Pioneer SX990 issue

gtrplayer76

gtrplayer76

Active Member
Hi folks ! I'm new here ,and I have a question. I have a Pioneer SX990 that the right channel is distorting. Volume seems good it's just distorted. I found the OM/repair manual ,but there's really nothing in it about testing. I can see that someone has been in this before because they added RCA jacks to the A speakers. They also changed one of the 2SC 793 transistors on the power board to a TR 26.
Only thing I've done so far is poke around to see if I hit anything that changes the sound. Nothing yet. I also checked some voltages on these four transistors Q9 ,Q10 ,Q11, and Q12. Base ,and Emitter to ground. 11 ,and 12 showed very little to no voltage. Q9 showed 54volts on one leg ,and 46 on the other. Q10 voltage was fairly even on both legs at around 36-38.
The manual shows the board layout ,and some test points, but doesn't show what to look for exactly. Does anyone know where I can find the values of the test points ?

Thank you !
 
Hi, you'll want to move this to the Pioneer forum, you're likely to get more help there than here with the tuners, since this appears to be an amp issue.
 
Hi,

Here is a thread with some good info on the SX-990.
Post #12 has a pdf with the voltages and useful info shown.

Based on what you've said, it sounds like there are blown outputs. But I would suspect the fuses to blow in that case (no sound). So :dunno:

http://www.audiokarma.org/forums/showthread.php?t=298668

The test points are for doing the amp adjustments and the service manual is more of a guide and mental puzzle than anything else.

(you DO have the service manual, yes?)
 
blhagstrom said:
Hi,

Here is a thread with some good info on the SX-990.
Post #12 has a pdf with the voltages and useful info shown.

Based on what you've said, it sounds like there are blown outputs. But I would suspect the fuses to blow in that case (no sound). So :dunno:

http://www.audiokarma.org/forums/showthread.php?t=298668

The test points are for doing the amp adjustments and the service manual is more of a guide and mental puzzle than anything else.

(you DO have the service manual, yes?)
Click to expand...

I do have the manual/service manual. Thank you for the help. I'll have to feel my way through it I guess.
 
Did you go to the thread I linked, read that and go to post 12 and get the PDF with the amp info on it?
 
Hey folks. So I replaced the two output transistors Q9 ,and Q11 ,adjusted the voltage ,and the bias. I still have distortion in the right channel. The biggest difference I see in voltages are between Q11 ,and Q12. Q11 emitter is 11.8mv ,and base is 600+mv. Q12 emitter is 1mv ,and base is 335mv. I noticed the bias was kind of hard to get settled, but I finally figured I had to make an adjustment ,and let it stop drifting before I made another. I have it now between 45-50mA. Originally they were both running well over 60mA. Something on the right side is still causing distortion, and/or lower volume. Any suggestions ?

Thanks !
 
Its been too long since I worked on one directly (wish one would float to me...)

I did a google search here and got this thread that pretty much outlines all the parts for a complete amp rebuild.

http://www.audiokarma.org/forums/showthread.php?t=485154

I suspect tired capacitors and/or transistors. Finding exactly which bad boy(s) without an o-scope and transistor tester is impossible.

AND, we are assuming the problem is in the amp, not further up stream.

AND, we are assuming you cleaned all the controls well as outlined here.
http://www.audiokarma.org/forums/showthread.php?t=207005
 
Hey moderator,

How about popping this over to the Pioneer Forum and maybe the OP will get lucky and MTF will lean in.

He forgot more than I will probably learn.
 
blhagstrom said:
Its been too long since I worked on one directly (wish one would float to me...)

I did a google search here and got this thread that pretty much outlines all the parts for a complete amp rebuild.

http://www.audiokarma.org/forums/showthread.php?t=485154

I suspect tired capacitors and/or transistors. Finding exactly which bad boy(s) without an o-scope and transistor tester is impossible.

AND, we are assuming the problem is in the amp, not further up stream.

AND, we are assuming you cleaned all the controls well as outlined here.
http://www.audiokarma.org/forums/showthread.php?t=207005
Click to expand...

I cleaned what I could reach. I may have to pull the front panel to get to the other controls. I will check the other transistors, an resistors. maybe replace the electrolytics ,and the 2watt resistors? I also noticed two external caps off that board. They are fed off the positive side of the big can caps C13,and C14. 1000/35 I think. I can't see these on the schematic,but they were installed well if they are not factory. I'll try to get some pictures ,so you can see what I'm talking about. If this moves to the Pioneer forum how do I find it on here ? Well I found the same thing on another post you have above http://www.audiokarma.org/forums/showthread.php?t=485154. He ran into the same thing with the two other caps. See thread #10.
 
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blhagstrom said:
Its been too long since I worked on one directly (wish one would float to me...)

I did a google search here and got this thread that pretty much outlines all the parts for a complete amp rebuild.

http://www.audiokarma.org/forums/showthread.php?t=485154

I suspect tired capacitors and/or transistors. Finding exactly which bad boy(s) without an o-scope and transistor tester is impossible.

AND, we are assuming the problem is in the amp, not further up stream.

AND, we are assuming you cleaned all the controls well as outlined here.
http://www.audiokarma.org/forums/showthread.php?t=207005
Click to expand...


If I were to check the inputs with a scope ,and they look similar would that put the problem in the W15-060 ?
 
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