Pioneer SX-650 Problems

Ren Rivers

New Member
I have a Pioneer SX-650 that I love, but it started clicking even with no volume, and if I turned up the volume, it would play for a few minutes, and then it would click and lose sound, and then come back in a short time, or sometimes longer. I cleaned all of the pots, and done everything I could, but to no avail, so I took into the shop. The repairman tested it, and thought the SP-40W (Darlington) module was bad, so he replaced it. Now he said it plays, but has a loud pop intermittently, and he has not been able to find what would be causing the popping sound. The repairman says he is ready to throw in the towel, because he has so many hours in it, with no luck. Can anyone please tell me what could be wrong, and if what was happening originally was a problem with the SP-40W, or could it have been something else? I don't want to lose this system, it it is a jewel, but I don't know where to turn. Any help would be appreciated.

I am an old Vietnam vet, and can't afford to go out and spend a lot of money on another system, not to mention I bought this system soon after I got back from Nam, and it has countless memories attached to it. So I really would like to have it fixed, Can anyone give some me some clues to help the repairman figure out what is wrong?
 
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Hi, I am another "Old Vietnam Vet". Welcome home Buddy!!

First of all, the SX-650 has 2 SP40W's.
SP40W's have been out of production for a long time, and some of the ones being sold can be questionable.

The Pop can be caused by the SP-40W still original, or the one he put in could be bad.
But I think it can also be caused by the Differential amp 2SA798 which is a double PNP transistor in the same case, with a common Emitter. If he can't get this, he can use 2 individual PNP low noise, high gain preamp type transistors. He will need to measure the voltage coming out of the differential amp to see which channel is causing it. If he sees nothing coming out of each differential (Measue this at pin 2 and pin 6 of the SP40W modules.) He should see the DC voltage level spike up on pin 2 and pin 6 on the bad side, indicating a bad differential transistor, or at least the bad channel causing this problem. The likely culprits would then be the Differential amp 2SA798, or that channels SP-40W.
SP-40 W's can also be replaced by S-40W's
Too bad you weren't closer or I could have helped/fix it for you.
And too bad this unit didn't use S-80W's as I have a bunch of them. But the S40 and S80 have many different pin connections and aren't interchangable.

Tom
 
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Thanks Tom for the kind words, and the offer to help if distance wasn't a factor. I will tell him all of this Monday, because I really want this system back up and running, otherwise I have seen some on sale on e-bay for $120 to $200 and I am not sure I would find a better receiver for that amount of money, if the system was as described, however $40 to $50 shipping makes the price a little steep, unless someone has some other options. It is my 65th birthday today, and that was bad news, got me bummed out a bit.
 
If your unit has 2sa798 transistors, start replacing them with a matched pair of 2sa992. Those 798 have reached the end of it's life, I replace them wherever I find them.

Also, those Pioneer suffer from broken solder, so I'd inspect and reflow the soldering at the boards, specially power supply, power amp and protection board.

There is a whole thread at AK about replacing the 2sa798.

Happy birthday !
 
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First off Happy birthday as well. Knowing your history, you have gone through one heck of a lot to be able to achieve this goal, congratulations.
Fixing this sx-650 is certainly achievable, but it requires some patience and perseverance.
There is a Pioneer forum where you might get more help, send an email to a moderators, ask them to move it for you so more folks can chip in and offer there assistance. many of them do not look in this section, so it is better served to move it.
I'll ask for you.
I have not serviced one of these but many have and can offer their assistance to you.
It is hard to say exactly what is causing the popping, obviously something is going intermittently faulty.
So, I suggest to keep changing components. You are wanting to keep this unit going, so it is probably time to start to change out all the old electrolytic capacitors(ecaps), since they could be the source of the problems. They are usually the cause of many problems with old units. Certainly does not hurt to change them ASAP, to prevent further failures.
We need to look for a current Mouser BOM(bill of material) to figure out what you need to help your tech get the job done. you can search AK for sx-650 and see where a BOM exists.
It would certainly be cheaper for you if you can do the service work yourself. Are you willing or capable to learn to solder, buy a digital multimeter tester(DMM) and do some testing?
The popping could be the power supply on its way out or something else.
It is kind of hit and miss to find the exact culprit or keep on changing parts til you hit on it or just do a complete re-build.
the o/p module(s) could still be at fault as well. We need to figure that out.
But if the output protection relay is not clicking anymore lets try to focus on something else as the cause.
To help isolate, suggest to figure out if the popping is happening on only one channel or both of them. So only hook up one speaker at a time, to see if it is one or both channels doing it.
If it is only one, we can almost say it is not the power supply, if it happens on both channels, it might be a PS issue.
lets start with this channel isolation test first.

Rick
 
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