Author Topic: Asking for help on a blown channel on Pioneer SA-510 (Read 5958 times)

Dan75 · « **Reply #25 on:** October 30, 2021, 07:09:49 pm »

Hi Andy, I do have a scope but never used it. As I am fairly new with electronics, that is road I haven't taken yet.
Not sure if the things works, never tried it out. Found it on a flea-market a few years back.
It is this this one:

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

andy3055 · « **Reply #26 on:** October 30, 2021, 11:41:05 pm »

Wow! That looks pretty old! You may want to power it up and see.

Wallace Gasiewicz · « **Reply #27 on:** October 31, 2021, 11:16:18 am »

Unfortunately your scope has only one channel, Harder to compare with the other channel, you have to just move the probe and remember what the trace was. But it should be really nice for audio work..
15 MHz is just fine for audio. This type of scope is probably better for audio purposes than the newer digitizing ones, I have both types.I would take the cover off first and just look for anything obviously bad first.
You should probably get a cheap 10X probe though, if it fires up without smoke. I like to power old stuff up in the garage in case a big cap goes bang! If you have an auto transformer, you could "warm" the thing up slowly starting with half volts and increasing voltage every five min or so.
If you get any trace on the screen then get a probe and attach it to the Probe Adjust Lug, you should get a square wave on the screen.

Just my opinion, maybe I am wrong about this but:
If the final transistors go in an amp, they usually go in a big way, usually they burn up. So no output at all. They are also hard to replace, since they need to be matched and the equivalent transistors might not be exactly like the originals and especially may require different bias. So maybe the fault is not in the final transistors. (Hopefully)
Wally

Dan75 · « **Reply #28 on:** October 31, 2021, 08:03:24 pm »

Hi guys,

It is old indeed

The specs I found on the internet say it is indeed a one channel scope and is produced in 1972.
I haven't fired the scope up since I bought it, so I don't know if it still is operational but the seller told me it worked. But that could also mean 25 years back?

It came with three probes. I'll try to make an image of them. Been busy today with another project that almost is giving me sleepless nights. A Dual turntable that has a hum in it.
But that is for another topic and time.

I sure hope it isn't a failing transistor but maybe bad caps. I can see that some in there seem a little out of spec, visually that is. Gradually bulging tops. I think I will solder out some of them and run them through my meter, I have a meter that is similar to the Peak ESR meter.

I had noticed that after a while of using the Pioneer the right channel got faulty as I described, but also got back in spec again? It fluctuates, you might say.
Maybe I can hook up a (working

) turntable to the Pioneer and play a audio test record on it to see what it does along a period of time. And maybe make a video of it.

Wallace Gasiewicz · « **Reply #29 on:** October 31, 2021, 08:11:53 pm »

Lots of times intermittent problems are just bad solder joints on the PCB.
Simple but not necessarily easy to find.
I would not think a blown or leaky cap would be intermittent.

Dan75 · « **Reply #30 on:** October 31, 2021, 08:52:56 pm »

Hi Wallace, thanks, I will look into that, maybe there are broken connections. Maybe due to vibrations or degrading material?
I also heard of that some transistors have a thing going on called thin whiskers. Could that also be causing these symptoms?

Wallace Gasiewicz · « **Reply #31 on:** October 31, 2021, 11:16:05 pm »

Probably not whiskers, I think this is not intermittent. My cat is nowhere near you. HA
Really just look for bad (cold ) solder first. Push on different parts of the board with a plastic or wood stick, see if the channel comes up.

andy3055 · « **Reply #32 on:** November 01, 2021, 12:02:47 am »

Points above are correct. In an amp this old, dry/cold solder joints are quite common due to the age. Most often those will happen in the high currant carrying areas like the leads of power transistors, Emitter resistors that get heated up, power supply components etc., although it is also possible to see them in other areas of the boards also. Mostly due to heating and cooling over a number of years of use. Hot running Emitter resistor leads are mostly at fault.

Going back on my memory, I used to find faulty transistors by merely tapping on them like in the above post. Not that they had poor solder on the leads but internally they had faults. Those old transistors had weird things going on in them! Mostly when you hear odd, crackling noise that are intermittent.

Also check the small electrolytic caps C25/26/75 and 76. D5 and D7 are also culprits. Once I remember I had to replace a similar diode like the D7. After making sure there are no dry joints, if you do not have replacements in hand, try interchanging the transistors and diodes between the L and R channels and you should be able to find the culprit. Luckily, you have only a handful of transistors and diodes after the volume control.

Try not to adjust the idle currant pots if at all possible-unless you replace a transistor and you have the adjustment information.

Dan75 · « **Reply #33 on:** November 07, 2021, 07:05:50 pm »

Hi Andy,
I did not forget about this but I had other priorities that got first.
The caps C25, C26, C75 and C76 were soldered out of the board and checked using my MTester (Peak ESR meter like device).
The C75/C76 came up with an ESR of resp. 15 Ohms and 10 Ohms and a voltage loss of resp. 2,1 % and 1,9 %.

The caps C25/C26 came up with an ESR reading of resp. 5,4 Ohms and 6,1 Ohm, with a voltage loss of 1,1 % and 1,9%.
The C25 and C26 were changed out for new ones with the same specs but the other two were not changed out as I do not have them in stock.

Don't know if it is of any use to you. But I wonder if the ESR on the C75/76 is normal that high?

The transistors are swapped. I numbered them on the rail and on each of the transistors themselves. Then I made a swap as you suggested.
Took the transistors off the board using solder wick and soldering them back with fresh new solder

I regret that I did not first check the result after the recap and before the interchanged trans'.
Also did a visual check for dry soldering but couldn't find any yet. So maybe, when things start to fall back again, maybe a recap is in order.

I hooked the unit up now to some speakers and a CD player and will test it to see what happens.

Greetings,
Dan

andy3055 · « **Reply #34 on:** November 07, 2021, 08:35:01 pm »

Hi Dan,
As for the ESR of a cap, I believe there are charts you can refer to. Personally, I have never used an ESR checking device. At the time I did audio repairs, I used an analog meter to check the "kick" of an electrolytic, reversing the probes a few times. If a cap is leaky, the needle will start creeping back after the "kick," so to speak. I still use this method as I still do not own an ESR meter! I may decide to make one with all the schematics available freely these days.
Regards,
Andy

Dan75 · « **Reply #35 on:** November 07, 2021, 08:53:01 pm »

Hi Andy,

Well, I hooked the Pioneer up to my speakers and also connected a CD player and a turntable.
It looks the problem switched between channels. But what I also discovered is that the problem does not seem to exist in the AUX input but
distortion is very evident in Phono mode. It crackles, squeeks etc.

Maybe also in CD mode, but I have to test that some more to be sure.
I have an test record for audio equipment but it plays like sh*t. And just to be on the safe side, I also hooked the Pioneer up with a different
turntable, just to be sure the problem isn't within the TT. But no, it definitely is the amp.

But in Phono mode, it seems both channels are out of spec. In AUX mode (where my CD player is connected to) it seems fine now. Maybe I have to test it for a longer period of time.

andy3055 · « **Reply #36 on:** November 07, 2021, 09:07:40 pm »

The age of that amp is sort of a clue here. Those old amps had transistors that developed internal problems, if I remember correctly. Some people used a "freeze" can to find the culprits also. I think they are still available. On the other hand, you could probably apply heat. But how can you direct it to a narrow area? Bring the tip of the iron close to the transistor?

Just looked at the diagram and I am wondering if the Function selector is dirty, which is another common problem. For whatever it is worth, re-solder the leads of those transistors before that switch also.

Dan75 · « **Reply #37 on:** November 08, 2021, 11:05:54 am »

I will check the selector switch.
But that could not have caused a fuse to blow I guess.

Do you remember what you used to replace the transistors with back then? I want to order some parts for some other appliances soon and it would be nice if can order these as well.

Dan75 · « **Reply #38 on:** November 08, 2021, 12:40:40 pm »

By cleaning, do you mean all parts of the switch, as from face plate to on both print boards?

andy3055 · « **Reply #39 on:** November 08, 2021, 05:58:37 pm »

Did you say a fuse blew? I am sorry I did not notice that and that is not caused by the selector switch! My apologies. I was only thinking of weird noise that is intermittent. If you have to clean the switch, you will need to take it apart and from the looks of it, that is a bit of a process as it needs to come out of the board. It could be possible to take the metal cover off without taking the thing out of the board though.

Which transistors are you planning to replace? Before you buy them, interchange between the two channels to find out if one of them is really gone bonkers.

This is a good site to find equivalents for transistors in case you cannot get the original: https://alltransistors.com/transistor.php?transistor=13424

Dan75 · « **Reply #40 on:** November 08, 2021, 07:06:02 pm »

Yep, it was written in my very first post in this thread

To rewind: I sold a what I thought was a good solid amp to someone that initially did not seem to have the understandings of how to use audio and hook it up with other
components for example the speakers. I could tell, because I had to explain more than once how the speakers should be connected but he kept a look in his eyes that showed that he did not get it.
The Pioneer has 2 terminals on it, A and B.
So when it came back I was surprised that it had a defect because it was performing good when it left here.

Upon inspection I found that fuse 3 had blown and when I replaced it after visually checking the components and measuring the output, it fired right up.
That being said, that was when the amp started showing distortion and dropping on the same channel as the buyer reported as failed.
The channel has output but is distorted. But I think I have to make a longer test run in order to determine if it is only on the Phono stage and not the others like AUX, Tape etc.

And the interchange was already done as well

That was explained in my post yesterday. The output transistors I mean

There are no exact, same (or NOS) replacements for this amp anymore, only other transistors which come close but have other specs that will make your bias different and that is something beyond my understanding to adjust.

andy3055 · « **Reply #41 on:** November 09, 2021, 12:05:57 am »

Ah! I remember that. But then, after you replaced the fuses it started working but with this noise and the crackling, if I recollect. Am I correct? So, if that is the situation now, we can forget about the fuse issue and just look for the distortion and the noise. So, for that noise, it is quite possible the switch is dirty. But if there is distortion, that is something else like a bad transistor or a resistor for that matter.

By the way, if you have a can of switch cleaner, you can inject it in to the switch while operating it so that the crud will come off of the contacts.

Dan75 · « **Reply #42 on:** November 10, 2021, 02:36:46 pm »

Hi Andy,

I have cleaned switches and pots. I have a can of CRC cleaner that I use for this.

The next thing I did today was replace some caps that I have on hand. Going over the unit I saw something that did not notice earlier.
On a spot on the board that runs towards the selector switch.
I will look the numbers up in the service manual to tell you which ones.
It comprises of a transistor (D880 if I'm correct), a diode, and two resistors. This small section shows a blackened area that to me, seems to have been overheated at some point.
From the emitter of that transistor, a red wire runs directly to the selector switch (the Tape/Phono/AUX switch)
My best guess is, I haven't got around to check it yet, that one or more of these components are faulty.

I took a picture of the spot but in the photo the blackening is less prominent then with the naked eye.
Will post it next.

Dan75 · « **Reply #43 on:** November 10, 2021, 02:42:55 pm »

This is a close up of the spot:

Dan75 · « **Reply #44 on:** November 10, 2021, 02:54:05 pm »

It is transistor Q25, a 2SD880
and a 3,3 K Ohm resistor from what I can tell from the service manual, and another one
And lastly a diode D17 which should be MZ-192 ?? Think that are Pioneer part numbers.
[EDIT] that is not a Pioneer part number but seems to be the specific coding for a thermal fuse

Because something must have been causing that fuse number F3 to blow, that does not happen without a reason off course

andy3055 · « **Reply #45 on:** November 10, 2021, 05:59:12 pm »

That picture shows some sort of residue from a spill(?) like thing. There must be bad solder joints underneath. Clean and re-flow the solder in the vicinity and check the resistors for their correct values. MZ192 is a Zener diode with a voltage of 19.2 volts from what I can gather.

If you need to replace the 2SD880, I believe I have some of those which I can put in the mail. PM me of necessary.

Dan75 · « **Reply #46 on:** November 11, 2021, 09:37:45 am »

I will go through them soon. I already took the trans out and that one seems ok. Measures .460 and .457 over Base - Collector and Base - Emitter.
Other direction no reading.

Dan75 · « **Reply #47 on:** November 17, 2021, 08:24:52 pm »

Hi!
It took some time but I have checked the parts in the area I mentioned in my former post. The resistor R79 in the service manual shows that it should be a 3,3K (if that is not a fault in the manual!?)
but the one I took out measures 1577 Ohm on my meter.
The measurement complies with the color code on the actual resistor: Gold, Red, Green, Brown and not with what is says in the service manual: 3,3K ??

The diode (D17, which according to the SM is a MZ192) gave this measurement: Uf= 779mV C= 58pF

andy3055 · « **Reply #48 on:** November 18, 2021, 01:41:41 am »

R79: sometimes you do find discrepancies like that. As long as the resistor has the value according to the color bands, it should be ok unless someone before you had changed it.

Check R80 and R76. Also check the voltages in that part of the circuit. Q25 emitter and base. If that Zener diode is good, you should see the 19.2 volts on the base.

Dan75 · « **Reply #49 on:** November 18, 2021, 09:23:15 am »

I read your post just now, but I soldered the parts back in and wanted to check if it works, especially since you also wrote about cleaning the switches etc.
I did that, and after spraying them and turning the switches over for 50+ times, I also noticed they moved a whole lot smoother and easier.

This morning (different time zone off course) I hooked it up to the cd player and TT and all sounds good.
Don't know if those exist but I would like to have a test cd which one can use to test out audio equipment.
I have a record but that is only suitable for the phono input naturally as you cannot hook the TT up on a tape input, well maybe with a pre-amp?

The input selector switch runs from the face of the unit to one point on the PCB and to a second one via a sliding mechanism. I cleaned all three of these, as well
as all other switches and potentio meters on the unit.
Anyway, I don't know if it is still necessary to check the ones you pointed out, but as for now, it's working. No distorted sound on the phono either


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Author Topic: Asking for help on a blown channel on Pioneer SA-510 (Read 5958 times)

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