Vintage Pioneer SA-520 amplifier faulty display and aux-in

[Robee]

Hi guys.
I've found your interesting forum seeking for a problem similar to mine (here). Same amplifier but mine is working except for the fluorescent display and very low volume when I listen to something connected to Aux/Video input connector.
First of all I'm Roberto, writing from Italy, and congratulations to the guys who were able to fix it in the mentioned thread .
I've found the service manual on the web and I uploaded it here. I checked the tiny transformer connected to the display and it seems there's no continuity in the primay (2 pins) coil. Secondary is fine. I would like to take it apart and change it. I'm enough good with soldering iron. Though I'm unsure I would find a replacement and even if I found it I don't know how to get the proper voltages (by the way, the secondary coil has three pins).
I've read about the web there are companies where I might bring it and they would rebuild the wire coil but honestly it's getting quite hard to get a work done when it's matter of small things and small expense.
Is there a way to figure out the parametres of this transformer?
A smart guy found the ones of the main transformer here from the parametres of the two big capacitors on the mainboard but honestly I'm lost finding them that way for the small one.

Here is the photo of small transformer:

Here is the whole inner amplifier:

Thank you if you want to help!

 

[AsRock]

Maybe ? https://www.hifiengine.com/manual_library/pioneer/sa-520.shtml

 

[Robee]

Maybe ? https://www.hifiengine.com/manual_library/pioneer/sa-520.shtml

Hi AsRock, thank you. I have the the service manual. By the way, I can't sign in on HiFiEngine because it seems they locked new registrations from Europe.
In any case I'm not that good to get the voltages of the small transformer from the circuit manual :-/

 

[ArdWar]

Aahh, the joy of proprietary part numbers. It reveals nothing of value.....

I checked the tiny transformer connected to the display and it seems there's no continuity in the primay (2 pins) coil.

No continuity at all or just no beep? There should be 1.5k resistance if the main transformer secondary is good but display transformer primary is bad.

In any case I'm not that good to get the voltages of the small transformer from the circuit manual :-/

Measure VAC between the left pair of red and yellow cable on your first photo. Should be around 30V or something.

very low volume when I listen to something connected to Aux/Video input connector.

Does it only happen on Aux/Video input or is it also happen on Tape and Tuner inputs. All of those input should result in the same level when driven from the same source.

 

[Robee]

Aahh, the joy of proprietary part numbers. It reveals nothing of value.....


1. No continuity at all or just no beep? There should be 1.5k resistance if the main transformer secondary is good but display transformer primary is bad.


2. Measure VAC between the left pair of red and yellow cable on your first photo. Should be around 30V or something.


3. Does it only happen on Aux/Video input or is it also happen on Tape and Tuner inputs. All of those input should result in the same level when driven from the same source.

Thank you very much for finding the time to answer.

1. no beep. Waiting for a new multimetre because mine broke. I will check as soon as possible
2. I will
3. Tuner sounds fine to my ears. I didn't check tape but I will


I will get back as sooner as possible!

 

[Jacky_BEL]

Hello Roberto,

As mentioned in the service manual, there are 6 versions of SA-520.
See what model yours is, if HE or HB see if you can find the additional service manual ART-644.

The contents of the service manual has a electrical parts list, see if there is additional information about the transformer.

And for circuit description, try to get hold of the supplement of the service manual of SA-720 (ART-765).

As for low volume on aux/video , I would take a look at the switch assembly, try to clean the contacts if you can.

EDIT:

Do you get a voltage on the secondary of the small transformer? I believe it should be a very low AC voltage to heat the VFD filament.
It is such a simple circuit. I would be surprised if it is faulty.

I would concentrate on the other voltage needed to drive the VFD.

See if you can find Q23 and measure the voltages, they should be 34.5V and 18.8V.
It is in coordinates C3 on the schematic.

 

[Robee]

Hello Roberto,

As mentioned in the service manual, there are 6 versions of SA-520.
See what model yours is, if HE or HB see if you can find the additional service manual ART-644.

The contents of the service manual has a electrical parts list, see if there is additional information about the transformer.

And for circuit description, try to get hold of the supplement of the service manual of SA-720 (ART-765).

As for low volume on aux/video , I would take a look at the switch assembly, try to clean the contacts if you can.

EDIT:

Do you get a voltage on the secondary of the small transformer? I believe it should be a very low AC voltage to heat the VFD filament.
It is such a simple circuit. I would be surprised if it is faulty.

I would concentrate on the other voltage needed to drive the VFD.

View attachment 231673

See if you can find Q23 and measure the voltages, they should be 34.5V and 18.8V.
It is in coordinates C3 on the schematic.

Thank you Jacky_Bel. Lots of informations, great.
I have the schematics but I don't see any information about the main transformer. Mine should be model HE, since I am and I bought it in Europe when I was a kid. Actually yes, in the schematics the main transformer is AT-656 or something (too blurred) while mine is AT-705. I can't find the art-644 unfortunately.
I'm looking for a multimetre and will check everything. Thanks again

 

[Jacky_BEL]

Find more information on Pioneer SA-520:

ElektroTanya

And for the circuit description ART-765:

PIONEER SA420 SA520 SA620 SA720 CIRCUIT DESC

 

[Robee]

Thanks Jacky_Bel. Downloaded.
Guys sorry for disappearing. Lots of problems here with this pandemic crisis... Though, being back means I didn't get an electric shock!!!

Aahh, the joy of proprietary part numbers. It reveals nothing of value.....


No continuity at all or just no beep? There should be 1.5k resistance if the main transformer secondary is good but display transformer primary is bad.


Measure VAC between the left pair of red and yellow cable on your first photo. Should be around 30V or something.


Does it only happen on Aux/Video input or is it also happen on Tape and Tuner inputs. All of those input should result in the same level when driven from the same source.

I have another multimeter now and actually you were right: no beep but, if I'm doing things right, there is VAC at the leads of the small transformer. At the secondary I measure 3,35 V.
Between the yellow and red cables you said, I measure 1,68 V.

Hello Roberto,

As mentioned in the service manual, there are 6 versions of SA-520.
See what model yours is, if HE or HB see if you can find the additional service manual ART-644.

The contents of the service manual has a electrical parts list, see if there is additional information about the transformer.

And for circuit description, try to get hold of the supplement of the service manual of SA-720 (ART-765).

As for low volume on aux/video , I would take a look at the switch assembly, try to clean the contacts if you can.

EDIT:

Do you get a voltage on the secondary of the small transformer? I believe it should be a very low AC voltage to heat the VFD filament.
It is such a simple circuit. I would be surprised if it is faulty.

I would concentrate on the other voltage needed to drive the VFD.

View attachment 231673

See if you can find Q23 and measure the voltages, they should be 34.5V and 18.8V.
It is in coordinates C3 on the schematic.

As you maybe read above, I measure 3,35 V on the secondary. If I found the right Q23 transistor (I think so) I measure 11V at the edmitter and 9,8V at the base. I checked on the web and it's a Panasonic C1384. There are more on the mainboard but I didn't take it apart, yet, to check accurately. The transistor I checked is this, near the transformer:

I was forgetting: when I took the above measures, the multimeter slowly switched continously from 0 to those values. It was not a stable value.

Guys, I think I found the culprit. @Jacky_BEL maybe you were right: I've found a loose transistor near the VFD. Probably it has desoldered. I will take it apart now and test it.
You can see it in the photos

Checking the transistor after taking it apart, it seems ok (done this way). Do you think changing it with a new one would though be better?
Another doubt I have: what should the size of the tin wire be? I have a 30W fixed temperature and tip soldering iron. Am I going to do damages? I'm ready to buy what needed

 

[Jacky_BEL]

Do you mean diameter of soldering tin? I would say something like 1 mm.

 

[Robee]

Do you mean diameter of soldering tin? I would say something like 1 mm.

Yes that's what I meant. I have such diameter and new adjustable soldering stuff has arrived.
The only concern is the old transistor leads are now cut. Then I would have less room for soldering. Probably I'll buy a new transistor

 

[Wirko]

Hi Roberto,

the loose transistor that you've found is probably Q23. It's close to the VFD and it's surrounded by components that look like R108 (larger resistor, looks damaged), R97 (smaller resistor, red-red-red-gold = 2.2k) and D14 (19.2V zener diode, the PCB next to it looks burned). Do you have easy to the PCB access from below? If you can, inspect all these components and the PCB around them from above and below to see which ones have been overheating - that's revealed by the dark brown colour of the PCB. Do any of them get hot in operation (caution, might be very hot)? Have any PCB tracks come off the board due to the heat? Also try to follow the PCB tracks and compare them to the schematic so maybe you can confirm that it is (or isn't) Q23.

If you can measure and report the voltages at all three terminals of the Q23, it would give us enough information to tell which components are to be suspected. The voltages at C and E should be close to those in the schematic, and the voltage at B should be about 0.7 V above E. Now if it turns out Q23 is bad, you can swap it with many other types that are easily available, you just need to pay attention to power rating - must be at least 1 W.

It may also be VFD driver ICs that have failed of course, which would be a bit harder to determine.

 

[Robee]

Hi Wirko. Thanks for helping.
I didn't notice the PCB and components had overheated. I will take a closer look as soon as I'll be home. Yes I can easily access it from below.
Yes you are right. It is the Q23 that @Jacky_BEL pointed me to. But I'm not much into all this and I didn't find it until i touched it and realised it was not soldered. I think i detached it years ago while doing a dust cleanup.
Even without desoldering the components you said, I tested the diode and it looked working.
I will post closer photos.

Edit: I already took the transistor apart. That's why the measures wouldn't make sense. Should I take the resistances and diode apart as well to check them? I measured them onboard and values don't make sense in comparison with the ones you said. The Zener diode gives me a low, stable voltage with probes in a certain direction and a little, bigger voltage (which slowly increases) inverting the probes.

I also looked better: actually, looking from below, there's some sign of overheating Oh no! :'(

 

[Jacky_BEL]

The zenerdiode voltage of 19.2V means that you can not really test it with a common multimeter.
But the results as you describe them seem to indicate that the zenerdiode is OK.
Only way to really test it is to power on the circuit and measure the voltage directly across the zenerdiode.
(But you know , be carefull when doing so)

The "big" resistor is likely the 1/2 W resistor, and meant to dissipate power so it can get a little bit hot and give some discoloration over time to the PCB.

 

[Wirko]

I see now, these are normal signs of heating but not overheating. However, without the transistor in its place, the zener diode voltage should be around 19.2V, stable. It's actually the best method to test it as you have excluded the possibly faulty transistor and all the components that are powered by the 18.8V line.

Don't desolder the resistors and diode just yet but do refresh their solder joints by heating them up and adding a little solder. Cold joints are all too common in old electronics. Then measure the voltages at R108, R97, D14 again.

The PCB tracks don't seem damaged but it's still a good idea to check them carefully. Shine a powerful torch or another light through the PCB, from the component side - it can reveal cracked/broken tracks that you wouldn't otherwise see.

 

[Robee]

The zenerdiode voltage of 19.2V means that you can not really test it with a common multimeter.
But the results as you describe them seem to indicate that the zenerdiode is OK.
Only way to really test it is to power on the circuit and measure the voltage directly across the zenerdiode.
(But you know , be carefull when doing so)

The "big" resistor is likely the 1/2 W resistor, and meant to dissipate power so it can get a little bit hot and give some discoloration over time to the PCB.

Sorry I don't understand. Can I test it or not? Where does 19.2 V come from?

I see now, these are normal signs of heating but not overheating. However, without the transistor in its place, the zener diode voltage should be around 19.2V, stable. It's actually the best method to test it as you have excluded the possibly faulty transistor and all the components that are powered by the 18.8V line.

Don't desolder the resistors and diode just yet but do refresh their solder joints by heating them up and adding a little solder. Cold joints are all too common in old electronics. Then measure the voltages at R108, R97, D14 again.

The PCB tracks don't seem damaged but it's still a good idea to check them carefully. Shine a powerful torch or another light through the PCB, from the component side - it can reveal cracked/broken tracks that you wouldn't otherwise see.

Ok. I will do so and let you know. Thanks again

 

[Jacky_BEL]

Sorry I don't understand. I can't test it or not? Where does 19.2 V come from?

You can try to measure the voltage across the zenerdiode with the amplifier turned on, it should measure 19.2V
When you try to do a diodetest (on the switched off amplifier !) with a battery-powered multimeter (usually 9V battery) , it can not test a 19.2V zenerdiode.
In the other direction the zenerdiode will just work as a diode and will indicate a voltage of 0,5V to 0,7V

19.2V is the caracteristic of the zenerdiode D14 MZ-192.
From the parts list you find MZ-192 is actually a WZ-192 zenerdiode.
From the datasheet of WZ-192 you find the zener voltage is 19.2V

 

[Robee]

I'm learning lots of things. Thank you!!!

 

[Wirko]

Careful, you marked the position of the diode and one resistor wrong. Here's where they actually sit:

 

[Robee]

Careful, you marked the position of the diode and one resistor wrong. Here's where they actually sit:
View attachment 237371

Oh! Thanks. I should have seen the short circuit. You lucky guys don't need me to fix your appliances!

Ok I finally measured them with amplifier on, before going ahead: big resistance is R98 because I get 817 Ohm. Small resistance is R97 because I get 2,2 KOhm.
The diode gives me:
1. in diode test mode: 0,70 V and 2,5 V depending on the polarity of probes;
2. voltage mode: 0V or 7 V depending on the polarity of probes

 

[Wirko]

Oh! Thanks. I should have seen the short circuit. You lucky guys don't need me to fix your appliances!

Ok I finally measured them with amplifier on, before going ahead: big resistance is R98 bceause I get 817 Ohm. Small resistance is R97 because I get 2,2 KOhm.
The diode gives me:
1. in diode test mode: 0,70 V and 2,5 V depending on the polarity of probes;
2. voltage mode: 0V or 7 V depending on the polarity of probes

When the amplifier is on, measure the voltages only, nothing else. Don't use the ohmmeter or the diode testing function. You won't get any meaningful results because the ohmmeter generates its own small voltage for testing, and any other voltage/current present in the circuit interferes with it. There is also a slight chance the instrument gets damaged (although we're dealing with less than 40 volts here, and multimeters have some overvoltage protection).

0 V or 7 V, that's strange. If you get 7 V and then swap the probes, you must get -7 V. Try it with a battery or any source of DC voltage, it must behave exactly like that. Looking at your last pic that shows the components, (+) is on the left side of the diode and is marked by a big green dot on the PCB. (-) is on the right side.

7 volts is also far too little. It should be close to 19.2 V. But to track down what's wrong you also need to find R108, which may not be easy at all. Then measure the DC voltages:
- from both ends of R108 to ground; one should be 37V, the other 34.5 V
- from both ends of R97 to ground; one should be 34.5 V (same as above), the other 19.2 V (same as the voltage on zener diode).

What kind of multimeter do you have?

 

[Jacky_BEL]

My guess is that R108 is one of the resistors that is mounted somewhat higher off the PCB , with yellow violet black color code band markings.
Maybe you can follow the traces printed on the PCB and see if the component number is marked on the PCB.

 

[Robee]

When the amplifier is on, measure the voltages only, nothing else. Don't use the ohmmeter or the diode testing function. You won't get any meaningful results because the ohmmeter generates its own small voltage for testing, and any other voltage/current present in the circuit interferes with it. There is also a slight chance the instrument gets damaged (although we're dealing with less than 40 volts here, and multimeters have some overvoltage protection).

0 V or 7 V, that's strange. If you get 7 V and then swap the probes, you must get -7 V. Try it with a battery or any source of DC voltage, it must behave exactly like that. Looking at your last pic that shows the components, (+) is on the left side of the diode and is marked by a big green dot on the PCB. (-) is on the right side.

7 volts is also far too little. It should be close to 19.2 V. But to track down what's wrong you also need to find R108, which may not be easy at all. Then measure the DC voltages:
- from both ends of R108 to ground; one should be 37V, the other 34.5 V
- from both ends of R97 to ground; one should be 34.5 V (same as above), the other 19.2 V (same as the voltage on zener diode).

What kind of multimeter do you have?

I'm doing lots of wrong things, it seems. Thanks for your patience.
I will check again the voltage of the diode. I did the battery test but that's DC. Honestly I don't know wehere on the amplifier board I have DC... Ok, I will do as you say.
My multimeter is an Aneng AN8008: https://needful.co.ua/image/catalog/product/an8008/AN8008-Eng.pdf

My guess is that R108 is one of the resistors that is mounted somewhat higher off the PCB , with yellow violet black color code band markings.
Maybe you can follow the traces printed on the PCB and see if the component number is marked on the PCB.

Doing something else now. I'll check soon

 

[Wirko]

Power supply voltages for transistors and integrated circuits are always DC. Your amplifier would happily run on batteries (you'd need many) with some modifications.

 

[Robee]

When the amplifier is on, measure the voltages only, nothing else. Don't use the ohmmeter or the diode testing function. You won't get any meaningful results because the ohmmeter generates its own small voltage for testing, and any other voltage/current present in the circuit interferes with it. There is also a slight chance the instrument gets damaged (although we're dealing with less than 40 volts here, and multimeters have some overvoltage protection).

0 V or 7 V, that's strange. If you get 7 V and then swap the probes, you must get -7 V. Try it with a battery or any source of DC voltage, it must behave exactly like that. Looking at your last pic that shows the components, (+) is on the left side of the diode and is marked by a big green dot on the PCB. (-) is on the right side.

7 volts is also far too little. It should be close to 19.2 V. But to track down what's wrong you also need to find R108, which may not be easy at all. Then measure the DC voltages:
- from both ends of R108 to ground; one should be 37V, the other 34.5 V
- from both ends of R97 to ground; one should be 34.5 V (same as above), the other 19.2 V (same as the voltage on zener diode).

What kind of multimeter do you have?

Ok, I've found R108 and it was close to the small transformer (see photo).
R108: one side 40,2 V and the other end 38,5 V;
R97: one side 38,4 V and the other one 19,6 V