Hi All,
Before I upgraded my Marantz PM7002 integrated amplifier, the left channel occasionally (sometimes every few minutes, but sometimes, every 10 min) will have some popping sound. It does not matter whether I put the amp in Class A mode or Class AB mode, the pop is still there. Sometimes the pop is a small one, but sometimes, it can really POP and make you jump, triggering the protection circuitry relay. I fear that it might damage my speakers. However, most of the time the POP is bearable. Do note even with no equipment (CD player etc) connected to the amplifier, it also pops, even when the volume is set to zero.
Hence, I thought it could be the caps at the power amp board. In fact, I upgraded both right and left channels caps to Nichichon MUSE caps, which immediately improved the sound stage. Other mods I did was to upgrade the OpAmps. The music coming out of this amplifier after modding is sounding very good except for the occasional popping sound from the left channel.
As the popping on the left channel is still there, this is what I did so far for troubleshooting to find the faulty component:-
1. I thought it could be the transistors. So I swap every transistor, one by one (while testing), between the Right and Left channels of the HDAM module and power amp stage. However, after swapping all transistors, the popping is still there.
2. I changed all the 1N4148 and Zener diodes to new ones. Every diode is changed to an exact replacement part. However, the POP is still there.
3. I've changed almost all the resistors at the power transistor stage to new ones, but the popping is still there.
4. I've tried knocking every component in the left channel, hoping to hear a popping sound when I knock on that component, it seems that the pop is not triggered by any components which are loose.
5. Remember the electrolytic capacitors have all been upgraded to Nichicon MUSE fine gold capacitors (both left and right channels).
However, after doing all the above, the left channel still occasional pops.
I'll try to upload the service manual for this amplifier here. But in the meantime, how would you troubleshoot such a problem? I am really out of ideas.
Is there any tool which I can debug this amplifier stage by stage in the power amp board to pinpoint the failing component. I suspect it could be a resistor... but which one?
Before I upgraded my Marantz PM7002 integrated amplifier, the left channel occasionally (sometimes every few minutes, but sometimes, every 10 min) will have some popping sound. It does not matter whether I put the amp in Class A mode or Class AB mode, the pop is still there. Sometimes the pop is a small one, but sometimes, it can really POP and make you jump, triggering the protection circuitry relay. I fear that it might damage my speakers. However, most of the time the POP is bearable. Do note even with no equipment (CD player etc) connected to the amplifier, it also pops, even when the volume is set to zero.
Hence, I thought it could be the caps at the power amp board. In fact, I upgraded both right and left channels caps to Nichichon MUSE caps, which immediately improved the sound stage. Other mods I did was to upgrade the OpAmps. The music coming out of this amplifier after modding is sounding very good except for the occasional popping sound from the left channel.
As the popping on the left channel is still there, this is what I did so far for troubleshooting to find the faulty component:-
1. I thought it could be the transistors. So I swap every transistor, one by one (while testing), between the Right and Left channels of the HDAM module and power amp stage. However, after swapping all transistors, the popping is still there.
2. I changed all the 1N4148 and Zener diodes to new ones. Every diode is changed to an exact replacement part. However, the POP is still there.
3. I've changed almost all the resistors at the power transistor stage to new ones, but the popping is still there.
4. I've tried knocking every component in the left channel, hoping to hear a popping sound when I knock on that component, it seems that the pop is not triggered by any components which are loose.
5. Remember the electrolytic capacitors have all been upgraded to Nichicon MUSE fine gold capacitors (both left and right channels).
However, after doing all the above, the left channel still occasional pops.
I'll try to upload the service manual for this amplifier here. But in the meantime, how would you troubleshoot such a problem? I am really out of ideas.
Is there any tool which I can debug this amplifier stage by stage in the power amp board to pinpoint the failing component. I suspect it could be a resistor... but which one?
I'm just going to jump in here (without seeing the circuit details) and say that this is typical of either a dry joint, typically on the driver transistors or VAS transistor (that's the one that feeds the drivers or, just as likely, an intermittent fault with one of those transistors. Unless the fault becomes permanent you will have a hard time diagnosing it. The clue to the transistor failure is observing the base/emitter voltage take a sudden increase over the nominal 0.65 or so present across the junction. The only practical way to be sure is simply to replace them. Check the soldering first though... and on any parts that run hot on that channel.
Here is the link to download the Service Manual for the Marantz PM7002 integrated amplifier.
PM7002 Service Manual
Proceed to page 15 and 16. This is the circuit diagram of the power amp section of the amplifier. You can clearly see the top left channel and the bottom right channel on these two pages.
Hence, how do I go troubleshoot the faulty component that is causing the popping sound.
PM7002 Service Manual
Proceed to page 15 and 16. This is the circuit diagram of the power amp section of the amplifier. You can clearly see the top left channel and the bottom right channel on these two pages.
Hence, how do I go troubleshoot the faulty component that is causing the popping sound.
Hi Mooly,
Is the driver transistor's clearly labelled
Left Channel (7281, 7285, 7279, 7283) ?
If yes I doubt it could be these transistors. So save cost and ensure it is the transistors, I did some swapping of these transistors with the ones from the right channel which are good and no popping sound.
This means I've exchanged all the Right hand transistors and installed on the Left Channel and vice versa.
(7281 <-> 7282, 7285 <-> 7286 , 7279 <-> 7280, 7283 <-> 7284) ?
However, the popping sound is still only coming out from the left channel intermittently. Right channel is clean and no popping sound.
Is the driver transistor's clearly labelled
Left Channel (7281, 7285, 7279, 7283) ?
If yes I doubt it could be these transistors. So save cost and ensure it is the transistors, I did some swapping of these transistors with the ones from the right channel which are good and no popping sound.
This means I've exchanged all the Right hand transistors and installed on the Left Channel and vice versa.
(7281 <-> 7282, 7285 <-> 7286 , 7279 <-> 7280, 7283 <-> 7284) ?
However, the popping sound is still only coming out from the left channel intermittently. Right channel is clean and no popping sound.
7279, 7281, 7283 and 7285 are the output transistors. Those are the ones that almost certainly are OK 🙂 Its the small ones that fail... and the failure mechanism is strange but one I have encountered many many times as a service tech.
So the drivers are the ones in front, 7277 and 7275. There are also pre drivers on this one which are 7271 and 7273. Those could also be worth looking at. You might find that swapping them 'fixes' the issue as heat from the iron can affect the junction within the device. BF422/423 were a once common part used in TV's.
Beyond those and its still favourite to be a faulty transistor (or dry) but finding by measurement is difficult unless the problem is regularly occuring. Typically an oscilloscope with isolated probes would monitor the base/emitter junction and you would look for spikes that exceed the 0.7 volt or so maximum that can occur across a silicon forward biased junction. If the fault was permanent then a meter would show the raised voltage over the junction.
So the drivers are the ones in front, 7277 and 7275. There are also pre drivers on this one which are 7271 and 7273. Those could also be worth looking at. You might find that swapping them 'fixes' the issue as heat from the iron can affect the junction within the device. BF422/423 were a once common part used in TV's.
Beyond those and its still favourite to be a faulty transistor (or dry) but finding by measurement is difficult unless the problem is regularly occuring. Typically an oscilloscope with isolated probes would monitor the base/emitter junction and you would look for spikes that exceed the 0.7 volt or so maximum that can occur across a silicon forward biased junction. If the fault was permanent then a meter would show the raised voltage over the junction.
Hi Mooly,
Problem is I don't have a scope, just a trusty digital multimeter. I was actually thinking of breaking down the left channel in order to determine which part of the main power board the problem is coming from.
I've thinking of dividing the left channel into 2 parts, separated by the pair of resistors 3315 and 3313. Hence before the signal reaches these resistors, I would call this section the Input stage. After these resistors, I will call it Output stage.
Now, since the right channel was functioning properly, I was thinking of crossing the Input stage and Output stages between the left and right channel.
For example:
Left Channel: Input Stage ----> Right Channel: Output Stage
Right Channel:Input Stage ----> Left Channel: Output Stage
Since both left and right channels are exactly the same and is derived from a single power source.
I tried by wiring the above schematic, but somehow, the amplifier went into a hang mode and humming sound coming out from both channels. I fixed it back to original state and thank God, the amp was still ok. I might sound crazy, but I'm running out of ideas and getting desperate to pin point the problem.
I don't want to simply go replace all transistors as they are quite costly. Hence I want to find out the faulty component.
I also noticed that the popping sounds comes after the amplifier has warmed up by supplying music to it for around 5 min, it will start popping on the left channel.
Problem is I don't have a scope, just a trusty digital multimeter. I was actually thinking of breaking down the left channel in order to determine which part of the main power board the problem is coming from.
I've thinking of dividing the left channel into 2 parts, separated by the pair of resistors 3315 and 3313. Hence before the signal reaches these resistors, I would call this section the Input stage. After these resistors, I will call it Output stage.
Now, since the right channel was functioning properly, I was thinking of crossing the Input stage and Output stages between the left and right channel.
For example:
Left Channel: Input Stage ----> Right Channel: Output Stage
Right Channel:Input Stage ----> Left Channel: Output Stage
Since both left and right channels are exactly the same and is derived from a single power source.
I tried by wiring the above schematic, but somehow, the amplifier went into a hang mode and humming sound coming out from both channels. I fixed it back to original state and thank God, the amp was still ok. I might sound crazy, but I'm running out of ideas and getting desperate to pin point the problem.
I don't want to simply go replace all transistors as they are quite costly. Hence I want to find out the faulty component.
I also noticed that the popping sounds comes after the amplifier has warmed up by supplying music to it for around 5 min, it will start popping on the left channel.
Get a fan to blow at it then. Confirm the case first. Then get a smaller fan and make funnels / air guides out of paper to blow less things at once.
Also this may sound stupid, but have you checked the relays? (Including the circuit powering/controlling it)
Hook-type probes to connect specific points in the circuit to a sound card comes in really handy in times like this.
So far, you've been looking at the output stage. The tone/balance board is between the volume control and power amps and lots more opportunities for problems there too. You tried swapping power amplifier input leads, but have you operated it simply disconnected? According to the schematic, connector 1251 is mirror imaged for L/R channels and only carries signal + ground for both power amps. I don't see how swapping that around could have upset the amplifiers other than by it's ground connections - that's probably where there was a problem with the protection sense circuits.
In any case, if that problem returns when you pull the plug, you could just as easily ground the signal+ at the plug, where the signal inputs are DC isolated by caps.
In any case, if that problem returns when you pull the plug, you could just as easily ground the signal+ at the plug, where the signal inputs are DC isolated by caps.
A ex boss of mine used to swear by freezer spray.
You spray it on one component at a time and see if the popping gets better or worse.
You spray it on one component at a time and see if the popping gets better or worse.
^ Another vote for freezer spray. Don't blast the parts as that cools everything nearby, just drip (takes practice with the nozzle) a drop at a time onto the transistor.
Replacing or swapping any transistors around the output stage will cause the bias current to alter... and so it needs resetting as per the manual.
Replacing or swapping any transistors around the output stage will cause the bias current to alter... and so it needs resetting as per the manual.
- Status
- Not open for further replies.