Pioneer SX-525

Randy007

Randy007

Well-Known Member
having problems with a very distorted output...I thought it would be as easy as adjusting the bias but when I attempt to adjust the bias of the output, neither Pot adjusts at all....trying to adjust it to 30mV but no luck...any ideas thanks!
 
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What is the bias set to now?
Ajusting the bias trimmer VR2 set the voltages at Q8 and Q10 bases.
This in turn sets the voltages at Q12b and Q14b.

With amp powered off, you should diode check D2 and D4(resistance check)
also check the trimmer for continuity.

You could check if the VR has any effect of said voltages, monitor at D4 anode
and the VR, don't probe transistor legs.

What are the voltages at the output emitters pin 14, 16, expect less than 0.2Vdc
 
mbz said:
What is the bias set to now?
Ajusting the bias trimmer VR2 set the voltages at Q8 and Q10 bases.
This in turn sets the voltages at Q12b and Q14b.

With amp powered off, you should diode check D2 and D4(resistance check)
also check the trimmer for continuity.

You could check if the VR has any effect of said voltages, monitor at D4 anode
and the VR, don't probe transistor legs.

What are the voltages at the output emitters pin 14, 16, expect less than 0.2Vdc
Click to expand...
thanks for your response...this is a used amp I picked up at Habitat...output voltage on pin 14 is 39.3V, pin 16 39.3V, I checked the bias by connecting my meter neg lead to pin 10, positive lead to pin 14 reading was 28.5mV and I could not adjust voltage on VR2...on the other side I measured neg. pin 9, positive lead pin 13 reading was 15mV and again could get no adjustment out of VR1. Q10 base voltage is 39.2V and Q8 base voltage is 41V. these seem high to me, I'm thinking in the 20V range...what do you think?
 
also on the +50V I should have on pins 5 and 6 on the main amp board, I'm reading pin 5...21.9V and pin 6....46V
 
:lurk:
Check the Fuses (1.5A), the +50v supply also comes in on pin 17 through the Muting Circuit (see page 11 of SM) there might be a soft pull up to 5 and 6, and at the output pins 9 and 10, but not enough power to provide good output.
BTW, the DC voltage at pins 9 and 10 should be about +24vdc.

EDIT: more info
 
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Notice that the expected DC voltages are written on the schematic at strategic places for the right channel and should be the same at the corresponding places in the left channel. I am looking at page 43 of the SM from hifiengine.com.
 
merlynski said:
:lurk:
Check the Fuses (1.5A), the +50v supply also comes in on pin 17 through the Muting Circuit (see page 11 of SM) there might be a soft pull up to 5 and 6, and at the output pins 9 and 10, but not enough power to provide good output.
BTW, the DC voltage at pins 9 and 10 should be about +24vdc.

EDIT: more info
Click to expand...
Thanks, pin 17 from the mute circuit I'm getting +44.9V and on pin 9 (+21.5V) and pin 10 (+39.3V)
 
Verify that the POWER SUPPLY VOLTAGES are spec'ed +/- 5% @ 120VAC Wall voltage. If you have a Multi-voltage unit set the voltage indicator to 120V. If your Wall Voltage is consistantly 124VAC and > use the 130V setting. If voltages are off, rebuild the Power supply 1st. Caps, Transistor, Zener, and Diodes if leaky. Power supply in the 525 is very simple and not a lot of parts to replace. But it's mounted upside down on the bottom part of the chassis
where it cooks (albeit slowlycompared to a 1010) but it cooks.

IIRC the B+1 feed branches off at the Main Filter cap, one side to pin 17 and the other to the 1.5A Fuses for pins 5 & 6. This may account for some of the difference in voltages, but I would suspect a shorted or corroded component on the Fuse or main boards. Pull the Fuse for Pin 5 and take DC voltage on 6 and 17. Then re-insert 5's fuse and pull 6's. Re test. Post the voltages. Check the Voltages on BOTH SIDES of BOTH FUSES(Black to chassis) with both of them in. Post Voltages. You could have a faulty fuse or a corroded/loose fuse holder or a Cold Solder Joint on the Fuse holder.

Check the wire from the B+1 tap on power supply, thru the Main Filter Cap and to the 3 pins it feeds, look for Pinching between a washer and the chassis, or other components, or breaks in the insulation.

Check continuity from pin to pin in the circuit (Starting at B+1 on the POWER-SUPPLY, thru the 3300uf/63V Main Filter Cap, to each of the destinations (Pins 5 & 6 pull the fuses and go up to the fuse holder, and continue on from the other side of the fuse holder to pins 5 & 6).
 
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larryderouin said:
IIRC the B+1 feed branches off at the Main Filter cap, one side to pin 17 and the other to the 1.5A Fuses for pins 5 & 6. This may account for some of the difference in voltages, but I would suspect a shorted or corroded component on the Fuse or main boards. Pull the Fuse for Pin 5 and take DC voltage on 6 and 17. Then re-insert 5's fuse and pull 6's. Re test. Post the voltages. Check the Voltages on BOTH SIDES of BOTH FUSES(Black to chassis) with both of them in. Post Voltages. You could have a faulty fuse or a corroded/loose fuse holder or a Cold Solder Joint on the Fuse holder.

Check the wire from the B+1 tap on power supply, thru the Main Filter Cap and to the 3 pins it feeds, look for Pinching between a washer and the chassis, or other components, or breaks in the insulation.

Check continuity from pin to pin in the circuit (Starting at B+1 on the POWER-SUPPLY, thru the 3300uf/63V Main Filter Cap, to each of the destinations (Pins 5 & 6 pull the fuses and go up to the fuse holder, and continue on from the other side of the fuse holder to pins 5 & 6).
Click to expand...
Thanks for your help, on both fuses black to chassis, reading 44.3V....when I pull fuse on 5 voltages pin 6 (45.1V) pin 17 (45V)..pull 6 voltages pin 6(39.V) pin 17 (47.6)...I'll check the wires.
 
Randy007 said:
Thanks for your help, on both fuses black to chassis, reading 44.3V....when I pull fuse on 5 voltages pin 6 (45.1V) pin 17 (45V)..pull 6 voltages pin 6(39.V) pin 17 (47.6)...I'll check the wires.
Click to expand...
All the wires seem fine, solder joints look good and no breaks or kinks..
 
Randy. I was editing when you wrote your response. I'll take the 2nd pin 6 voltage to actually mean PIN 5. Your feed voltage from B+1 is ok, a slight bit low but ok. You got something on the left side of the amp off pin 5 pulling down the voltage. (Shorted component, a component leg touching the chassis possibly?) Pull (Lift off the pins and rotate it enough to see under it)the board WITHOUT removing the leads (undo the bundle wrapping and loosen the wire bundle to get some slack) and check underneath for sloppy work, overlength leads from components burned traces, etc.).
 
larryderouin said:
Randy. I was editing when you wrote your response. I'll take the 2nd pin 6 voltage to actually mean PIN 5. Your feed voltage from B+1 is ok, a slight bit low but ok. You got something on the left side of the amp off pin 5 pulling down the voltage. (Shorted component, a component leg touching the chassis possibly?) Pull (Lift off the pins and rotate it enough to see under it)the board WITHOUT removing the leads (undo the bundle wrapping and loosen the wire bundle to get some slack) and check underneath for sloppy work, overlength leads from components burned traces, etc.).
Click to expand...
yes I'm refering to 5 being left protection and 6 being right...does that make sense? I'm a newby at this..
 
larryderouin said:
Randy. I was editing when you wrote your response. I'll take the 2nd pin 6 voltage to actually mean PIN 5. Your feed voltage from B+1 is ok, a slight bit low but ok. You got something on the left side of the amp off pin 5 pulling down the voltage. (Shorted component, a component leg touching the chassis possibly?) Pull (Lift off the pins and rotate it enough to see under it)the board WITHOUT removing the leads (undo the bundle wrapping and loosen the wire bundle to get some slack) and check underneath for sloppy work, overlength leads from components burned traces, etc.).
Click to expand...
Pulled board everthing looks good, however I did replace a burned resistor a few days ago it was R27 18ohm on the main amp board, also replace Q6...the transistor was broke in half, not sure how that happened.
 
Makes lot of sense. Most of the guys are better than me at Solid State. I could never wrap my head around the math for S.S. But the trouble shooting is similar. As the board (AMP) is a Mirror Image, you should be able to take and compare voltages between mirrored component. Start with the Marked bord schematic with voltages and compare them. Tape off the RED PROBE for your meter all the way to the extreme tip. That way if you slip (and we all DO!) you lessen the chances of an "AW SH*T" Moment!

Take voltage drop readings (check voltage on both sides) of R27. Compare with R28 Check the voltages on all 3 legs of Q7. Compare with Q8.
 
larryderouin said:
Makes lot of sense. Most of the guys are better than me at Solid State. I could never wrap my head around the math for S.S. But the trouble shooting is similar. As the board (AMP) is a Mirror Image, you should be able to take and compare voltages between mirrored component. Start with the Marked bord schematic with voltages and compare them. Tape off the RED PROBE for your meter all the way to the extreme tip. That way if you slip (and we all DO!) you lessen the chances of an "AW SH*T" Moment!

Take voltage drop readings (check voltage on both sides) of R27. Compare with R28 Check the voltages on all 3 legs of Q7. Compare with Q8.
Click to expand...
Larry, here are the readings R28 44.3V and 43V on R27 21V and 21V, Q7 B=20V C=0 E=20.6V and Q8 B=37.6 C=0V E=38.3V big differences...
 
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Also Larry, my readings on the P/S are B1 +44.2V.......B2 +25.1V.....B3 +12.2V not bad and little low on B1
 
Are you using a DBT?
What is your AC voltage coming from the wall outlet?
Is this a multi-voltage unit?
The +B (B1) voltage is on the low :( edge of acceptable. With the simple full wave rectifier in this amp and under no load I would expect it to be on the high side (>+50vdc) NOT the low side. Test all the diodes and the transistor on the power supply board. Until we are sure the power supply voltages are good you cannot get reliable readings from the Amp board.

Resistors don't burn for no reason.
No voltage drop across R27 means no current flow, possibly bad Q7 or open fuse.
Q6 broken in half probably exploded from overload.

Check every transistor on the Main Amp board using Echowars' test procedures in this link: https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/

Randy007 said:
yes I'm refering to 5 being left protection and 6 being right...does that make sense? I'm a newby at this..
Click to expand...

When Pioneer lays out schematics on paper with both channels drawn with signal flow from left (input) to right (output) the left channel is the upper path and the right channel is the lower path. In this case on the Main Amp the Left channel input is pin 2, the Left channel output is pin 10, the Left channel power input pin is pin 6.
The corresponding Right channel pins are 1 (input), 9 (output), and 5 (power).
With both fuses good and in place pins 5 and 6 should have exactly the same voltage as pin 17 and the +B pin on the Power Supply board and the + terminal of C5 (3300µF, 64v cap), the main power supply filter. Please compare all of them. If C5 is bad you will have excessive ripple and a low +B voltage.
The chassis/ground pins are not connected to each other on the Main Amp PCB so you must check each pin individually for continuity to chassis/ground. Pins 3, 4, 7, 8 and 19. If any are not connected you will get bad output signals.
Forgive me for being long winded . . . :rolleyes:
 
merlynski said:
Are you using a DBT?
What is your AC voltage coming from the wall outlet?
Is this a multi-voltage unit?
The +B (B1) voltage is on the low :( edge of acceptable. With the simple full wave rectifier in this amp and under no load I would expect it to be on the high side (>+50vdc) NOT the low side. Test all the diodes and the transistor on the power supply board. Until we are sure the power supply voltages are good you cannot get reliable readings from the Amp board.

Resistors don't burn for no reason.
No voltage drop across R27 means no current flow, possibly bad Q7 or open fuse.
Q6 broken in half probably exploded from overload.

Check every transistor on the Main Amp board using Echowars' test procedures in this link: https://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/



When Pioneer lays out schematics on paper with both channels drawn with signal flow from left (input) to right (output) the left channel is the upper path and the right channel is the lower path. In this case on the Main Amp the Left channel input is pin 2, the Left channel output is pin 10, the Left channel power input pin is pin 6.
The corresponding Right channel pins are 1 (input), 9 (output), and 5 (power).
With both fuses good and in place pins 5 and 6 should have exactly the same voltage as pin 17 and the +B pin on the Power Supply board and the + terminal of C5 (3300µF, 64v cap), the main power supply filter. Please compare all of them. If C5 is bad you will have excessive ripple and a low +B voltage.
The chassis/ground pins are not connected to each other on the Main Amp PCB so you must check each pin individually for continuity to chassis/ground. Pins 3, 4, 7, 8 and 19. If any are not connected you will get bad output signals.
Forgive me for being long winded . . . :rolleyes:
Click to expand...
Thanks Merlynski, I am a newbie at this but I would like a good tutor.....sounds like you know what your doing...What I'm going to do is start with the P/S readings for violtages....My AC voltage from my outlet is 123V....P/S (AWR-003) +B1=43.4V B2=25.1V B3=12.2V, (B2, B3 look good...B1 acording to schematic is 4-5V less than what I should have) On Q1 measuring Emitter 30.7V....within tolerence....Collector 33.6V not with tolerance...Base 31.2V within tolerance. On R3 should have 32.5V, I am reading 31.6V.any other voltages I should test.....I kinda would like to start at the souce...Thanks for your help and patience...and yes I am using a DBT.
 
OK, What wattage bulb is in your DBT?
When you turn on the power does the DBT flash bright and then dim way down, or does it keep glowing bright?
Most of the voltages, especially on unregulated supplies (+B) will be low while on DBT because it limits the power input to the transformer, as it is supposed to do to protect other parts in the unit and allow some troubleshooting under power. Once the problems causing excess current draw are fixed the DBT is removed. Those kinds of failures are usually shorted output transistors or filter capacitors, but they may be symptoms of other failures.
More work to do after I get the answers to the first two questions in this post.
When you post lists of results like voltages they are much easier to read if you use this vertical format:
+B1=43.4V
B2=25.1V
B3=12.2V
My favorite things to troubleshoot are Power Supply, Power Amp stage and Protection circuit problems, just what we are working on!
 
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