)? These MUST be replaced pre-emptively. The 1451's are especially suspect.

Larry
 
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Did not do any amp adjustments while things looked wrong.
Will check transistors again.
Q1-2-3(2sa726) were replaced with 512-KSA992FBU Q4,5 2sc1451 were replaced with 512-KSC3503DSTU all from mouser.
 
Have found that I have put Q8 in the wrong way round. Have now put this right but right channel still crackling and distorted. Checked the pin voltage on the amp boards and now the pin 13, which was showing 12.5v now shows 0.4, but according to the left channel board that works, it should be -0.4 not positive.
 
Do you have and are using a DBT?

Did not do any amp adjustments while things looked wrong.
Click to expand...
Can you still set the offset or idles with the PNP's outputs running at full speed? No

Do you know about the Bias and Idle adjustments for the amp? This is not a step that can be forgotten. If so, what were the finial settings?
Please answer! :nono: You shouldn't mess with it, until you provide more info.

The outputs 2SA747's are running at a high output. Not good.
Click to expand...

There maybe damage to these right channel PNP outputs transistors.

Slap me if I'm wrong!!! :yes:
 
There are important initial settings for the replaced trim pots.

And the reversed transistor may have either been damaged, or damaged others.

Look for ANY transistor without about 0.6v between emitter(black dmm probe) and base (red dmm probe). NPN transistor will be about +0.6v, PNP transistor will be about -0.6v

Otherwise pull each and 6 way test it on the duff channel.
 
I do not have a DBT and with my lack of experience not sure what it is. I can hear you laughing now.....

I have the service manual which describes how to set the amp boards with an 8ohm dummy load. I do not have the dummy load, is it possible to adjust this with a pair of speakers connected, I doubt so, but until I get the board correct I will cross this bridge as I come to it.

I have not replaced the trim pots so they have not been touched since rebuild.

I have checked the base outputs of all the transistors on the board as MF suggested and found Q6, Q11 and Q12 to be 0 which I would expect them now to be faulty.

Before I order more parts advice would be much appreciated. Thanks in anticipation
 
kenneth501 said:
I do not have a DBT and with my lack of experience not sure what it is. I can hear you laughing now.....

I have the service manual which describes how to set the amp boards with an 8ohm dummy load. I do not have the dummy load, is it possible to adjust this with a pair of speakers connected, I doubt so, but until I get the board correct I will cross this bridge as I come to it.
Click to expand...

The DBT (dim bulb tester) is a way to power up a unit after work has been done to it, to ensure a safe test load upon start-up. Easy to build: Compact Dim Bulb Tester

Regarding the dummy load, I too, just went through a multiple board rebuild (SX-850) and was curious about the dummy load described in the service manual. Searching AK I found a quote from markthefixer: "Zero volume (no sound) on the volume control is quite adequate, neither 5.1k resistors nor 8 ohm speaker load resistors are needed. They were slavishly following something that had little basis in reality."

That was found in this thread: SA9500 bias DC offset question

So, speaker button off, zero volume is what I did. I was able to dial in the trim pots exactly where they needed to be!
 
We do not laugh, we were all at your point of experience at one time. There is NO SUCH THING AS A DUMB QUESTION, dumb is blindly charging ahead.

Please, on those "bad" transistors, POST what you read, perfect 0.000 's are unlikely, and when less than 0.6 is found, include e,b,c ground referenced (black dmm lead to a bare metal chassis ground, probe with the red lead) voltage readings.

Then pull the transistors and do the 6 way diode test on each and post the results.

we assume NOTHING, we investigate until we KNOW.

BTW, Q11 and Q12 are the power limiters, and are an exception to the 0.6v rule, they should be well under 0.6v because there is no power to be limited with no speaker loads. :D

Sometimes I include or leave "checks" in the instructions to have confidence in the rest of the readings.
 
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kenneth501 said:
Have found that I have put Q8 in the wrong way round. Have now put this right but right channel still crackling and distorted. Checked the pin voltage on the amp boards and now the pin 13, which was showing 12.5v now shows 0.4, but according to the left channel board that works, it should be -0.4 not positive.
Click to expand...

EDIT 16AUG2014. DISREGARD THE 1st PARAGRAPH. I got confused as to what you were saying left to right. See post 17.

The voltages are correct! You have a split voltage power supply that put's out POSITIVE + and NEGATIVE - voltages. So one side is Positive and the other side is Negative. Don't rely completely on the board voltages for comparisons especially for voltage polarity. Use the schematic too. You'll see what I'm talking about, in this case look at the emitter voltages for Q9 and Q10.
DISREGARD ABOVE END EDIT

Q9 should be showing +0.6v (or so), and Q10 should be -0.6V (or so). There will be variances in voltages, due to component differences and wall voltages so 10% either way should be ok.

Larry
 
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larryderouin said:
The voltages are correct! You have a split voltage power supply that put's out POSITIVE + and NEGATIVE - voltages. So one side is Positive and the other side is Negative. Don't rely completely on the board voltages for comparisons especially for voltage polarity. Use the schematic too. You'll see what I'm talking about, in this case look at the emitter voltages for Q9 and Q10.

Q9 should be showing +0.6v (or so), and Q10 should be -0.6V (or so). There will be variances in voltages, due to component differences and wall voltages so 10% either way should be ok.

Larry
Click to expand...

aren't both amp boards the same layout then ?
 
Yep. One 1/2 of each board run on Negative and the other 1/2 runs on Positive. What he's saying is Q9 was showing a + voltage while Q10 was showing a negative voltage and the way he understood it Q9 should have been negative also. Two identical boards.

attachment.php
 

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i was going off this "Checked the pin voltage on the amp boards and now the pin 13, which was showing 12.5v now shows 0.4, but according to the left channel board that works, it should be -0.4 not positive."
pin 13 should be negative on both boards shouldn't it ?
 
Yeah. Both pins 13 are negative. I think where I got cornfused is the way he wrote it, I was thinking he was comparing the positive side of the board (same board pin 15) against the negative side(pin 13). I edited my original post.
 
Really at a loss with this. Since I changed Q8 I have also found Q12 to be not as it should. I have now replaced Q12 and when I switch on the protection kicks in and out and stays out.
I have checked all the transistors for correct positioning and checked them in circuit with the dmm. Any I found with faulty reading I released from the board and checked and they were ok. I have checked all the resistors and again released any which read wrongly. I have checked the base to emitter on all transistors and they read 0.5 to 0.6. I checked the left hand channel board transmitters which were working correctly comparing them like for like and they seemed ok.
As the protection now will not kick in I am considering replacing all of the transistors in the right faulty board again with new as there must be damage to have the faults continuing.
 
Are you using the DBT after making any changes with components? You will need to perform the DC Balance and Idle adjustments. This may be why the protection goes in and out.

You don't seem to be listening to any advice. You are only telling us information after the fact. Now I am worried.

Stop!
Please list what you have done so far. I hope the DBT is included in the synopsis.
 
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AGREE WITH ZEB. STOP NOW and LIST BY BOARD and Position EACH and EVERY TRANSISTOR you've replaced and with what.
 
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