Pioneer SX-950 was working, has lights but zero sound now (advice?)

Tony Frische

New Member
Hi,
New to Audiokarma.
I have a SX-950 that I took out of storage. I hooked it up to three sets of speakers and tested them for a few hours off and on and it was working beautifully. That evening I turned it on and there was no sound. No static or anything. Just lights. I could see the meters were moving too.
Can anyone explain what I should test or check?
Thanks for any input. Tony
 
No speaker relay click. It's like there are no speakers hooked up at all. I work a 24 hour shift so I won't be able to put a voltmeter on the speaker outputs until tomorrow/Tuesday afternoon but I suspect they aren't receiving anything.
 
With the set turned on:
Check the Service manual for setting the DC Balance and Idles. You only want to check the readings first.
Report the voltages you see.
Tip:
Take the readings from all the pins on the protection board (As well). This is helpful in a few more ways, but remember, there are AC and/or DC voltages at the protection board pins. Depending on what pin your checking.
Use the Service Manual scat as a guide.
Use a DMM probe that is covered to the tip, resisting the need to short out two pins at the same time. No reason to make matters worse.

The power supply voltages can wait until you check the amps, but if you have confidence check them and report.
 
Pretty sure you cannot run 3 sets of speakers at the same time at 8ohm, unless they are all 4ohm. That might be your issue. I've had this issue before with a 1050..
 
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I don't think you can have three sets of speakers at the same time. This may be a stupid question, but do you have all three speakers selected? If you do deselect one and see if that works.
 
I took it as, he was trying three set of speakers (One at a time I hope).
 
The 1250 does not allow you to select more than two at a time. I assume the lower powered SX's do the same.

BTW three speakers in parallel at 8 ohms each is 8/3 ohms load. 3 at 4 ohms is 4/3 of an ohm. :yikes:
 
Downloaded SX-950 Service Manual and checked, only two pairs can be selected at one time, if all three buttons are depressed NO sound will be heard.
 
Hi All,
Sorry it took awhile to get back; I've been working a bit of overtime. Anyway, I've watched some videos on YouTube and have identified different components.

I did try three sets of speakers at one time and it cut out but then I only used two and was working fine. That is not the issue.

So, Zebulon, I have checked the readings on all the pins from the Power Amp Assy (AWH-050) and the Protection board (AWM-062). I'm assuming I tested the pins correctly by checking voltage on each pin while grounding the negative prong.
Can you tell me what I compare these figures to? Does this make sense?

My values were: Power Amp Assy(AWH-050) numbers 1-15 (-51.7 -51.7 0 -.9 -.9 0 52.1 52.2 0 15.8 15.8 15.7 15.7 51.0 -51.0).
For pins 16 - 30 (-51.6 -51.5 0 -.9 -.9 0 52.4 52.4 0 15.0 15.0 15.0 15.0 51.1 -51.2)
For the Protection Board (AWM-062) pins 1-12 I got: (15.89 -13.21 15.15 0 15.87 15.84 15.11 15.14 -.99 -.99 -.99 0).

Two more things: I noticed some bulging capacitors on the Power Supply Assy (AWR-101). I don't have the equipment right now but I see from other posts that I can get what I need on mouser.com.
Then, I recall that the morning of the day my receiver went out the treble and bass knobs did not have any effect on the sound. I didn't care at the time because the music sounded beautiful anyway. Should I assume that is a symptom of a problem on the Equalizer Amp Assy (AWF-011)?

Still enjoying figuring this out. Tony
 
Hi All, (Part 2). I compared my values to the values I could decipher on the schematics. Looks like pins # 1,4,5, 19 and 20 on the Power Amp Assy and #9-12 on the Protection Assy are off.
Does it make sense to start replacing components around those junctions? Cool. Tony.
 
If it were mine, I'd start by restoring the PS and protection boards, they most likely both need it (transistors and electrolytics at a minimum). Then check voltages. After that I'd proceed with the rest of the boards, amplifier, then upstream.
 
Re: tone controls not working - there is a switch that turns OFF the tone controls and lets the audio go straight through. In the middle of the tone control knob and lever group.

Please don't use that reporting format again, it causes eyestrain, neck strain, repeated errors in checking, discourages engagement in the discussion, and takes me just too much time to sort out for me or anyone else.

(AWH-050) numbers 1-15
pin 1 -51.7v DC
pin 2 -51.7v DC
pin 3 0v DC
pin 4 -0.9v DC
pin 5 -0.9v DC
pin 6 0.00v DC
pin 7 52.1v DC
pin 8 52.2v DC
pin 9 0.00v DC
pin 10 15.8v DC
pin 11 15.8v DC
pin 12 15.7v DC
pin 13 15.7v DC
pin 14 51.0v DC
pin 15 -51.0v DC


(-51.7 -51.7 0 -.9 -.9 0 52.1 52.2 0 15.8 15.8 15.7 15.7 51.0 -51.0).
For pins 16 - 30 (-51.6 -51.5 0 -.9 -.9 0 52.4 52.4 0 15.0 15.0 15.0 15.0 51.1 -51.2)
For the Protection Board (AWM-062) pins 1-12 I got:
(15.89 -13.21 15.15 0 15.87 15.84 15.11 15.14 -.99 -.99 -.99 0).
pin 1 15.89v DC bad
pin 2 -13.21v DC good
pin 3 15.15v DC
pin 4 0.00v DC
pin 5 15.87v DC
pin 6 15.84v DC
pin 7 15.11v DC
pin 8 15.14v DC
pin 9 -0.99v DC
pin 10 -0.99v DC
pin 11 -0.99v DC
pin 12 0.00v DC


AWR-101 board, these are regulated voltages, unless otherwise indicated. the voltage readings are ground referenced:
pins 2 & 3 +5.4v dc regulated
pins 4 & 5 +13.9v dc regulated
pins 6 & 7 +51.5 v dc regulated this is ok on yours
pins 8, 9 & 10 +36.5v dc regulated seems to be missing
pin 11 +28v dc regulated
pin 13 -13.5v dc regulated this is ok on yours
pin 14 -51.5v dc regulated this is ok on yours
pin 15 -19v dc regulated
pin 17 - 49.5v dc raw unregulated dc to the output transistor circuits,
pin 18 49.5v dc raw unregulated dc to the output transistor circuits

AWM-062 protection board
pin 11 +36.5v dc
pin 2 -13.6v dc
pin 12 7.5v AC
pin 1 audio input, good would be dc millivolts, bad can go up to over 30v
pin 3 audio input, good would be dc millivolts, bad can go up to over 30v
pin 5 audio over-current protection input, good would be dc millivolts, bad can go up to over 30v
pin 6 audio over-current protection input, good would be dc millivolts, bad can go up to over 30v
pin 7 audio over-current protection input, good would be dc millivolts, bad can go up to over 30v
pin 8 audio over-current protection input, good would be dc millivolts, bad can go up to over 30v


loosing too much time unraveling and posting this - rebuild your power supply FIRST. At LEAST Q5 is blown, it is undersized for it's tasks, and my recommended replacement for it IS more robust. This is a common failure. The lists are published elsewhere in this forum.
 
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