Pioneer SX-750 Receiver - No Sound Output

[artxperience]

Hi there!

I found this forum by searching for a problem that I'm having with my Pioneer SX-750. I looked at all the articles that mention my particular model and found only one thread that is somewhat close to my issue, but a bit different HERE.

To best describe the problem I have posted the video of my issue:

I've had this receiver for about 5 years now. When I first bought it, there was a problem with the balance knob and i had to replace it. While I did that, I deoxidized all the control knobs (resistors? not sure about the term) to ensure their the longevity. Everything has been working flawlessly until about a few days ago. The sound stopped outputting on both channels on both A and B groups (and Phones output). The only sign of sound is when I crank up the volume about half way then you hear the faint echos of a distorted sound or beat.

Everything powers up properly, the click is heard when you power on the unit. I tried all the inputs (FM, AUX, Phono, etc) but the problem seems to persist. I would appreciate any guidance into troubleshooting this unit.

Thanks in advance!

~ArtXperience

 

[onemug]

Welcome to AK.

I've seen/heard a lot times that this problem gets solved by working the 'tape' monitor switch back and forth several times. Do both if there are 2 of them. If the 750 has pre-outs on the back, remove and insert them a few times...power off of course.

I know you cleaned the controls 5 yrs ago but stuff happens. Good luck.

 

[artxperience]

Hi onemug! Thanks for your reply. I tried working the switch but to no avail. This unit does not have the pre-outs on the back. I tried working all the knobs and switches just to make sure that it's not a bad connection somewhere. But I think the problem might be a bit more serious than that. How to I check on the board where the problem lies? Is there a way to see if some capacitor went bad or the power is not getting to a certain place? I just picked up a multimeter from a friend so I can potentially figure out where the problem is.

Thank you!

 

[Watthour]

It is probably due for a cleaning of the controls once again. If nothing else, doing that will eliminate that possibility from the list of suspects.

The short clip you provided is helpful. There may be problems with the speaker switch, speaker relay contacts, or other connections. One method to help isolate that would be to monitor the unit with headphones with the speakers turned off. If the noise is still present the speaker relay is still a suspect. If the noise is present but less pronounced, that might indicate problems with the amplifier stages.

Also, while there are no dedicated "Pre-Out" jacks on the 750, the tape "Rec" jacks can also be used to monitor the audio upstream of the final amplifier stages.

 

[artxperience]

It is probably due for a cleaning of the controls once again. If nothing else, doing that will eliminate that possibility from the list of suspects.

The short clip you provided is helpful. There may be problems with the speaker switch, speaker relay contacts, or other connections. One method to help isolate that would be to monitor the unit with headphones with the speakers turned off. If the noise is still present the speaker relay is still a suspect. If the noise is present but less pronounced, that might indicate problems with the amplifier stages.

Also, while there are no dedicated "Pre-Out" jacks on the 750, the tape "Rec" jacks can also be used to monitor the audio upstream of the final amplifier stages.

Thanks for your reply, Watthour! I did apply deoxit on all the controls I could get to. This did not seem to make any difference.

I did try to isolate the problem as much as I knew how and tried switching the speakers off and use the headphone output only. The problem was exactly the same. The noise/crackling is really a distortion of the sound that is being output, whether it be FM radio or Phono or AUX. There isn't a hum present or anything like that, just a sharp (painful to the ear) distorted sound that is being output to both A and B and Left and Right speaker channels as well as the Headphones.

One thing to note is that since I started this thread I decided to start slowly replacing the capacitors and transistors on this unit. So far I completed the Power Supply & Protection Assembly (AWR-099) relay, capacitor, transistors and diodes replacements. I was quite hopeful because I've read that C1 and C2 on this board are prone to failure and that maybe this was my problem. But unfortunately the problem still persists. I am really a newbie at this and have no idea how to figure out what the best way to pinpoint the problem is. I did get a multimeter but not sure how to properly use it

If you have any advice for me as to what I can do to figure this out, I would greatly appreciate it. Thank you so much!