Pioneer SX-1050

[electra225]

I have owned this monster since the 1970's. I bought it at a stereo store. It had been traded in for a bigger one. This thing kills tweeters for some reason. And it's hard on crossover caps. The only set of speakers that would hold up under this receiver if one was aggressive with the volume control was a set of Peavey studio speakers I had. They were ugly, and the wife hated how they looked, but I never did kill them with the SX-1050. They had 18" woofers and would seriously damage drywall with the bass they would output. I even ran an equalizer on the SX-1050 for some silly reason. It certainly didn't need one. About five years or so ago, it make a noise and lost the left channel. I pulled the case off, to have a look see. Nothing in there that made any sense to me whatsoever. Looks to me like the thing is made in layers. I fixed a little transistor radio one time, but, other than that, I have zero solid state repair experience. Is a Pioneer SX-1050 a device that I should attempt to monkey with, or should I find a trusted repair person to handle the task? I'll probably fix it then sell it. I don't need it anymore. I have a Marantz 2245 that, though not as powerful, is easier to live with and suits my needs just fine. I'm assuming the Pioneer needs caps and that, but I've read about "idle current" and such, about which I know nothing. Any sage advice out there?

[SeniorSteve]

My best educated guess would be that the Pioneer is breaking into oscillations, but at a frequency you can't hear. That would make sense that the tweeters are the speakers being destroyed. Most likely it's happening when the volume control is turned up to a higher level. I know it's a fairly high powered system and I see one here on CL that they want $2500 for it. It's going to be on CL for a LOOOOONG time at that price. Your model Marantz is going for up to $800 here in Minnesota, they really are popular. I had a relative that had a Marantz 2270 which was acting up, that was before I was retired. He ended up taking it to recycle. It's one of those "If I only knew then what I know now" type situations. On the Marantz, it's the distinct look that really sells them, the newer ones without the analog tuner don't sell for a fraction of the price, even if they are higher power and less distortion.

Good luck with the Pioneer, it does sound like it's starting to need a recap.

[electra225]

IIRC, I gave $500 for the SX-1050 when I got it second handed, but not very old. I ran it past its prime, I'm sure of that. It is worth fixing, if for nothing other than its awesome performance and its historical value. I believe they advertised it as 120 watts per channel, not an exaggeration, according to my experience. I used it and the Peavey speakers in my auto restoration shop. That stereo was famous, or maybe infamous if you were my neighbors. The Marantz was my step dad's. Somebody gave it to him broken. He fixed it and it's still going. It probably needs gone thru as well. Is the SX-1050 something I could/should dig into? Do they make kits to rebuild them?

[SeniorSteve]

I'm not sure if there is a "kit" but if you have the service manual you have what you need. You don't have to worry about the paper capacitors like in tube devices, just the electrolytics. Be prepared that there could be upwards of 60 caps or more, especially on the higher end units. There are bipolar electrolytics as well, usually in the power amp and protection circuits. If you want to do a recap, don't let it overwhelm you, do a couple of caps then test. The big issue most likely would be getting access to some of those caps. I don't know the layout of that receiver, but I would assume that Pioneer gave the technician some thought when they built it. The main power supply caps are going to be the most expensive ones. When I recapped the Scott console I had, I think I had less than $20 invested in replacements, but it is definitely no SX-1050. If you aren't planning on using it you could sell it for a lower price with the caveat that it needs an overhaul informing the potential buyer of the potential risks.

Steve

[TC Chris]

This thing kills tweeters for some reason. And it's hard on crossover caps.

We instinctively assume that tweeters die from too much power but it's actually more commonly too little power. When you crank up an under-powered amp too far, it goes into clipping. The sine waves get clipped--flat-topped, lower voltage/more current. It burns up tweeters. Been there, done that. Anybody got an old KLH Model 17 who can sell me a tweeter?

Chris Campbell

[electra225]

Steve, do you believe the repair of the SX-1050 is something you could talk me thru if and when I get stuck?

[Firedome]

Chris: Here you go... $25 each, two currently available:
https://www.ebay.com/itm/274902973529?h ... OSw2jZhFbp~

Seems like a good deal, I just paid $50 ea for ADS tweeter rebuilds.

[TC Chris]

Chris: Here you go... $25 each, two currently available:
https://www.ebay.com/itm/274902973529?h ... OSw2jZhFbp~

Seems like a good deal, I just paid $50 ea for ADS tweeter rebuilds.

Just ordered one! Thanks for the lead.

Chris Campbell

[Firedome]

Excellent! One more vintage speaker to be resurrected!

Just got notice this AM that my ADS dome tweeters are done and being shipped back.
Richard So of Phoenix used to work for ADS and got their parts inventory when they folded.
He can rebuild their tweeters with new ferro-fluid, and I'm v excited to get my L-10s repaired,
imo ADS made some of the nicest sounding speakers ever.

[SeniorSteve]

Greg, the two main areas you would need to replace the caps are the power supply and the amplifier, both main amp and tone control amps. I haven't seen the schematic or photos of the insides, but those two areas would be a good start. If it doesn't hum the main capacitors should be ok, but if if you doing a recap it's nice to get them replaced as well. The big thing is to do a couple of caps, then test to make sure all is well. Another suggestion would be to do one channel until it's done, then work on the other side. This way, if you did have an issue you would have a functioning channel to compare voltages against. If you have a scope, you can put a load resistor on the output of the amp and run the receiver through it's paces. If it is breaking into oscillation, you would be able to see it on the scope. I keep forgetting to check the box to notify me if a reply is posted. Can I change that to default?

[electra225]

Click on your username at the right hand top corner of the main page. That will take you to your user panel. You can change notifications there.

I came across this video on You Tube. This guy has several videos on the SX-1050 and they seem pretty detailed. I have no clue about solid state devices, so this is new territory for me. I have a transistor tester, for what that's worth. The SX-1050 seems to have many of its components hanging upside down, accessible from the bottom.

https://www.youtube.com/watch?v=BP-OZ9UbcFA

He may know what he's doing, but his videos could not be more boring. A lot us useless chatter. Too bad Shango doesn't do an SX-1050 video.

[electra225]

My next step is to get a schematic for this thing and do a little reading and research. Surely, if we can fix a console stereo, we can fix an SX-1050. It has a dead channel, so what do I have to lose? I need to bone up on troubleshooting solid state equipment.

[SeniorSteve]

Thanks for the info on notifications Greg, I've made the change. Also I looked at the HiFi Engine website and they have the Pioneer SX1050 service manual for download. I'll check it out. I'll try to give you some pointers after I look at the schematic.

[SeniorSteve]

Greg, the first thing is to logically figure out where the signal is dropping out. You have pre out and main amp in jacks, so you can eliminate a lot of the circuitry by swapping the channels at that point.

If by switching L and R channels at that point you still have the same "dead" channel, it looks like something in the "dead channel" main amplifier.

If you have one good channel you know the protection circuitry is active and you don't have DC at the speaker outputs and that's a good sign. I recently worked on a Technics receiver and it had an intermittent channel which ended up being the speaker relay contacts being oxidized. Don't forget the speaker switches contacts too.

Edit: If you use the headphones, you eliminate the speaker switch as a possibility.

The higher end receiver just normally don't "go bad" and the switch and relay contacts would be the first place to look. Another hint is your headphone jack is connected to the output of the main amplifier through reducing resistors, so using headphones can be the equivalent of using the speakers with a much less load on the amp.

I did download the schematic from HiFiEngine and it's better than some that I've seen.

[electra225]

Can I still use my signal tracer on this receiver?

[electra225]

Would a kit like this be something to consider? I realize there are no power transistors, relays, or LEDs' for the dial lights. I can see $400 to $500 worth of parts to go thru this, if I need relays and transistors.

https://www.ebay.com/itm/153892667521?_ ... %7Ciid%3A1

[SeniorSteve]

Rather than jump in and go all out, let's just get an idea of what is wrong. You say one side is dead (left), you already have a signal generator - it's the tuner, and if you use an AM station you have a good mono signal. If you want better sound go to FM, but make sure you have it in mono. The reason I'm suggesting headphones first is you eliminate the speaker switch as a possibility. The headphones are connected directly to the output of the amplifiers through a resistor, so if there is signal it will be there. The fact that the one speaker is working (or headphones) means there isn't much of a DC offset to trigger it into protection. That's a good sign, and the same relay does both channels so if one channel triggered protection, both will go off.

Next step is to find out where in the audio chain is the signal dropping. The pre amp out to main amp in is a very good starting place (rear panel jumpers). Normally the jumpers connect the left pre out to left main amp in and same with the right side. To eliminate the tone controls and pre amp circuitry, all that is needed is to get a couple of RCA cables and connect the left pre amp out to the right main in and right pre amp out to the left main amp in. Do this with the power off as there is no attenuator on the main amp. If it is the main amp, the dead channel will stay the same, as it means the pre amp out is working on both sides.

Those capacitor kits are handy, but the only expensive capacitors will be the main filter caps, and if the unit isn't showing signs of hum yet, it can wait. The rest of the caps if all added up should add up to maybe $50.00. It's those two big ones that I can see being up to $30.00 each or possibly more.

Try these steps first to see where the signal is being lost. I'm hoping you have a set of headphones so we can eliminate the speaker switch.

Steve

And yes, a signal tracer could be used to follow the signal. I just want to see where it drops first to eliminate as much circuitry as possible before actually digging into the circuitry.

[TC Chris]

Edit: If you use the headphones, you eliminate the speaker switch as a possibility.

But beware. I've got a Sherwood solid-state receiver that gave me fits. One channel would go out. Couldn't figure out why. Turns out the headphone jack was a switching type--plug in the phone, the contacts opened and the speakers cut out. My receiver had oxidized contacts in the headphone jack so the speakers didn't cut back in after the 'phones were unplugged.

Chris Campbell

[SeniorSteve]

Hi Chris, that's a good point, I''ve seen some receivers that did that. I looked at this one, and to turn off the speakers you have to turn off all three sets. I thought this was a rotary switch, but now I see it is three separate push buttons, one for each set of speakers. The documentation says you can push all three in at the same time, but only two will work at a time. This is quite a nice receiver, and very powerful one for it's time.

I don't know the details of how the one channel stopped working, but the protection circuit is operating (the other channel is working) and there isn't any smoke, so hopefully this won't be a big job. "Oops I think I just jinxed it"

I'm hoping the speaker relay is in a socket and removable, that's my first thought.

[electra225]

I used this receiver longer than I should have without servicing it. I use it primarily to "do my music", process analog material to digital. The switching on this receiver is quite flexible. For probably five years before one channel quit, the left channel, the one that quit, would go out. I could push a button on the front panel (forgot which one, it's been so long) and it would come back in. The push button controls on this receiver seemed like they were dirty. One day I was using it, the left channel made a screeching noise, then some "snap, crackle, pop", then silence. This may have been over five years ago. I substituted this receiver with my Marantz 2245 and find it quite adequate. I used an equalizer on the SX-1050 to process 78's. That would be like putting twin turbochargers on a Hemi. The thing simply eats speakers. IT eats tweeters for some reason. The only set of speakers I ever owned that would stand up to the SX-1050 is a set of ugly Peavey studio speakers. I had to turn the bass down on the SX. It would rattle things off the shelf in the kitchen.

Steve, your approach sounds reasonable, and I thank you. This receiver is still in storage, and my shop is not done yet. So, this project is somewhat in the future, but you have given me insight for a path moving forward. I want to go thru test equipment first when I get my shop done. I believe the SX-1050 may have moved up a bit in priority. I was going to sell it broken, since I really don't need it anymore. It might make a fun project, something I've never done before, and will make a good topic on the forum.