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Pioneer SX-1050, no sound

Franco989

Franco989

Member
Hi Everyone,

I just purchased my first serious receiver (previous owner of an SX-750/780) but it comes with some problems. There is no audio coming out from any of the speaker channels, including no sound when listening to headphones. The previous owner mentioned that it was working before he placed in storage, after a period of time when he took it out to use it, the above symptoms appeared. Any idea where I should start looking for troubleshooting this thing? I have experience using a multimeter and have done some soldering, but haven't run into this type of problem before. I downloaded the service manual and was thinking it might have something to do with the protection relay, but don't have much else to go on. Thanks for you Help!
 
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tsd71 said:
No relay click? Are the main in pre out jumpers installed in the back?
Click to expand...
Good call, I had to read up on what pre out jumpers were since my other amps didn't have them, but yes they are missing. I took some RCA cables and connected them per the pics I saw but I still didn't get any sound.
 
we really should be putting together a trouble-shooting flow chart (sticky) so we do not have to repeat the procedure over and over again.
The unit has 2 relays, the 1st is the soft-start(S/S), input AC surge. The 2nd is the speaker protection relay.
if the 1st relay does not operate then the 2nd will not as well.
The S/S relay coil is energized by the +60 un-regulated through a V drop R.
Operation is so that when the relay is un-energized the AC line I flows through a big power R (3R3/20W) that is in series with the transformer primary coil.
Once +60 un-reg comes up it energizes the s/s relay to short out the 3R3/20W R
if the +60Vun-reg fails then a safety feature is to blow the thermal fuse that is in series with the 3R3/20W V drop R.
So you need to check these items out first, that and the mains fuse, switch to see if they are okay, thus you need a DMM. Should have a dim bulb tester too.
 
Thanks for the help, I looked under AWR-104 (power supply) and tested for any blown fuses, there weren’t any. Per another thread I also checked the voltages on AWR-103 (power supply assembly) and AWM-090 (protection assembly) my results are below:


AWM 90 Voltage

1 0

2 -13

3 7.5 AC

4 0

5 0

6 0

7 0

8 0

9 0

10 0

11 0

12 65


AWR 103 Voltage

1 24.2

2 79

3 -81.4

4 0

5 12.7

6 12.7

7 -13

8 -61.6

9 -31.2

10 -25.4

11 -25.4

12 0

13 27

14 27

15 33

16 65

17 65.1

18 4.9

19 4.9


From what I can tell the AWR-103 values seem normal, not so sure on AWM-90. I’m currently in the process of building a DIM bulb tester. I have also tried recalibrating the DC balence and Idle Current on the Power Amplifier but this has not fixed any of my problems.
 
Good repair! glad it's working, also look at rebuilding the power supply AWR-103, and the power amp board AWH-047
 
tsd71 said:
Good repair! glad it's working, also look at rebuilding the power supply AWR-103, and the power amp board AWH-047
Click to expand...
Thanks for the tip , just so I have a better understanding since I'm somewhat new to this, what benefits can I expect by capping the boards you listed?
 
The power supply is a considerable heat generator and components will fail eventually,the same goes for the power amp,Not as much heat but should be done to keep this classic running for a long time, band aids usually don't work for very long.
 
tsd71 said:
The power supply is a considerable heat generator and components will fail eventually,the same goes for the power amp,Not as much heat but should be done to keep this classic running for a long time, band aids usually don't work for very long.
Click to expand...
Thanks I'll add it to my to-do list :)
 
Ok after hooking it up to my main speakers I'm noticing that I have to turn up the dial all the way up to to get sound to come out of the speakers, I can then turn the volume down and be able to listen audio at a lower volume.. I'm guessing this is not normal. For example if I leave the dial at 46 (with audio playing from both speakers) then turn off the receiver, then turn it back on I get no volume then if I turn up the volume I get sound from the right channel, If I turn the balance to the left channel and then turn up the volume I get audio from both speakers.. Any idea of what I should be looking into to get this fixed? Much appreciated, thanks.
 
tsd71 said:
The power supply is a considerable heat generator and components will fail eventually,the same goes for the power amp,Not as much heat but should be done to keep this classic running for a long time, band aids usually don't work for very long.
Click to expand...
One other question, I noticed AWR-103 is really not accessible without undoing the wire wraps, any good idea on what wire wrap took i should purchase?
 
Franco989 said:
Ok after hooking it up to my main speakers I'm noticing that I have to turn up the dial all the way up to to get sound to come out of the speakers, I can then turn the volume down and be able to listen audio at a lower volume.. I'm guessing this is not normal. For example if I leave the dial at 46 (with audio playing from both speakers) then turn off the receiver, then turn it back on I get no volume then if I turn up the volume I get sound from the right channel, If I turn the balance to the left channel and then turn up the volume I get audio from both speakers.. Any idea of what I should be looking into to get this fixed? Much appreciated, thanks.
Click to expand...
Most likely dirty contacts in the speaker protection relay. Tap on the speaker protection relay while it's acting up and see if the channels come back in. They can be opened and the contacts carefully and gently cleaned but replacement is always a better option. Make sure you are looking at the protection relay and not the soft start relay.
 
audiojones said:
Most likely dirty contacts in the speaker protection relay. Tap on the speaker protection relay while it's acting up and see if the channels come back in. They can be opened and the contacts carefully and gently cleaned but replacement is always a better option. Make sure you are looking at the protection relay and not the soft start relay.
Click to expand...
Thanks for the advice, I tried tapping on the relay and the sound would either get worse as in both channels would go out or it would improve, I'll try cleaning them, but preferably I would like to replace it. By any chance do you know where I would find a new replacement and a suitable replacement part number? What is on the board is the following "Type MS4U 48VDC ASR-020-0" see image attached. Thanks
 

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