Hello, everybody, I have a question for you, I appreciate your help greatly.
There is a click sound a few mintes after turning on, at the same time speakers stop working for very short time, less than 1 second. Then it still works well without any problem.
Each turning on the amp, it only happens one time.
I wonder if it is BIAS and DC Offset issues?
How to deal with it? I mean how to adjust them. I found out the manual, but nothing helps.
Thank you for your time and instruction.
There is a click sound a few mintes after turning on, at the same time speakers stop working for very short time, less than 1 second. Then it still works well without any problem.
Each turning on the amp, it only happens one time.
I wonder if it is BIAS and DC Offset issues?
How to deal with it? I mean how to adjust them. I found out the manual, but nothing helps.
Thank you for your time and instruction.
Pioneer SA-8500 - Manual - Stereo Integrated Amplifier - HiFi Engine
This amp is quite old, has it had a service such as replacing the electrolytic caps previously? It has a speaker relays fitted, so if that clicks when the sound cuts out as you describe, the protection circuit is doing what it should when a DC fault or overload is detected at the output.
Initally, disconnect any input signal and the speakers, turn down volume and recheck the time it takes trip now, with no power output. Also measure any, even a small DC offset voltage between the output terminals of either channel. There will a very small offset anyway but < 50mV for an old amp is of no concern. A more significant voltage may only occur as a quick spike when the relay cuts out so you should actually measure the voltage before the relay if you want to see what happens with it after that second, on your meter. The output coil or connection point 17 on either amplifier assembly, would be a suitable point to measure but take care not to slip with meter probes - almost guaranteed to cause a short that kills your amp.
So use leads with Ez hooks, IC clips etc. if you can.
If it takes a few minutes after power-up for the fault to occur, then this is also a thermal issue and could be elusive if it's not just down to leaky old caps in the protection circuit (and elsewhere). As the amp works otherwise, it can't be a serious matter but the cost of total recapping, if needed, might cause wallet pain.
This amp is quite old, has it had a service such as replacing the electrolytic caps previously? It has a speaker relays fitted, so if that clicks when the sound cuts out as you describe, the protection circuit is doing what it should when a DC fault or overload is detected at the output.
Initally, disconnect any input signal and the speakers, turn down volume and recheck the time it takes trip now, with no power output. Also measure any, even a small DC offset voltage between the output terminals of either channel. There will a very small offset anyway but < 50mV for an old amp is of no concern. A more significant voltage may only occur as a quick spike when the relay cuts out so you should actually measure the voltage before the relay if you want to see what happens with it after that second, on your meter. The output coil or connection point 17 on either amplifier assembly, would be a suitable point to measure but take care not to slip with meter probes - almost guaranteed to cause a short that kills your amp.
So use leads with Ez hooks, IC clips etc. if you can.If it takes a few minutes after power-up for the fault to occur, then this is also a thermal issue and could be elusive if it's not just down to leaky old caps in the protection circuit (and elsewhere). As the amp works otherwise, it can't be a serious matter but the cost of total recapping, if needed, might cause wallet pain.
I measured the speaker output voltage for a few times accordingly, to my surprise they are very good, right side is 2mv, left side -2mv. And, if there is no connections, disconnected any inputs and outputs, I observed, there seemed no that unnecessary click.
The amp was working properly one week ago, and I can't see anything wrong inside, clean and like new. wondering why this short protection comes from?
Thank you very much.
Apologies for posting the wrong manual, above. The detail and explanations of how the protection system works (see the manual listed as MkII additional) should be easier to follow now: Pioneer SA-9500 - Manual - Stereo Integrated Amplifier - HiFi Engine
So the first question again, has the amplifier had a re-cap? The caps will have different date codes and probably come from several manufacturers if they have been replaced. Their date codes, if any, will be much later, of course. Protection systems are notorious for false triggering when electrolytics begin to fail, so we look for intermittent problems where they may be anticipated, in consumables like electrolytic caps and where heat is generated.
When the inputs and load are removed, the fault doesn't occur, right? Well, let's see which is the culprit. I suspect the speaker connection because it provides a load and thus a current that can be sensed by the circuit. Reconnect the speakers only, and see if the triggering returns. If the fault also requires the signal input to be connected, then it still points to erratic protection circuit operation. Don't forget that a speaker fault can also produce a DC overload - swap them to check.
Regarding the DC measurements, I was asking you to look for a spike in the DC at the time when the relay trips. An oscilloscope would show this but an analog meter should also flicker at least if not remain high for the short period. With a DMM, you may not be able to measure such a brief event, but there should be some indication.
So the first question again, has the amplifier had a re-cap? The caps will have different date codes and probably come from several manufacturers if they have been replaced. Their date codes, if any, will be much later, of course. Protection systems are notorious for false triggering when electrolytics begin to fail, so we look for intermittent problems where they may be anticipated, in consumables like electrolytic caps and where heat is generated.
When the inputs and load are removed, the fault doesn't occur, right? Well, let's see which is the culprit. I suspect the speaker connection because it provides a load and thus a current that can be sensed by the circuit. Reconnect the speakers only, and see if the triggering returns. If the fault also requires the signal input to be connected, then it still points to erratic protection circuit operation. Don't forget that a speaker fault can also produce a DC overload - swap them to check.
Regarding the DC measurements, I was asking you to look for a spike in the DC at the time when the relay trips. An oscilloscope would show this but an analog meter should also flicker at least if not remain high for the short period. With a DMM, you may not be able to measure such a brief event, but there should be some indication.
I got this manual, thanks, Ian.
The problem seems worse and worse, Yesterdya the unexpected relay noise happened only once after turning on for a while, but today the relay clicks more than one ( two, or three and more ) time.
Plus, Previously I said there was no click sound after I unplugged all cables ( maybe I just didn't notice that ), but today I heard clearly the relay kicks in and out inside the box.
As for the re-cap, I compared it to the online images, all components of mine look original. Not sure if the first owner rebuilt it or not, mostly likely not.
Here is the adjustment instruction on the manual, it needs some resistors to do that, is there another way to do the adjustment? In fact what I measured is wrong.
9. ADJUSTMENT
The SA-9500 ll amplifier employs the same type
of power amplifier assembly in both left and right
channels. Any adjustment will thus have to be
identica.li n both channels,a nd is limited to adjustments
of the idler current.
1. Disconnect the jumper plugs, and terminate the
POWER IN terminals with a 5.1k(2 resistoru.
2. Connect 8Sl resistors to the SPEAKERS A
terminals, and set the SPEAKERS switch to A.
3. Turn VR, in fully a counter-clockwise.
4. Tum the POWER switch ON, and then readjust
VR, so that the voltage between terminals
No. 3 (+) and No. 9 ( ) reads 30mV.
5. Now check that the voltage belween terminals
No. 6 (+) and No. 12 ( ) reads 30mV t10mV
(in order to check the current distribution,
sincet he final stagesa re in parallel) .
6. Leave the amplifier ON for about 30 minutes,
then repeat steps 4 and 5.
7. Finally, apply an actual signal, and check for
no crossoverd istortion.
Thank you very much.
Don't try to adjust the protection thresholds. Not only is this inviting trouble now and for correct settings later, I see no reason to assume that adjusting the current protection limits will solve the problem. You have an intermittent fault, not a stable one and you can't sensibly adjust something unless it has a steady state of operation for reference.
If a problem is worsening, then something is progressively changing over time and temperature (as the amps warm up) and capacitors (as the electrolyte slowly evaporates or degrades) are the main suspects. I suggest you look into recapping - at least for the few small values in the protection circuits and decoupling caps in the power amplifiers. The main power supply smoothing caps may be expensive but the amplifier will show an improvement when they are replaced - even with standard grade caps. Approaching 40 years, those caps may still work but few will have anywhere near a low enough ESR.
Take a close look around the power amplifier for signs of overheating, then check that the thermal grease around the output stage is still flexible and keeping the power transistors cool. Look closely for even small signs of overheated components and check that all the voltages shown for the power amp boards roughly match those you measure on the power amplifiers. Note any unsteady measurements or those that spike occasionally as mentioned before. You didn't comment on this so I assume you haven't seen any spiking or unsteadiness in the DC voltage at the coils or relay input terminals. Recheck the marked voltages after recapping and compare. Again, any voltages measurements should be made with the speakers etc. disconnected.
Logically, if the amplifier outputs are the relay's sense point and yet you can't measure any fault like voltage spiking or unsteadiness on either output when the relay operates, then the protection circuit must be making its own faults! I have my doubts about that but new caps should at least ensure stability.
If a problem is worsening, then something is progressively changing over time and temperature (as the amps warm up) and capacitors (as the electrolyte slowly evaporates or degrades) are the main suspects. I suggest you look into recapping - at least for the few small values in the protection circuits and decoupling caps in the power amplifiers. The main power supply smoothing caps may be expensive but the amplifier will show an improvement when they are replaced - even with standard grade caps. Approaching 40 years, those caps may still work but few will have anywhere near a low enough ESR.
Take a close look around the power amplifier for signs of overheating, then check that the thermal grease around the output stage is still flexible and keeping the power transistors cool. Look closely for even small signs of overheated components and check that all the voltages shown for the power amp boards roughly match those you measure on the power amplifiers. Note any unsteady measurements or those that spike occasionally as mentioned before. You didn't comment on this so I assume you haven't seen any spiking or unsteadiness in the DC voltage at the coils or relay input terminals. Recheck the marked voltages after recapping and compare. Again, any voltages measurements should be made with the speakers etc. disconnected.
Logically, if the amplifier outputs are the relay's sense point and yet you can't measure any fault like voltage spiking or unsteadiness on either output when the relay operates, then the protection circuit must be making its own faults! I have my doubts about that but new caps should at least ensure stability.
Check the soldering of any component that is attached to a heat sink. The heatsinks do not move with the movement caused by temperature changes at the same rate as the components and this causes dry joints.
Thanks.
It's out of my knowledge, will keep observing it (room temperture changes now in Canada, is it the cause? ), maybe have it repaired somewhere later. I haven't locally found out a real service guy who is able to deal with audio unit properly. A Few months ago, a guy who claimed he had 25 or 30 year experience about audio repair, I sent my high end yamaha vintage to him, only one minute, I myself saw he almost ruined my amp with a serious short , then he blamed me that I didn't tell him the issue exactly...🙁
Then I sent this yamaha to another guy, yes, he made it after 40 days, he messed it up inside out, missing lots of bolts and screws, some inside components even hanging in the air, scrathed the box and face awfully, and charged me a big money. When I got it home, and sold out cheap.
Frankly I trust forum members here much more than those so-called service persons.
I have another 9500, not this model II, working very nice like this one ever worked. Hope it lasts for ever. it is a pain to keep old audio stuff.
Thank you very much. 🙂
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Ian, today I measured the bias DC offset again, disconnected all ins and outs, volume down to zero, and unplugged the jumpers... ( took the easier measurement that I got online)
____________________________________________________
4. Tum the POWER switch ON, and then readjust
VR, so that the voltage between terminals
No. 3 (+) and No. 9 ( ) reads 30mV.
5. Now check that the voltage belween terminals
No. 6 (+) and No. 12 ( ) reads 30mV t10mV
_____________________________________________________
Right side channel is good, it was adjusted to 30mv between No.3 / No.9, Then 32mv between No.6 / No.12. Looks perfect.
But, the left side, if I adjust the voltage to 30mv between 3 and 9, the voltage goes up to 90mv between 6 and 12 ( should be 30 +/-10 mv ), a big difference. Tried several times, two voltages didn't get close at all.
After playing for some time, I can feel the left side is warmer than the right.
I could not get left side VR back to the previous position, so just left the voltage ( between 3 and 9 ) to 25mv, rather than 30mv, the voltage between 6 and12 now remains 80mv something.
I can't hear anything wrong, sounds good. and can't hear the relay clicks anymore for now, for sure I will keep watching.
This is what I did today, do you have any idea about that?
Many thanks.
Kuer
There is not going to be any magic fix or fast food solution on your problem on the other hand you may have a few facts offered and then decide ....
Fact 1
All Pioneer SA-9500II with no exceptions at this age will suffer from capacitor issues ...By the way you may look at them as long as you like and expect them to talk to you, to tell you that ESR is now sky rocket high But we both know that this is not going to happen ...The only way is to sample a few measure for capacitance and ESR see that there is trouble and decide to replace them all in order to keep the amp working for many years to come .
Fact 2
All Pioneer SA-9500II with no exceptions at this age are equipped with notorious failing NEC semiconductors ...NEC transistors have excellent audio performance even better at some points from the Toshiba's commonly used in most Japanese amps BUT they DO fail if manage to come up at this age after all.
The type of failure is specific and your are not looking for a transistor that is shorted but a transistor that goes shorted or open Only if powered So this is not going to be easy to trace .
Fact 3
All Pioneer SA-9500II with no exceptions at this age will suffer from some contact or soldering issue ...so inspection for that is in order ( luckily this has not much to do with your problem ) this is a general service advice ( there is a remote possibility very rear in your case that you have soldering issues in the protection area )
Fact 4
All Pioneer SA-9500II with no exceptions at this age will suffer from some cleaning issue scratchy pots and switches also have nothing to do with the problem specified this is also a general service advice .
In reality
A) you need to trace if your problem lays on the amplifier that triggers the protection or the protection is at fault and auto triggers without amplifier problem .
B) To do that you need to observe offset before the relay ( before the protection ) at the time of the fault.
If offset remains low as checked before and in general anything less than 50mv but still protection is activated then the problem lays on the protection circuit .
C) if the offset is increased ( that can be any thing above 300mv (threshold point of protection ) up to full rail voltage when at fault , and protection is activated , measuring before the relay and before the protection Then the amp is at fault ....
Even more specifically:
---In case the protection is at fault suspects are in the specific order :
Q7, Q15, Q6 ,Q15,C13, C14, The protection circuit will also need a power supply to operate .You have a very detailed service manual observe and verify all voltage present according to the service manual if something is wrong there at the time of fault we will have to check the power supply that feeds the protection .
---In case the amplifier is at fault
The first thing you will have to look is the drivers of both amplifiers ...specific driver of NEC has a history of failure as described above.
---Finally this amplifier has separated power supply for the first stages of the amplifier From statistic point of view there have been reports for problems, there any loss of voltage there related to either soldering or capacitor issue will result activation of the protection ... ( area of Q8,9 )
The only possible way to trace a NEC transistor at fault IE during working and powered is a heat gun and a freeze spray ...If transistor in protection is at fault freezing it with a spray will momentary make it work and point you the problem Alike this can be done in the drivers and any other transistor that presents periodic failure ....Heat or cold will make it behave different and point you the problem ...A solution that works most of the times .
That's about it ...
There is not going to be any magic fix or fast food solution on your problem on the other hand you may have a few facts offered and then decide ....
Fact 1
All Pioneer SA-9500II with no exceptions at this age will suffer from capacitor issues ...By the way you may look at them as long as you like and expect them to talk to you, to tell you that ESR is now sky rocket high But we both know that this is not going to happen ...The only way is to sample a few measure for capacitance and ESR see that there is trouble and decide to replace them all in order to keep the amp working for many years to come .
Fact 2
All Pioneer SA-9500II with no exceptions at this age are equipped with notorious failing NEC semiconductors ...NEC transistors have excellent audio performance even better at some points from the Toshiba's commonly used in most Japanese amps BUT they DO fail if manage to come up at this age after all.
The type of failure is specific and your are not looking for a transistor that is shorted but a transistor that goes shorted or open Only if powered So this is not going to be easy to trace .
Fact 3
All Pioneer SA-9500II with no exceptions at this age will suffer from some contact or soldering issue ...so inspection for that is in order ( luckily this has not much to do with your problem ) this is a general service advice ( there is a remote possibility very rear in your case that you have soldering issues in the protection area )
Fact 4
All Pioneer SA-9500II with no exceptions at this age will suffer from some cleaning issue scratchy pots and switches also have nothing to do with the problem specified this is also a general service advice .
In reality
A) you need to trace if your problem lays on the amplifier that triggers the protection or the protection is at fault and auto triggers without amplifier problem .
B) To do that you need to observe offset before the relay ( before the protection ) at the time of the fault.
If offset remains low as checked before and in general anything less than 50mv but still protection is activated then the problem lays on the protection circuit .
C) if the offset is increased ( that can be any thing above 300mv (threshold point of protection ) up to full rail voltage when at fault , and protection is activated , measuring before the relay and before the protection Then the amp is at fault ....
Even more specifically:
---In case the protection is at fault suspects are in the specific order :
Q7, Q15, Q6 ,Q15,C13, C14, The protection circuit will also need a power supply to operate .You have a very detailed service manual observe and verify all voltage present according to the service manual if something is wrong there at the time of fault we will have to check the power supply that feeds the protection .
---In case the amplifier is at fault
The first thing you will have to look is the drivers of both amplifiers ...specific driver of NEC has a history of failure as described above.
---Finally this amplifier has separated power supply for the first stages of the amplifier From statistic point of view there have been reports for problems, there any loss of voltage there related to either soldering or capacitor issue will result activation of the protection ... ( area of Q8,9 )
The only possible way to trace a NEC transistor at fault IE during working and powered is a heat gun and a freeze spray ...If transistor in protection is at fault freezing it with a spray will momentary make it work and point you the problem Alike this can be done in the drivers and any other transistor that presents periodic failure ....Heat or cold will make it behave different and point you the problem ...A solution that works most of the times .
That's about it ...
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To save some time ..
Replacing a hand full of transistors to trace the problem is not an acceptable solution ( happened a million times before and user decided to replace anything to cure the problem ) this approach is a guarantee that this amplifier will never power up in the near feature .
Before you ask the answer is no MJE150xx drivers are not drop in replacements for the specific NEC drivers ...
devoted as a present to my good friend Depaj
Kindest regards
Sakis😀😀😀😀
Replacing a hand full of transistors to trace the problem is not an acceptable solution ( happened a million times before and user decided to replace anything to cure the problem ) this approach is a guarantee that this amplifier will never power up in the near feature .
Before you ask the answer is no MJE150xx drivers are not drop in replacements for the specific NEC drivers ...
devoted as a present to my good friend Depaj
Kindest regards
Sakis😀😀😀😀
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