Pioneer SX-580 Receiver Repair

[Smoky]

Here's a prime example of a well-used Pioneer receiver, mechanically and physically!

The mission here is to get it back up and running and learn how to do an AM and FM alignment.

The exterior has been painted black and the veneer is pealing on the top so I'll be doing a little woodworking too.

I took a look through the perforated vent on the top of the case, and all I can say is, I own a Shop-Vac!

With speakers A & B selected and the volume at minimum I read -30V on the speaker terminals, yes, -30 volts not mV

If I can fix this, I want a badge! or at least a ribbon, as in, PBR

Ultimately, this isn't going to be a "beauty" queen. Just a solid performer!

[andy3055]

You have busted power transistors. It means you may have busted driver stage as well. find the schematic and check all the transistors and diodes in the power amp section.

[Smoky]

Thank you Andy.

Here are the power transistors. I checked beforehand and they cost about $8 a piece.

I can't wait for the day that I own a curve tracer!

[andy3055]

OK, so those are not "power transistors." They are complete amplifiers in one single package for each channel. They are not repairable and a curve tracer will not help either. You will simply have to replace them. There should be a few caps/resistors outside of them in each channel. Check and replace them as necessary.

They are pretty cheap also.

Edit:

Here is a typical schematic with the STK0029. As you can see, it does not have any output caps on the speaker lines. One less thing to worry about. You should not hook up speakers as they will burn up. Power it up and make sure the +ve/-ve supplies are as per the circuit diagram for this model as the loss of either will produce DC on the speaker lines.

http://www.electronica.ro/audio/STK0029.shtml

[Smoky]

Thanks Andy!,

Here is the datasheet of a STK-0029. I do find it a bit confusing as to how to test them. It looks like a complicated circuit.

I like the way the heat-sink bar was able to be removed. It makes great access to the board's components.

If I do a diode test from pin 2 to pin 3 (with the + probe on pin 2) I get continuity. My guess is that I shouldn't.

[andy3055]

All you can do is to check the voltages on the pins as per the schematic, if you can get the Pioneer circuit for the amp.

[andy3055]

Manual is here: https://elektrotanya.com/pioneer_sx-580_sch.pdf/download.html

[Smoky]

Thank you Andy!

Here's what I'll do first. I'll recap the power supply as planned and check other components on the PS board.

Next, I'll install the heat-sink bar and the old power amplifiers and do voltage tests.

My thinking is, no fuses were blown in the receiver, but I may be confusing a failed power transistor's collateral damage and not these power amplifiers.

Good stuff!

[andy3055]

You say "failed power transistors." In this case, there is none. They are all in the STK IC. But, you do have some drivers Q204/203 if I see it right on the schematic on Electrotanya.

Anyway, check all nearby components. The fuses would have blown if the speakers were connected. That is the kind of protection these had at the time. But often they don't and the speakers burn up!

[Smoky]

Here's where I believe is the epicenter of corrosion or where a liquid was spilled. It's right at the base of the main filter capacitors. Those caps are coming out next which will open things up even more.

I literally chipped away a layer of hard goop. I wonder if a glue was used to hold the big caps in place. If so, it made components trapped underneath it to corrode. Look at the tarnish on those jumper wires.

Time to clean this mess up 

[Smoky]

Guys, the area is cleaning up well around those large filter capacitors. I replaced the cruddy jumpers with new silver-coated ones and I replaced that red wire that was burning up against that cement resistor. The sheath of the wire is rock-hard! I used a red striped Teflon wire of a larger gauge for replacement.

Here's the only odd-ball of the night, I pulled that little resistor next to the large 150 Ohm cement one. That little resistor that was trapped under the glue and being cooked is apparently R410.

I got a reading of around 67k Ohms. But if you look at the schematics, it's written as a 100 Ohm resistor.

I'm thinking that I should replace it with a 100 Ohm as written in the schematic. It looks like it was stressed and may be out of whack. What would you do?

*Sure enough! that resistor should be 100 Ohms. I found another 100 Ohm resistor on the other side of the board that's just fine. I'll be testing and replacing resistors, if need be, as I go.

One a side note, notice how none of the components are numbered on the PC board. One must keep a close eye on which part goes where and the polarity of the capacitors

[andy3055]

You seem to be making great progress. Go ahead with the cleaning up as you have started. If those large caps are bad, there is a good chance that it contributes to the DC on the speaker terminals. Just check all the components around the area and you may end up with the STKs being good after all. If not you will need to replace whichever one is bad.

Those old amps/PCBs unfortunately did not have a silkscreen like these days. Only way is to follow the diagram closely which is what you are doing now.

Good luck and keep us posted.

[Smoky]

The two large original 6800uf 35v 85c filter capacitors tested low in capacitance. One measured 5855uf and the other 5535uf. I ordered two 8200uf 50v 105c Nichicon LGY capacitors to replace them. From past experience, I'm guessing they'll measure around 7500uf on the Sencore. I will update the actual values when they arrive Wednesday.

*Here are the caps. The new 8200uf LGY's settled down to ~7300uf!

I'm now in the area of the diodes. Out of these four diodes, two have corroded legs.

The schematics identify these diodes as 30D2 (GP25-D). These are 2.5 amp diodes and I believe they are the 200v version.

What I could find are the Vishay RGP25M diodes.

They are the 1000v version. They are available from Digi-Key and Mouser.

BTW, all of the large capacitors in this receiver are glued down. I mean "really" glued down. Expect to spend some time carefully removing them.

The small electrolytic capacitors that I've removed so far have tested low in value by at least 50%.

As for the film capacitors, I've been randomly pulling them to test on the Sencore meter. Here is a .068uf "K" 10% film capacitor (C170). It not only measures good, it's under 3% with zero leakage!

There are also two 47uf at 25v "CELL" electrolytic capacitors by Nippon Chemi-Con (C206 & C207). Could this mean low-leakage or long-life?

There are also about 15 small orange electrolytic capacitors in a variety of values marked "LR."

[andy3055]

Yes, those diodes should work fine. That glue is like the kind of stuff you use to patch bicycle tubes with. Over a period of time it gets very dry and hard though.

Pay special attention to the electrolytics and before you put the STKs back in, check the voltages on those points where the legs go.

[mzacharias]

The STK packs can be tested for shorts between pins 2 and 3 and between 8 and 9.

Original STKs of this type are long discontinued and any new ones you find are Chinese FAKES.

These COUNTERFEITS rarely if ever perform to original spec. They have inferior internals; I have seen severe notch distortion right out of the box, and I have seen total failure at less than 1 watt output power.

Look for good used pulls, although even these would be hard to find except in a working receiver you might buy on eBay. The 0029's were used in various models.

[poot36]

You can build a replacement STK pack with better components.  Link here: https://audiokarma.org/forums/index.php?threads/stk-0050-replacement-for-sx-780-and-others.721181/page-21#post-11612519 and here: https://audiokarma.org/forums/index.php?threads/stk-0050-replacement-for-sx-780-and-others.721181/

Video of one of them being built:


Good luck.

[Smoky]

Poot36, You blew my surprise

I sent an email requesting just the custom PC boards because the SX-580 has such a huge heat sink that I'm going to bolt the transistors directly to it. I won't need the aluminum plate.

I also plan to remove the 10-pin connector on the main SX-580 PC board and use the pass-through holes for jumpers instead.

It should look real clean.

Anyway, I was able to get another 20 capacitors replaced last night. I match all pairs. You can see the black 10-pin sockets that will be replaced with jumpers. I'm also modifying the heat sink bar so it can just lift straight up and out for easy repairs in the future. The area around the diodes looks much better too.

WooHoo 

I made a special cradle to accurately solder all components to the board. The board is also spaced a distance up and away from the transistors too. I selected the lower 150 Watt ON Semi bipolar transistors over the suggested 200 Watt versions. This Pioneer is only rated at 25 Watts per channel anyway

Installing the modules is a cinch inside of a Pioneer SX-580. The heat sink comes in and out in a minute when 6 to 8 screws are removed. All that needs to be done is to line up some holes by eye and through-bolt the parts to the heat sink. I used stainless fasteners with just lock-washers. For extra insurance, I put a dab of paint on the threads to keep the nuts from loosening. You can also see where I de-soldered the black connectors from the main PC board. Now the cement resistors and jumper wires will get attached with ease.

Make marks on the heat sink with a felt marker where pins 3 and 8 align on the main PC board. That way, the 0.22 Ohm 5 Watt cement resistors can be installed pre-bent to make their connection easy.

[Smoky]

Guys, this is almost as good as a classic Sherlock Holmes murder mystery

When putting together the new Power Pack modules it is imperative that no continuity exist between the new transistors and the heat sink they are bolted to. Special plastic shoulder washers and isolation pads are required and are used. I had no continuity and the transistors remained isolated from the heat sink after they were bolted in.

Get this! As soon as I soldered the new jumper wires of pins 1 and 2 of the new Power Pack module to the main PC board of the SX-580, my DMM rang out its "continuity" tone for transistor Q1's collector to the heat sink!

The same thing happened when I soldered the new jumper wires of pins 8 and 9 which made the collector of Q4 ground to the heat sink.

Both the left and right channels respond the same.

Remember now, the problem with this receiver originally was that I was reading over 30VDC at the the speaker terminals.

This leads me to believe that the new modules are indicating that there still lies a problem/short in the main board of the SX-580.

Could I be right about this?

Up to this point, no electrical power has been applied to this receiver.

Here are the schematics to the SX-580 and the modules.

I'm guessing that the problem is beyond the new Power Pack modules and more towards the direction of the speaker terminals.

[andy3055]

So, did you check the power supply voltages (that come to the holes where the jumpers go in) before you connected the module to the main board? If not, remove the jumpers and check that first. If there is a short anywhere it will blow some fuse which is better than blowing expensive parts. Make sure you have the -ve and +ve 28 volts (or whatever the rails are supposed to be) are all good.

You should also check if there is a short to the ground from the "power in" connections on the module. Check them on both directions.

[Smoky]

Thanks Andy!

I took "actual" voltage measurements at the holes after the new electrolytic capacitors were installed, no Power Pack modules were installed.

*The voltages printed on the schematics are in parenthesis:

Pin 1, -28.8        (-1.2v)
Pin 2, -29.1        (-28v)
Pin 3, 0              (0v)

Pin 8, 0              (0v)
Pin 9, +29.1       (+28v)
Pin 10, +42.9     (+1.2v)

The schematics read that I should have -1.2v at Pin 1 and +1.2v at Pin 10 but I imagine that would be with the Darlington Power Packs installed. Should the voltage read the same at Pin 1 and Pin 10 no matter if they were installed or not? If Pin 1 and Pin 10 should read -1.2v/+1.2v no matter if a modules are installed or not, there's a problem right there. No kidding, what would make the -1.2v/+1.2v shift to -28.8 and +42.9? In the schematics you can see the +41.7 rail nearby in the circuit.


I just tested Pin 1 and Pin 10 on both new modules. I do not get continuity to the heat sink or to the chassis ground in either direction.

I believe the new modules are good to go.


All fuses check good.


I'm in the process of lifting legs of several diodes in the area to see how they test out of circuit.


I love this stuff, we're going to fix it!


*Update* I spent a little more time this afternoon going around the main PC board of the SX-580 and here's what I discovered. With the new Power Packs detached, I did a continuity test from the six holes of their connection to the main PC board to chassis ground. Get this, two holes showed continuity, Pins 2 and 9, the same two holes that give me proper voltage when the receiver is on! Could this be normal after all?

[andy3055]

Yes, checking the diodes etc. is a good idea.

Check Q 303 and 304.

[Smoky]

Thanks Andy!

Q303 and Q304 test good and so does a slew of diodes that I removed from the circuit.

I think what holds key here is what effect on the published voltages does the Darlington Power Packs have when they are removed from the circuit.

The notes on the schematic read that the voltages are taken with the power on and with no input to the receiver. It's just sitting idle.

I am trying to get a hold of someone I know who owns a SX-680 that may be willing to pull his Power Packs and measure the connector pin slots. The SX-680 is almost identical to the SX-580 except that it uses the STK-0039 Power Packs.

[andy3055]

Those voltages may be correct. If you check the diagram you see pins 1 and 10 (shows as 0!) are the collector and the emitter of that 1st transistor in the package. Since you did not check the original STKs, why not hook up one of them and see if you still get the DC on the speaker terminals? Since you have replaced some caps etc., I am thinking they might still be good. I know it is a pain to get it on and off the board 

[Smoky]

Andy,

After reading 30 more pages a second time on AudioKarma, I came across a post where a 1K Ohm resistor is placed across Pins 1 and 3 and Pins 8 and 0 on the main PC board to check voltages without the Power Pack modules installed.

This is good news!

With the 1K Ohm resistors in place, here are the voltages.

*The voltages printed on the schematics are in parenthesis:


Right channel

Pin 1, -5.1      (-1.2v)
Pin 2, -27.4    (-28v)
Pin 3, 0.0       (0v)

Pin 8, 0.0       (0v)
Pin 9, +27.4   (+28)
Pin 0, +5.2     (+1.2)

Left channel

Pin 1, -4.9      (-1.2v)
Pin 2, -27.4    (-28v)
Pin 3, +0.2       (0v)

Pin 8, +0.2       (0v)
Pin 9, +27.4   (+28)
Pin 0, +5.3     (+1.2)


I went back to each position 3 times. The voltages remained the same and didn't budge.

To me, this is good and going in the right direction.

I have one transistor on order, Q502. It was the only odd-ball component that seemed to fluctuate when I tested it in circuit earlier in the capacitor replacement phase. It is called out in the schematic as a 2SC945A but a 2SC1815BL was installed in this receiver. I ordered another C1815BL. We'll see if a new one has any effect on the voltages when it's installed.

I will leave everything as it is until then. Also, to maintain the accuracy of future voltage tests, I'll monitor Diode D401 so that it measures 45.6v (as per schematic) by adjusting my Variac.

Any comments on what you see in the numbers?

[andy3055]

That method of inserting a resistor to check the voltages is great. Those numbers look ok to me. There are slight differences but I think those might be dependent on the many other components in the circuit. If your measured numbers in parenthesis were way over the specified, I would have worried.

What is the next step you plan after you replace the transistor you have ordered? I wonder if we can keep the output transistor legs off the board and power it up. This way, we keep the power transistors safe. It might be easier said than done though. Just a wild thought!