I have a vintage Pioneer SA-608.
When I first turned it on, the indicator panel didn’t work and I heard the relay (also DC protection according to Service Manual?) tripped on and off.
Also one of both fuses at the primary side of the transformer was blown.
There was an oil like substance around the power supply capacitors, and indeed, one of them had only half the capacitance it should have had.
So I replaced them.
When I turn it on know, I here the relay click, but the indicator panel doesn’t come on at first. After a while suddenly the relay trips again and then the indicator panel works.
I’m starting to think about an intermittent transistor at the power supply, one that works when it’s hot, but not when it’s cold.
I checked the output transistors with the diode test and measured the ohms. Everythings seems fine. I don’t have a scope, otherwise I would have checked it already. I’m contacting a buddy of mine the help me out, but in corona times it’s not so easy to meet and test gear.
So I was hoping that the knowledge of the many experienced guys here on the forum would give me a direction for where to search.
The schematics are avaiable on Hifiengine. I already read the threads on the forum that include my amplifier and similar ones. I even found a suggestion that the second fuse is not necessary, it’s for the 240V line?
Many questions but no solutions. What are your insights?
Thank you in advance!
When I first turned it on, the indicator panel didn’t work and I heard the relay (also DC protection according to Service Manual?) tripped on and off.
Also one of both fuses at the primary side of the transformer was blown.
There was an oil like substance around the power supply capacitors, and indeed, one of them had only half the capacitance it should have had.
So I replaced them.
When I turn it on know, I here the relay click, but the indicator panel doesn’t come on at first. After a while suddenly the relay trips again and then the indicator panel works.
I’m starting to think about an intermittent transistor at the power supply, one that works when it’s hot, but not when it’s cold.
I checked the output transistors with the diode test and measured the ohms. Everythings seems fine. I don’t have a scope, otherwise I would have checked it already. I’m contacting a buddy of mine the help me out, but in corona times it’s not so easy to meet and test gear.
So I was hoping that the knowledge of the many experienced guys here on the forum would give me a direction for where to search.
The schematics are avaiable on Hifiengine. I already read the threads on the forum that include my amplifier and similar ones. I even found a suggestion that the second fuse is not necessary, it’s for the 240V line?
Many questions but no solutions. What are your insights?
Thank you in advance!
You begin by checking that all rails are correct. These are the -/+40 volt unstabilised lines and the -/+20 volt stabilised rails.
Also check the 27 and 13.6 volt points around Q21
If those are correct then you next confirm that the DC offset for each channel (as measured before the speaker relay) is close to zero volts DC.
If caps have leaked then its possible there is conductive/corrosive substance on the PCB and that can cause problems.
Also check the 27 and 13.6 volt points around Q21
If those are correct then you next confirm that the DC offset for each channel (as measured before the speaker relay) is close to zero volts DC.
If caps have leaked then its possible there is conductive/corrosive substance on the PCB and that can cause problems.
Thank you for your answer.
The rail voltages are ok, but the 20V rail voltages I can’t find.
Where is there a 20V rail on the schematic?
The voltages around Q21 are 13,8 V and 28,8 V, so ok.
The DC offset is 37mV between all speaker terminals.
I noticed that the 20,4V point at Q19 drops regulary, with the effect of the relay engaging or disengaging. Is this normal? Or is there something wrong about the zenerdiode D8 or capacitor C239?
The rail voltages are ok, but the 20V rail voltages I can’t find.
Where is there a 20V rail on the schematic?
The voltages around Q21 are 13,8 V and 28,8 V, so ok.
The DC offset is 37mV between all speaker terminals.
I noticed that the 20,4V point at Q19 drops regulary, with the effect of the relay engaging or disengaging. Is this normal? Or is there something wrong about the zenerdiode D8 or capacitor C239?
Just letting know that the amplifier plays music for the moment. When it’s on for a while everything seems to work fine. So I suppose a intermittent transistor in the psu?
Well Q19 is the positive 20 volt regulator and so if the emitter volts is dropping out then that suggests a problem.
Have you checked for any poor joints around the transistor?
Either the transistor or Zener could be faulty. If the voltage across the Zener remains correct while the emitter volts drops then the transistor is suspect.
If the Zener voltage falls as well then it could be either part at fault. The transistor is not critical, any suitably sized NPN device should work OK. Something like a TIP41C
Also check for dries on those resistors feeding the transistor.
Have you checked for any poor joints around the transistor?
Either the transistor or Zener could be faulty. If the voltage across the Zener remains correct while the emitter volts drops then the transistor is suspect.
If the Zener voltage falls as well then it could be either part at fault. The transistor is not critical, any suitably sized NPN device should work OK. Something like a TIP41C
Also check for dries on those resistors feeding the transistor.
Attachments
I checked the things you said. No poor joints as far as I can tell.
The voltage drop does not happen on the zener.
So we found the culprit! Voltage regulator Q19!
I’m very happy and I learned again something new.
I will replace the zener as well as the transistor. For such low cost components it’s not worth thinking over.
Should I replace the negative 20V regulator also? Or not?
Finding a replacement transistor is not the problem, it’s finding one that is common around here.
Thank you very much, you really helped me out!
The voltage drop does not happen on the zener.
So we found the culprit! Voltage regulator Q19!
I’m very happy and I learned again something new.
I will replace the zener as well as the transistor. For such low cost components it’s not worth thinking over.
Should I replace the negative 20V regulator also? Or not?
Finding a replacement transistor is not the problem, it’s finding one that is common around here.
Thank you very much, you really helped me out!
Extra question:
In finding a replacement, what are the critical qualities?
Is the ‘current transfer hFE’ of importance for example?
In finding a replacement, what are the critical qualities?
Is the ‘current transfer hFE’ of importance for example?
That all sounds promising 🙂 I'm assuming the collector volts is staying at around the 36 volts or so, in other words the incoming voltage is holding up OK.
It probably is, but worth just mentioning... in fact it almost certainly is because if it were not then the Zener voltage would fall as well.
Transistors are relatively non critical here. Voltage rating, current and power handling are what matters and the TIP41C (and TIP42C for the negative PNP one) should be universally available but buy from reputable sources. hFE doesn't matter so much either as most common devices will have plenty of current gain.
(It is not like selecting devices to give the highest open loop gain of a front end of an amplifier where it can and does matter)
So TIP41B or C and TIP42B or C are fine as are TIP31B or C and TIP32B or C.
It probably is, but worth just mentioning... in fact it almost certainly is because if it were not then the Zener voltage would fall as well.
Transistors are relatively non critical here. Voltage rating, current and power handling are what matters and the TIP41C (and TIP42C for the negative PNP one) should be universally available but buy from reputable sources. hFE doesn't matter so much either as most common devices will have plenty of current gain.
(It is not like selecting devices to give the highest open loop gain of a front end of an amplifier where it can and does matter)
So TIP41B or C and TIP42B or C are fine as are TIP31B or C and TIP32B or C.
Very well, thank you for your excellent information.
When the components are replaced, I will give you a heads up if the problem is definitively solved.
I can take a few days/weeks because many shops are closed here due to corona.
Soon we will know! Thanks and see you soon
When the components are replaced, I will give you a heads up if the problem is definitively solved.
I can take a few days/weeks because many shops are closed here due to corona.
Soon we will know! Thanks and see you soon
You're welcome 🙂
...and remember that many other transistor types would be suitable. If you have any lying around or perhaps in some old scrap equipment then look them up. If the Zener keeps its voltage then it is going to be OK:
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
...and remember that many other transistor types would be suitable. If you have any lying around or perhaps in some old scrap equipment then look them up. If the Zener keeps its voltage then it is going to be OK:
Datasheet catalog for integrated circuits, diodes, triacs, and other semiconductors, view
The amplifier is fixed!
I had a MJE15032G lying around from my Honey Badger Build.
When I had pulled out the broken transistor I turned the amplifier on and indeed, I got exactly the same issues I experienced before. So this was the problem for sure.
Again thank you very much!
Up to the next one 🙂
I had a MJE15032G lying around from my Honey Badger Build.
When I had pulled out the broken transistor I turned the amplifier on and indeed, I got exactly the same issues I experienced before. So this was the problem for sure.
Again thank you very much!
Up to the next one 🙂
excellent news.