Asking for help on a blown channel on Pioneer SA-510

[Dan75]

Hi, guys,

There is a Pioneer SA-510 (Blue Line series) here that I sold to someone and I got it back because he insisted on that
The reason was that he says it suddenly got a blown channel. The right channel is out.
When powered up, it clearly shows that it is blown. The VU meter does not show output either.
I checked inside for visual damage but couldn't find anything so far.
The thing that I did find is that fuse 3 is done for.

So before I go any further, I wanted to ask for your expertise on repairing this and ask for the next step.
My guess is that the next step could be checking the output transistors.
Can this be done with a MM meter, set in Ohm mode, black probe on the heat sink and the red one on the collector of the transistors?
And perhaps other components like diodes, but which ones

Have added the schematic to this message.
(Note: it is a EU model.)

Thanks,
Dan

[bob91343]

I didn't bother looking at the schematic but if a fuse is blown, an output transistor failure is likely.  A simple ohmmeter test on the transistors will show which one or ones are blown.

Having said that, replacing blown output transistors is a mistake unless you verify the driver circuitry and bias network.  There may be thermistors as well.  Otherwise the new transistors may fail.

[Dan75]

I measured the transistors but couldn't find a fault. I took out another multi-meter with a lower Ohm mode than the one I used earlier. Maybe the other (a cheap one) isn't that great, because it did not show any readings in the lowest mode.
So, I used the other one and that one shows readings on all collectors of all 4 output transistors.

This result, combined with the fact that I did not trust the buyers remark because he told two different stories about what happened to the amp to me I decided to just replace the blown
fuse and see what happens. Maybe not the best action but because the fuse protects the unit I thought that it was worth the shot and.... it works just fine!?

So, what may have happened to it and how it was handled about, stays a guess...

Is it a good move to recap the unit just for the sake of faulty or degraded electrolytics?
If so, are there area's in the amp that need more specific rated caps (ESR, etc) ?

[sean0118]

So, what may have happened to it and how it was handled about, stays a guess...

They probably had a short in the wiring between it and the speakers, or they tried to hook it up while the amp was on. 

I had a similar experience, I bought a broken Rotel amp for $5, replaced both output fuses and it worked fine.

Just to be safe, with the speakers disconnected, check for DC on the outputs, should only be a few 10mV or so. I assume it's okay if it sounds okay, a large DC offset will blowup your speakers.


edit: With regards to capacitors it's really up to you. If they are a good brand I'd probably leave them. If you want to do a recap I think any moderately low ESR, long life capacitors from Nichicon, United Chemicon, Rubycon, Kemet etc would be okay. I've been sourcing them from LCSC, seems pretty well priced for small quantities.

[Dan75]

Hi Sean,

That is my guess too.
He didn't know how to connect the speakers to it, I tried to explain to him about the speakers connections on the back as this amp has two connections, A + B.

Being not a novice on electronics, I just checked for the first time a DC offset.
I took my MM, set it to 2V= (DC) and on the left channel I got: .009 / .010
and on the right channel I got: .006 / .007
So I guess that is ok. Measured after powered on for about 5 to 10 minutes.

Do you have experience with the quality of MM's? I have one that seems to go all over the place, when put in the 2V mode it shows all different numbers on the display when not in use.
Is it just sensitive in picking up frequencies in its surroundings?

[sean0118]

Do you have experience with the quality of MM's? I have one that seems to go all over the place, when put in the 2V mode it shows all different numbers on the display when not in use.
Is it just sensitive in picking up frequencies in its surroundings?

I don't know as much about multimeters as others on here, you could checkout Dave's multimeter shootout videos though. But seems yours is working correctly, those measurements look good, probably just jumps around from stray fields when unconnected as you mention. 

[Dan75]

Thanks! 
I will use the amp for a while to test how he holds up for time being. Other than that I don't know what else I can do about it and resell it once more to a more careful user this time.

[andy3055]

Thanks! 
I will use the amp for a while to test how he holds up for time being. Other than that I don't know what else I can do about it and resell it once more to a more careful user this time.

Yes, don't sell it to the same person.  Obviously he doesn't know how to do some basic things.
When I was much younger, there was a guy who worked on a ship who brought an Amp home. These guys had parties and would blow the thing regularly. I found that he was connecting speakers to both channels all the time thereby, lowering the impedance. At one point I had to rewind his speakers. The voice coil formers were looking like charcoal! In the end, I disabled the B channel. That did not help as he twisted two speaker wires and showed them on the remaining channels! After that, I refused to repair his amp.

[Dan75]

Hi    @andy3055
Yes, you're right, some are really not knowing what the heck they're doing.
One giveaway is the glazed look in their eyes when you explain something, you can almost hear the crickets chirp 

You mention that you rewound speakers, well that is somewhat interesting, I wonder if it is possible to rewind the damaged coil of the motor from a Dual 1019 turntable.
It got damaged whilst taking it apart for servicing. The prying tool got away and ruptured 2 windings. Yes I can help things to bits too 
It is lying around so long now that I recently thought of parting out the unit as a donor, but if it could be salvaged that would be great.
Only thing is wondering to determine how many windings it has now and match that.

Dan

[andy3055]

Winding those motors should not be that hard. If it has just 2 coils, it is a piece of cake. If it has more than that, it is still not a problem. Just needs a little more time. Post a picture of the interior of the stator if you can.

[Dan75]

the damage is on the top half, it is dented and a couple of wires / windings snapped

[andy3055]

That one is an easy fix but you have to wind a new coil, since it is more than just 1 or 2 turns. Just see if you can get the same Guage of magnet wire and cut the thing across that coil. You can then straighten the two sides and pull it out. Not sure if they have put any varnish. If so, it might be a bit hard but if you are patient, you can pull it out. Count the number of turns and just make a wooden former to wind a new coil. Just note down the way the coils are connected to make the right polarity. I think it is a 4 pole configuration. If so, the connection will be such that one will be cw and the next ccw. Cw, ccw,cw and ccw.
I can't see the real damage though. If you are sure, only a couple of turns are damaged, you can carefully separate them and patch them. Just make sure to patch each end on the right to the corresponding end on the left. Make sure to insulate them from one another and the rest. You can use a smooth plastic piece to lift them up. Slip some sleeving or heat shrink on either side and pull them over the joints afterwards.

[bob91343]

Back on topic, replacing electrolytic capacitors on old gear is a controversial subject.  If the current ones don't run warm and the ripple is low, leave it alone.

If we are wandering off topic, I have a vintage Pioneer dual cassette deck, top of the line, that needs motor work.  I don't want to fix it but if someone would want to trade me something for it I could be interested.

[andy3055]

Interesting! I have Pioneer single deck and can't remember when I used it last. It could very well be the belts and/or clutches. I wish I was into it.

You are correct about the caps in these audio stuff. If it is working OK, I would leave it alone. If at all, I would replace only the power supply caps. But if you are selling it,  why bother?

[bob91343]

I had a similar situation.  A friend had a Fisher integrated amplifier and its power supply filter capacitors were running almost hot.  I told him that was a time bomb about to explode.  He ended up selling it to someone who probably could take care of it.

[andy3055]

Those amps were easy repairs. My first amp was one that I built myself after a Pioneer FMB100 tube amp. It had ECL82 push-pull output stage. I still have the schematic. Mounted the tubes horizontal to make the height 3 inches!
Fun days 

[Dan75]

Hi, Andy and Bob
Thanks for your elaboration on the coil windings. As I live in Holland, resources are more scarce to find these kind of things like copper wire. I did a search some time ago but that didn't give much results.
If it will become a thing of sourcing overseas, then it will probably not worth it due to the total costs.

Maybe better indeed for this to start a separate thread to stay on topic.

As far as the recap goes, I do want to flip it, it sounds great as far as I can tell now. So what ever happens after selling it, is out of my hands. If a cap goes then it could be the next day, the next week or perhaps after some years. Who knows.
But I always do a visual check to see if I can find something odd like a leaking or bulging caps. There are maybe 2 that have a minor rising, but I wonder if that really is a faulty going cap or that it is how it left the factory. I am not sure if the electrolytic capacitors are always flat on their tops. Sometimes you'll get fooled by some just by how they were manufactured. For example, the larger coupling caps in this Pioneer have that plastic on top instead of aluminum(?) and that plastic usually is not entirely flat.

But indeed it works, so I'll leave it as is. Have enough other things on the shelf to wrap my head around 

I am liking of the idea I will have my own build amp some day. Nice that you did that, do you still have it Andy?

[andy3055]

Oh no! Long beore I left Colombo, I sold it off. He was a friend of a friend! He wanted to buy my hand built speakers also but I hung on to them  and sold them with an Akai amp I bought later. This was in the early '90s.
Yes, open a new topic on the motor and post some close up pictures and we can go from there.

[TimFox]

Do you have experience with the quality of MM's? I have one that seems to go all over the place, when put in the 2V mode it shows all different numbers on the display when not in use.
Is it just sensitive in picking up frequencies in its surroundings?

Some DVMs have very high input impedance on lower-voltage full-scale settings, and use a roughly 10 megohm voltage divider to get the higher-voltage settings.
Also, with nothing connected to the input, an auto-ranging voltmeter will set itself to a low-voltage input range.
With the very high input resistance, and an open circuit connected to the input, the input will drift as the inevitable bias current flows through the high resistance.  Shorting the input (either directly or through a reasonable resistance) should give you a very low voltage reading, sometimes limited by thermal emfs (depending on the metals in the circuit).

[Dan75]

Andy, I will make a separate thread but not right away as I have few other projects going in front of this one.
For example a Dual 505-3 where there is no service manual of to source for info. It has only a very small PCB, but a fairly large resistor starts smoking as soon as I let the motor run.
Guess that either the caps (2 old plastic RIFA) are toast or that the motor is pulling too much current or something.

And as far as the wire gauge  for the new thread goes, I do not have a micrometer to measure such thin wires but maybe a caliper will do.
But that's something for later on.

[andy3055]

Those motors are very solid. Unless the bearings are ceased and/or there is some mechanical lockup, they will run forever. If it is a direct drive, definitely the bearings may be the cause. Belt drives will not load the motor that much to smoke the motor even if the platter bush is dry. So, you must be correct about the caps which is an easy fix.

Yes, you can use a caliper to check the wire gauge. Make sure to burn off the varnish and the coating on the wire before taking a reading. You have to use a very weak flame like a birthday candle so as not to melt the copper!

[Dan75]

Hi Andy, I just opened a new thread about the coil

[andy3055]

Great, I will check.

[Dan75]

Well, I did not expect this to happen. This morning, I got around finishing a simple entry level turntable from the eighties, from cleaning and checking.
I hooked it up to what I thought was a problem free Pioneer SA-510, and to my surprise the right channel was sounding a bit less, with some crackles.
So initially I thought that it was the cartridge on the vintage turntable or something else for that matter. But no, when I switched to cd on the aux channel, the right channel still sounded less.
Also on the meter it is visible that R channel has less output. Played different kinds of music, just to be sure.
I guess I am back to the drawing board on this one. Kinda sucks.... At least now I know that I have to eat my words in saying that the buyer was incapable of hooking it up correctly.
Opening up the thread once more I guess. Don't know where to go from here though, I have been searching for the output transistors, but they aren't available anymore. If they need replacing that is.

[andy3055]

If you have a scope, you can feed a known signal and start probing identical points on the 2 channels to compare. You can always get some equivalents for the transistors if need be.

Keep the speakers disconnected for time being.