Pioneer SX-1050 receiver restoration

[electra225]

The first thing I need to determine is if the PT is still okay. Something took a dump today when I was doing my baseline check. I don't want to gamble buying $200 in parts if the PT is bad. One relay is a "thump" relay, one relay is a soft-start relay. I think the "thump" relay is still working. If I can determine that the PT is okay, then I'll start with establishing a stable power supply, then go from there. Bill, you are right. If the PT is good, the rest can be repaired. I ran this thing too long after it started acting wonky. I know better.

[William]

If my memory is working, doubtful, I believe Elton purchased a soldering station that had a built in solder sucker. I think it came from Harbor Freight, but I could be wrong on that and if I remember correctly it was not a lot of money. Maybe a PM to him will fill in the blanks of my poor memory.

Bill

[electra225]

Thanks, Bill, that's a good idea. I have a Harbor Freight right up the road, across the street from where I work.

Diagnostic "guidance" on this rig is essentially non-existent. It seems the common practice is not to try and figure out what might be causing an issue, just throw parts at it. If you throw enough parts, or you throw the right parts, that will surely fix it. Just buy a parts kit, install the parts. If you install them all properly, it's fixed. Okay then....

The PT on this thing is different from what I'm used to. There are also no audio output transformers. The front end of this thing appears to be working. The tuning meters move and I could hear the radio very faintly. IF I read the schematic right, it may be due to the fact that the front end has its own power supply. The big 22,000uf @100 VDC filter caps are for the audio section. There are four PC boards that deal with the power supply. One that I call the rectifier board, one that is a regulator board, one is the speaker protection board, one is the soft-start board. The fact that I only have a 22-watt draw indicates that the dial lights and front end only use 22 watts, whereas the audio section must use the remaining 450 watts? It also appears that my suspicion of not having B+ to the audio section is plausible. I am not 100% positive that the PT is okay, but, with all the protection devices, fuses, the soft-start circuit, I don't see how it would be possible to damage the PT by a short circuit. Both the primary of the PT and also four (that I can see) branches of B+ are fused. And, if I am checking the PT correctly with my ohmmeter, it checks okay that way. I'm probably boring you guys to tears, but I use this rambling for reference later if I need it. I'm trying to familiarize myself with the various components and what purpose they serve before I start throwing parts at this thing, which appears to be the accepted practice.....

[electra225]

There are four pototentiometers (pots) on the driver board. These pots, apparently, are known to go open, so they include those in most parts kits. One pot is open on the channel that is dead. Will that open pot kill a channel? What do these pots do, what function do they serve?

[electra225]

The open pot is V1, a DC balance pot, on the schematic and parts list. This pot being open would remove the voltage from the base of Q1, which is an audio amplifier transistor on the driver board, which is in the dead channel. Pots V1 and V2 are DC balance pots, set to 0 VDC. V3 and V4 are idle current pots, set to 50mv after the amp is turned on for one minute, then checked again after 20 minutes operation. V1 being open in this chassis would be like having an open cathode bias resistor in a tube chassis. I'm guessing that no voltage on that transistor base would kill the channel, but I don't know that.....

I am going to have to eat crow on this project. I don't normally have much good to say about AudioKarma. This time, they bailed me out. I have typically said that I never got any usable information from AK. I take that back now with apologies......

[danrclem]

I think this is the desoldering gun that I was thinking of. It looks like it's gone up a lot in price since I priced it a few years ago, but everything else has gone up in price too. If I remember right some of the reviews that I read say that it stops up sometimes and will need to be cleaned. Since you plan on taking a while to do the receiver I don't know if it would be worth paying that much just to do one. Probably not.

Have you tried taking the preamp to amp jumpers out and plugging another amp and preamp in to see which side has the problem? You may have already addressed it in this thread and if you have just ignore this.

I'm probably in the same boat that are when it comes to not knowing what I'm doing. I know just enough to be dangerous.

https://www.ebay.com/itm/177076414437?_ ... R-imvoD2Zg

[TC Chris]

The open pot is V1, a DC balance pot, on the schematic and parts list. This pot being open would remove the voltage from the base of Q1, which is an audio amplifier transistor on the driver board, which is in the dead channel. Pots V1 and V2 are DC balance pots, set to 0 VDC. V3 and V4 are idle current pots, set to 50mv after the amp is turned on for one minute, then checked again after 20 minutes operation. V1 being open in this chassis would be like having an open cathode bias resistor in a tube chassis. I'm guessing that no voltage on that transistor base would kill the channel, but I don't know that.....

If you know the resistance of the balance pot, or can measure it from the non-open end, you could sub in a fixed resistor on the open side and see if that restores the audio.

Chris Campbell

[electra225]

The two DC balance pots that the two other ones come in one of the kits I linked above. What I want to do in the short term is two-fold. One, decide if this project is going to be economically feasible. Then, to gain enough knowledge to be able to troubleshoot this receiver, and just not throw parts at it willy-nilly and not gain knowledge from the experience.

I am going to have to buy certain equipment to complete the project. I need an ESR meter. Shango uses a "Capacitor Wizard" which will check capacitors in circuit, which would be really handy in this project. This device would cost over $200. I need to find a new probe for my little Heathkit scope. Cost unknown. Then I need a solder sucker soldering iron. $50 give or take. Soldering wick braide $20. Dielectric grease $10. DeOxit D5 $20. Parts kit $255 with shipping. Then if I need output or amp board transistors they would be $20 a pair for output, there are 8 total, and $15 for ten transistors for the amp board. Then if I need a rectifier bridge and can find the right one those go from $20 to $80. I have no idea what a PT would cost, but I won't continue the project until I confirm that this one is okay. I need a set of feet for the cabinet. I have a light out in the Speaker B position. LED's would be the way to go there, don't know the cost of those. They want a minimum of $1500 to do this job by a professional, if you can find one, and if I can find one I TRUST, a larger task indeed. I am estimating it will take 100 hours of my time, I'm old, I'm slow, and I'm learning, so it won't be a weekend job. There is a short in the dial lights. They flash when I turn the chassis on its side. I have a dead channel and possibly a dead power supply. None of the kits include caps or transistors for the tuner board. The pros on YouTube recommend doing everything else first, then do the tuner only if it needs it. I need more research on this. My first task will be to familiarize myself with the different types of transistors and their terminal basing. I need this knowledge so I put parts in right. This chassis uses stakes with the wires wrapped around them for connections of the various boards. You take voltage readings at these stakes, then follow on to the first component and so forth. Really easy to maneuver. You can disconnect the various branches of B voltages, both positive and negative, by removing fuses. There is a 10-amp main fuse which fuses the external power provisions and also the primary of the PT. Then each leg of B voltage is fused. Kind of a neat setup.

The balance control, the volume control and the four tone controls all have to be unsoldered from their boards to be cleaned properly. It's quite the procedure to clean the controls. Then there is the component called "the triple diode" between the amp board and output heat sink that has to be removed to get everything apart. This component is not available for replacement. I don't want to put good money into this receiver only to have it all for naught if and when I break this component. I need to find out what it is, what it does, and if it can be reproduced out of discreet components.

[TC Chris]

You can buy feet at Ace Hardware. I found dielectric grease there too, although I had small containers from Heathkit projects. Start by diagnosing with your voltmeter and ohmmeter. Rule out the expensive items and then start replacing things that need it. If you can get B+ off of zero, then you can measure voltages at other stages and figure out what MUST be replaced to get sound.

Chris Campbell

[electra225]

For those who know more about working with solid state stuff than me, which is everybody.....

I have read where it is important to discharge the filter caps before/when/during the replacement of transistors. So does one discharge the filter caps to chassis ground? Chassis ground serves a different purpose in solid state chassis than in tube chassis, does it not? You have both positive and negative rails in transistor circuits. Can a transistor be zapped if the caps are not discharged properly? Would it not be better to disconnect the filter caps for safety, then shotgun the chassis? Can my signal tracer be used with this chassis like it can with a tube chassis? I ask this because I plan to "split" the front end from the amplifier at the "main in-pre out" graphic equalizer connections on the rear apron of the cabinet.

[danrclem]

Greg, I'd hate to give you the wrong answers because I probably don't know any more than you do (maybe less) so rather than possibly giving you a wrong answer, I'll keep my mouth shut.

I know from reading past posts that you don't like AK but that may be the best place to find your answers. I don't care much for AK either but it's probably just a few people that are giving it a bad reputation. I know for a long time I wouldn't even log on there because of certain people there. It looks like there are a lot less people participating there than what they had a few years ago.

There are some people in the Pioneer forum who are very knowledgeable and who are willing to help or at least there used to be. I've saw lots of threads there where they helped people through an entire project. I think it would probably be worth a try.

[electra225]

Danny, I appreciate your comments. I am leaning towards actually joining AK so I can ask for the help I'm sure I'll need. YouTube videos help, and I actually watched one that the receiver they were working on had the same issue and I'm working with. I have specific questions that will need more personal intervention that a YouTube video. AK can't be much worse than ARF when it comes to folks with a high opinion of themselves. You just have to weed thru all that and concentrate on the information you actually can use. The comment made about cleaning the controls may turn out to be some of the best advice I have received so far. Seems like every video I have watched talks about the issues caused by dirty controls. And electrolytic coupling capacitors. I may have found out why this receiver was so hard on tweeters. The DC balance may be off. I want to do some more preliminary investigations before I decide what I want to do. I have tentatively decided to do this project with the equipment I have on hand. I want to control expenses as much as I can. This project will take me at least six months, maybe longer...

[TC Chris]

If you want to discharge the caps, why not use a resistor in series with a jumper wire an just go from one terminal to the other?

Chris Campbell

[electra225]

Chris, to be really honest, I believe I may be over-thinking this a bit.

I have been doing some careful research, since this is an opportunity to both learn something and to mess up royally. AudioKarma has compiled a list of the parts needed to completely restore and repair an SX-1050. There are 296 parts, all available from Mouser. The parts kits available only have 80-something parts included. The kits don't include transistors or diodes for the audio board or the output transistors, nor any parts at all for the tuner board. They don't include the insulators for under the output transistors. They don't include the power supply diodes. They do include both relays, which I likely won't need to replace. I will have to practice navigating Mouser's website, but I'm wondering if it won't be both less expensive and will get me more complete parts if I just order from Mouser "by the board" or as I work on the dozen or so boards in this chassis. Watching the various YouTube videos on the subject yields various opinions of what is necessary to do. Some say replace everything, some say not necessary to replace everything. Who do I believe? I will need to get my old scope going, I'll need it. I really need a dual-trace scope, but that's not gonna happen.

[electra225]

The power transformer seems okay at this time. We'll forge ahead....

[TC Chris]

Good plan. I take a minimalist approach, modifying the old saying as follows: "If it ain't broke (or is likely to be soon), don't fix it." Aim for getting basic function back. Then you can evaluate the sound and decide whether you want to replace more caps and check more resistors. I don't see much sense in shotgunning transistors. If one is faulty, replace it (like we do with tubes). We routinely replace filter caps because (a) the consequences of failure in transformer devices are bad, and (2) they are stressed devices that are known to degrade with age. We replace paper caps because they usually degrade with age and they are cheap.

If you've got one channel with no sound, that means a component is either dead or wildly out of spec. Find it and fix it.

Chris Campbell

[electra225]

"Find it and fix it". That's really good advice. Now if I just knew where to look....

I'm getting warmer. I think. I have been "boning up" on how to deal with transistors. Most of these are the simplest junction transistors, so that's good. There are some little clear doodads on the boards that look like clear capacitors. I need to find out what those things are. I believe I have a basic idea of how this thing is supposed to work. I think I have a decent grasp on how to troubleshoot transistors. I still have no idea how they actually work. Seems to me like that aren't enough parts in one to let it work. No screens, nothing to control the device. I won't worry too much about that, my goal is to figure this thing out enough to get it to work again. I understand why this receiver has been so hard on tweeters. I know about idle current and how to set that. The repair kits that are available are like other kits you buy. They contain the most basic, most commonly needed parts. It's then up to me to figure out what else I may need. Like rebuilding a carburetor. You buy a carb rebuild kit, then you may also have to have the throttle shaft rebushed, may need choke pulls, may need a new fuel filter. Those don't come in a carb kit, but you need them to complete the job. The rebuild kits for this receiver don't have driver transistors, output transistors or most parts for the tuner board. The kits concern themselves with the power supply and audio circuits. They figure by the time you replace 104 parts in the receiver, then power up for test, you'll have a good idea of whatever else you may need.

[TC Chris]

"Find it and fix it". That's really good advice. Now if I just knew where to look....

How to find? C'mon, you know the basics.
1. locate where the problem is--which channel, before/after the volume control, etc. Localize as much as possible.
2. Check voltages from the schematic's values. If no schematic and a stereo, compare voltages in the channels at the same point in the circuit.
3. Or use a signal racer to see where the sound stops. A capacitor in series with a high impedance headphone will do, but you've got fancier stuff.

And I will add 4. Use a bright light and a magnifier so you don't find a faulty red-red-red resistor and replace it with a red-red-orange and head off on a wild-goose chase, replacing perfectly good transistors that aren't working because they're still biased wrong. In other words, work carefully.

Chris Campbell

[electra225]

My first task is to get the power supply straightened out. Then, I need to find out if the DC bias being wildly high is the only cause of the protection circuit relay not closing. The dead channel, at this point, is ahead of the power amp board. It is in the "front end" but not necessarily in the tuner. I really believe it has a dirty control, but I haven't confirmed which one. I found a bulging cap in the power amp board, so that isn't good. There is that intermittent trimmer, which is in the dead channel. I have almost 7 VDC in the speakers on the dead channel, which should be zero. This may be what it kicking out the protection relay and also why it eats tweeters. Who knows how long it's been like that. Pending further testing, the driver transistors and the output transistors appear to be okay, at least not open or shorted. I can only run line voltage to about 75 VAC because the dim bulb gets really bright higher than that. One leg of the power supply appears to have a heavy draw. I'm working on it now, trying to run that down. I need to get a pretty good handle on what the issues are so I can order parts all at once and not have to pay shipping on a little part. This is actually a fun project, and I'm looking forward to finding the culprit.

I'm beginning to see why they offer parts kits and recommend throwing parts at it, then testing. I've also learned that parts other than what is offered in a kit may be needed to complete the repair. I'm fumbling a lot, but I'm also learning a lot. And, Chris, your "resistor band" incident is partially why I'm taking my time at the risk of over-thinking some of this. I don't want to mis-install a part, because I'm not sure I could efficiently troubleshoot it.

[electra225]

I have hit a bit of a snag. The schematic I have, from AudioKarma, is not good enough to be able to read component values and voltages. I took it over to Tres, thinking my eyes or my printer may have been the problem. The schematic is simply degraded enough it can't be cleaned up enough to use. The bulk of the shop manual from AK is plenty good. I want to blow up the schematic sufficient for me to make notes and reference in case I have a problem after I "fix it". Sams does not have a manual for this receiver. I'm not having much luck elsewhere finding one. Ideas?