Help Needed w/ Pioneer SX950

L

Lexx510

Member
Hi All,

I recently purchased a Pioneer SX950 for a $100. It's in fairly good condition. However, after playing for about an hour, I heard a minor hiss/pop and the sound went out. After some reading through these forums, I was able to narrow down my problem to the speaker protection relay. I noticed after powering on the unit, I don't hear the "click" of the protection relay. After cleaning the protection board with some Detoxit, the unit began to play again, but the sound went out again shortly after. Now, once again, the relay "click" does not engage after powering on the unit. Everything else lights ups and works.

My question is whether to replace the resistors and caps on the protection board or the speaker relay protector itself (the one that sits in the clear plastic case)?

Any help is greatly appreciated. Thank you!
 
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Lexx510 said:
Hi All,

I recently purchased a Pioneer SX950 for a $100. It's in fairly good condition. However, after playing for about an hour, I heard a minor hiss/pop and the sound went out. After some reading through these forums, I was able to narrow down my problem to the speaker protection relay. I noticed after powering on the unit, I don't hear the "click" of the protection relay. After cleaning the protection board with some Detoxit, the unit began to play again, but the sound went out again shortly after. Now, once again, the relay "click" does not engage after powering on the unit. Everything else lights ups and works.

My question is whether to replace the resistors and caps on the protection board or the speaker relay protector itself (the one that sits in the clear plastic case)?

Any help is greatly appreciated. Thank you!
Click to expand...
That's a steal, welcome to AK.
You need to rebuild the entire amp board and protection board at minimum. Based on your questions on what to replace, I would recommend hiring someone. Where are you located? An AK member may be able to help.
 
ivandezande said:
That's a steal, welcome to AK.
You need to rebuild the entire amp board and protection board at minimum. Based on your questions on what to replace, I would recommend hiring someone. Where are you located? An AK member may be able to help.
Click to expand...
Thank you for your response. I'm in Northern California in the Sacramento area.
 
Check the DC Balance and Idles on the amp boards.
Tell us what you recorded.
A DMM with a good set of micro grabber probes is needed. Never remove or place the probe clips on the amp board pins with the power on.
The procedure is in the service manual, found at HiFi Engine.
 
^^ What zeb said...^^

If that doesn't reveal something unusual, determine what is keeping it in protection (not allowing the relay to close).

The protection board (AWM-062) which ivandezande mentioned has various inputs to determine whether the relay is powered or not. Pins 5/6 and Pins 7/8 measure voltage at the emitters of the 8 output transistors for the L and R channels, respectively. Any consistent voltage present much over 500mV can prevent the relay from operating.
 
zebulon1 said:
Check the DC Balance and Idles on the amp boards.
Tell us what you recorded.
A DMM with a good set of micro grabber probes is needed. Never remove or place the probe clips on the amp board pins with the power on.
The procedure is in the service manual, found at HiFi Engine.
Click to expand...
Would you suggest testing in circuit (with the power off, of course)?
 
Watthour said:
^^ What zeb said...^^

If that doesn't reveal something unusual, determine what is keeping it in protection (not allowing the relay to close).

The protection board (AWM-062) which ivandezande mentioned has various inputs to determine whether the relay is powered or not. Pins 5/6 and Pins 7/8 measure voltage at the emitters of the 8 output transistors for the L and R channels, respectively. Any consistent voltage present much over 500mV can prevent the relay from operating.
Click to expand...
Okay, that will be my next step if something doesn't turn up on the protection board, thanks.
 
Don’t waste your time on the protection board. Get the amp settings first.
All it might need is an adjustment. Why make work if you don’t have to?
 
zebulon1 said:
Don’t waste your time on the protection board. Get the amp settings first.
All it might need is an adjustment. Why make work if you don’t have to?
Click to expand...
Good point. Now, I'm a rookie when it comes to all this, so please forgive all the questions. I only have a simple multimeter. How would I go about testing the amp settings? All the tutorials I've watched on YouTube have complex systems and they test while the unit is powered on. Thank you for all your help.
 
Amp setting tests are on page 38 of the Service Manual. It is a very good idea to get some mini-grabber clips to attach when making measurements and not connect and disconnect with the power on. If you short circuit the components in the process of moving clip leads with power on you can create a massive, expensive problem.
mini-grabber-hooks_.jpg
The measurements and settings described in the SM are done with power on.

And Welcome to AK!
 
merlynski said:
Amp setting tests are on page 38 of the Service Manual. It is a very good idea to get some mini-grabber clips to attach when making measurements and not connect and disconnect with the power on. If you short circuit the components in the process of moving clip leads with power on you can create a massive, expensive problem.
View attachment 1595089
The measurements and settings described in the SM are done with power on.

And Welcome to AK!
Click to expand...
Thank you for the welcome. I have been browsing these forums for a while just haven't posted. You are all so helpful.

I have a few questions before I attempt this procedure.

On the service manual instruction on pg. 38 it states:

2. Remove jumper plugs connecting Power In and Pre Out jacks.
3. COnnect 5.1 k-ohm resistor to Power In jacks.
4.Set power amplifier for no load."

I have never done this before and want to make sure I get it right before attempting. What do they mean by "remove jumper plugs?" Also, am I supposed to purchase an additional 5.1k-ohm resistor to connect to the Power In jack for this test? And how do I set the power amplifier for no load?

Thank you all.
 
Lexx510 said:
Thank you for the welcome. I have been browsing these forums for a while just haven't posted. You are all so helpful.

I have a few questions before I attempt this procedure.

On the service manual instruction on pg. 38 it states:

2. Remove jumper plugs connecting Power In and Pre Out jacks.
3. COnnect 5.1 k-ohm resistor to Power In jacks.
4.Set power amplifier for no load."

I have never done this before and want to make sure I get it right before attempting. What do they mean by "remove jumper plugs?" Also, am I supposed to purchase an additional 5.1k-ohm resistor to connect to the Power In jack for this test? And how do I set the power amplifier for no load?

Thank you all.
Click to expand...
Jumper plugs are silver colored short fat wires (they look like big staples) between Pre-out and Power-in jacks on the back. Remove means pull them out (power off, fingers usually work ok). Don't misplace them, no sound will come out if they are not plugged in.
You can just set the volume to minimum, center balance, input to Aux with no input, tone controls centered and/or defeated. You don't really need the 5.1kΩ resistors, they can be used if there is noise from the preamp causing a problem for the power amp during troubleshooting.
'No load' is no speakers or dummy loads connected.
Did you smell a peculiar odor or see smoke when the hiss-pop happened? That is the kind of noise a small capacitor makes when it fails. Consider removing the cover and looking for signs of trouble.
Do you have a Dim Bulb Tester? You will need one to safely test the amp so it does not go up in smoke, here is a link: https://audiokarma.org/forums/index...ial-please-feel-free-to-copy-and-post.875584/
Inexpensive and easy to build.
We are here to help!
 
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merlynski said:
Jumper plugs are silver colored short fat wires (they look like big staples) between Pre-out and Power-in jacks on the back. Remove means pull them out (power off, fingers usually work ok). Don't misplace them, no sound will come out if they are not plugged in.
You can just set the volume to minimum, center balance, input to Aux with no input, tone controls centered and/or defeated. You don't really need the 5.1kΩ resistors, they can be used if there is noise from the preamp causing a problem for the power amp during troubleshooting.
'No load' is no speakers or dummy loads connected.
Did you smell a peculiar odor or see smoke when the hiss-pop happened? That is the kind of noise a small capacitor makes when it fails. Consider removing the cover and looking for signs of trouble.
Do you have a Dim Bulb Tester? You will need one to safely test the amp so it does not go up in smoke, here is a link: https://audiokarma.org/forums/index...ial-please-feel-free-to-copy-and-post.875584/
Inexpensive and easy to build.
We are here to help!
Click to expand...


Okay, so I attempted the adjustment described in the manual. I turned VR3 and VR4 fully counter clockwise as directions state. I didn't have to adjust terminals 10 and 9 as they were already at 0V. Same for terminals 24 and 25. Terminals 12 and 13 were at around 5.26mv. Terminals 27 and 28 were at 0mv and adjusting didn't have an effect. I tried adjusting VR3 as stated in directions but it didn't seem to make a difference. Step 10 directs, "Allow to set warm up for 10 minutes then readjust." What exactly am I readjusting then? Below is a photo from testing terminals 12 and 13.
 

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Do you have a DBT? If that meter reading is really from pins 12 and 13 (bias measurement points) you have a serious problem that will get worse if not on a DBT. That indicates 5 amps of current flowing through the output transistors and resistors, or some other as yet unknown problem. Turn the power off until you have a DBT. Your meter appears to be on the 20 vdc scale, reading 5.17 volts.

Terminals 9 and 24 are ground (0vdc reference), and should have the black lead from the meter connected (clipped on) the for the appropriate measurements.
Terminal 10 is the output terminal for the left power amp, the red lead should be clipped on there and your meter should be on the DCV 2000m range. This range reads up to (actually just under) 2.000 volts (two volts). Very small voltages are often referred to as mV or millivolts. For instance 0.050 volts can also be referred to as 50 mV (50 millivolts). With the black lead on ground the readings may be positive or negative, the sign on the meter will tell you if it is negative. Sorry for over explaining if you already understood this.

EDIT: more info
 
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merlynski said:
Do you have a DBT? If that meter reading is really from pins 12 and 13 (bias measurement points) you have a serious problem that will get worse if not on a DBT. That indicates 5 amps of current flowing through the output transistors and resistors, or some other as yet unknown problem. Turn the power off until you have a DBT. Your meter appears to be on the 20 vdc scale, reading 5.17 volts.

Terminals 9 and 24 are ground (0vdc reference), and should have the black lead from the meter connected (clipped on) the for the appropriate measurements.
Terminal 10 is the output terminal for the left power amp, the red lead should be clipped on there and your meter should be on the DCV 2000m range. This range reads up to (actually just under) 2.000 volts (two volts). Very small voltages are often referred to as mV or millivolts. For instance 0.050 volts can also be referred to as 50 mV (50 millivolts). With the black lead on ground the readings may be positive or negative, the sign on the meter will tell you if it is negative. Sorry for over explaining if you already understood this.

EDIT: more info
Click to expand...

By DBT, I take it you mean Dim Bulb Tester? No, I do not have one and I'm not sure what to do with it if I get one. What do you mean by, "You have a serious problem that will get worse if not on a DBT?" I'm very new to all of this so pardon all the questions. Your help is much appreciated.

So what should be my next step? By the way, I should mention, throughout testing the protection relay did not click either.
 
Lexx510 said:
By DBT, I take it you mean Dim Bulb Tester? No, I do not have one and I'm not sure what to do with it if I get one. What do you mean by, "You have a serious problem that will get worse if not on a DBT?" I'm very new to all of this so pardon all the questions. Your help is much appreciated.

So what should be my next step? By the way, I should mention, throughout testing the protection relay did not click either.
Click to expand...

No problem with questions, please ask anything if you do not understand. Next step is build or buy a DBT. You can make a simple one with an old extension cord and a light bulb socket, or get as fancy as you want. The dim bulb tester is an incandescent light bulb (NOT CFL or LED) in series with the AC line input power to amp you are testing. It limits the power going into the amp so as to not damage things further. You plug the amp (or receiver) into the DBT. When the power switch on the receiver is turned on the light bulb will flash bright and then fade to dim on a 'good' unit. If there is a short or overload the bulb stays bright and you must turn off the power and trouble shoot with power off. Sometimes limited troubleshooting is done with the DBT connected, to verify some functions. Once the problems that cause the bulb to stay bright are fixed then you can go usually back to full power testing. I like to start with a 60 watt bulb, then increase to 100 or 120 watts when I have more confidence in what I am working on. The unit 'passes' the dim bulb test when the bulb goes dim.
The protection relay will not click until the failed power supplies, dc offset and any output overload are corrected. Sometimes there is a problem with the protection circuit, most times it is doing its job and protecting your speakers and amp. That can be determined during the process. On some units it will not click while on DBT, that is not necessarily a failure.
 
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merlynski said:
No problem with questions, please ask anything if you do not understand. Next step is build or buy a DBT. You can make a simple one with an old extension cord and a light bulb socket, or get as fancy as you want. The dim bulb tester is an incandescent light bulb (NOT CFL or LED) in series with the AC line input power to amp you are testing. It limits the power going into the amp so as to not damage things further. You plug the amp (or receiver) into the DBT. When the power switch on the receiver is turned on the light bulb will flash bright and then fade to dim on a 'good' unit. If there is a short or overload the bulb stays bright and you must turn off the power and trouble shoot with power off. Sometimes limited troubleshooting is done with the DBT connected, to verify some functions. Once the problems that cause the bulb to be bright are fixed then you can go usually back to full power testing. I like to start with a 60 watt bulb, then increase to 100 or 120 watts when I have more confidence in what I am working on. The unit 'passes' the dim bulb test when the bulb goes dim.
The protection relay will not click until the failed power supplies, dc offset and any output overload are corrected. Sometimes there is a problem with the protection circuit, most times it is doing its job and protecting your speakers and amp. That can be determined during the process. On some units it will not click while on DBT, that is not necessarily a failure.
Click to expand...
Ok, great. I will work on building a DBT and get back once I have one. Thanks!
 
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