Pioneer SX-550 Issues

TPN

New Member
So whilst this is a little over my pay grade, I'm giving it a whiz at repairing this beautiful receiver.

I found this at a charity shop and decided to pick it up. At first, it would do the thing that's most common for these SX-550s to do, flicker the power light. I managed to fix that issue, but now have another issue that I must admit, I don't quite understand.

Once I got this to power up, the left channel was highly distorted, and was quite a bit lower in volume compared to the right channel. I've tested all the different inputs, and it doesn't change no matter the input (including radio.) When testing using the headphone output, it works fine. Both channels sound reasonably great. No distortion, and both are same volume to each other.

Now, I am unsure if the outputs for speakers at the back and the headphone use the same circuit, looking at the circuit diagram, it looks like they do but again, I am no expert, just my first repair project on something like this, so I am more than likely wrong on this wrong.

Going with that mindset, I was tracing the back of the board as best I could, and to be quite honest, it doesn't look right to me. It looks like there has been some sort of liquid or something spilt as the back of the board looks quite bad, and some of the traces look as if they have been slightly eaten through with something corrosive. (Included some pictures of the back of the board.)

I will also add that, it's only I guess the audio side of the board that looks this way. Looking at the opposite end of the board, there is nothing on it, it looks fine.

If anyone would be able to shed some light on this for me as to what the issue might be, that would be excellent.

Thank you!
 

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Welcome Aboard!

The photos appear to show possible heating or corrosion in a couple areas. Fortunately, it appears to be minor.

The symptoms you are describing would seem to indicate a problem with an output transistor(s). Noticeable distortion with speakers and almost no distortion on headphones is a classic symptom of damaged outputs and/or drivers. If you have a meter handy it should be a fairly easy analysis. Access to the devices can be a little tight, but if you've been through the power switch you're probably already aware of that:

SX-550OutputTransistors01.jpg



Fortunately, repairs are relatively inexpensive. I've had two 550s in the same condition. The final output stage 2SD526 and 2SB596 devices can be successfully replaced with MJE15032G/MJE15033G - About $1.60 apiece. The driver stage 2SC1211 and 2SA697 can be replaced with KSC2690AY and KSA1220AY, for about 50¢ each. Of course, before ordering parts it will be advisable to completely diagnose the problem(s) and anticipate and upgrades you may want to perform. I have suggestions.
 
Thank you for the response! Gives me something to start with now. I shall look at this over the week and report my findings!
 
So, I had a short little look around today, just wanted to make sure that I am looking at the right thing before I continue. I've included pictures about what I think it is.

From looking around on the internet at the original parts numbers though, I feel that I am wrong.

Thanks
 

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Welcome Aboard!

The photos appear to show possible heating or corrosion in a couple areas. Fortunately, it appears to be minor.

The symptoms you are describing would seem to indicate a problem with an output transistor(s). Noticeable distortion with speakers and almost no distortion on headphones is a classic symptom of damaged outputs and/or drivers. If you have a meter handy it should be a fairly easy analysis. Access to the devices can be a little tight, but if you've been through the power switch you're probably already aware of that:

SX-550OutputTransistors01.jpg



Fortunately, repairs are relatively inexpensive. I've had two 550s in the same condition. The final output stage 2SD526 and 2SB596 devices can be successfully replaced with MJE15032G/MJE15033G - About $1.60 apiece. The driver stage 2SC1211 and 2SA697 can be replaced with KSC2690AY and KSA1220AY, for about 50¢ each. Of course, before ordering parts it will be advisable to completely diagnose the problem(s) and anticipate and upgrades you may want to perform. I have suggestions.

Alrighty, well I finally have got around to checking the parts, and most of them seem to return bad. So, hopefully the order parts will fix that. I shall post an update when all comes and are installed.
 
boards look ok apart from dry loints

I hopefully intend to remember to touch some up when I install some new parts. Seems good otherwise on the opposite board.

I get the feeling that someone has already been in here so maybe some of the joints look bad because of them, I don't know though.
 
It looks like it's been repaired at least once before. The outputs are not matched devices and not the same components Pioneer would have used. At least that what appears to me.
I would reflow all the connections on the main board as well. I wont take that long to do, small receiver.
 
So I've finally got around to replacing the components this Sunday, and whilst it does work still, there is no improvement.



Both channels now have distortion. They do both however sound the same in terms of volume level. The headphone output now also sounds the same as the speaker output.

After a short period of testing, it seems that the right channel cuts out, and the left channel has so noticeable crackle to it.



I can kind of get it to sound decent if I run the volume extremely low on the receiver, and use the phones output into a small stereo amp and use that as the volume control and it does sound decent up until the channels start to crackle or cut out as it be with the right channel.



I have done plenty of testing to make sure that it "shouldn't" be my soldering, mainly tested all links from the new components to most of the traces that I can find for them on the board, and it seems fine, no breakages.



So, looking for some advice on really what to do next. Maybe I am missing something, but not entirely sure my end.
 
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