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Post subject: I don't get any sound
Posted: Sun Feb 10, 2013 2:57 pm
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Hi. I dont' get any sound from my Mustang I. I checked all the flat cables connectivity between PCB's everything is ok. All connectivity to the speaker, everything is ok. But I have no sound at all.

If I use the "phones" option I can hear everything. Anyone had the same problem? What should I check...resistors, condensators etc etc? Any in particular?

Thanks for any possible help.


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Post subject: Re: I don't get any sound
Posted: Sun Feb 10, 2013 3:46 pm
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SKcoppertele wrote:
well I would say that you can return it and get a new one.... but by opening it you voided the warranty...


what warranty. It's gone long ago.


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Post subject: Re: I don't get any sound
Posted: Sun Feb 10, 2013 5:34 pm
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the speaker must be broken.


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 1:28 am
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pet415 wrote:
the speaker must be broken.


I will hook it with another amp to see.


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 2:15 am
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Quote:
the speaker must be broken

Not necessarily. It could be the power amp, the connectivity* between the pre-amp/DSP and the power-amp input, the connectivity from the power amp output to the speaker, the power supply to the power amp, ...

A simple test would be to connect a voltmeter on its "AC volts" setting, across the speaker terminals (with the speaker still connected to the amp) and play the guitar (obviously make sure the volume is turned up, etc). If a voltage registers, then you know the electricity is getting as far as the speaker - in which case yes it could be the speaker at fault. If there's no voltage here, then the problem is earlier. Repeating the test at other points in the signal chain will help narrow down exactly where (as you already talk about testing individual resistors, capacitors, etc, I assume you have the equipment and will know how to do this).

Another possibility, as you mention having used headphones: as you know, plugging in headphones mutes the speaker. When you unplug the headphones, it's possible the little switch in the headphones socket that controls the speaker muting is stuck. Try inserting and removing the headphones jack a few times, maybe squirt a little contact cleaner into the socket - that could free-up the switch. Always worth trying the simple things before attacking the innards of the amp!

*I note you say the connectivity's ok - you don't say whether that's based on a visual inspection or electrical test. If visual, then I'd suggest doing the electrical test; connectors can look fully in-place but not be making an electrical connection.


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 2:25 am
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scott-uk wrote:
Quote:
the speaker must be broken

Not necessarily. It could be the power amp, the connectivity* between the pre-amp/DSP and the power-amp input, the connectivity from the power amp output to the speaker, the power supply to the power amp, ...

A simple test would be to connect a voltmeter on its "AC volts" setting, across the speaker terminals (with the speaker still connected to the amp) and play the guitar (obviously make sure the volume is turned up, etc). If a voltage registers, then you know the electricity is getting as far as the speaker - in which case yes it could be the speaker at fault. If there's no voltage here, then the problem is earlier. Repeating the test at other points in the signal chain will help narrow down exactly where (as you already talk about testing individual resistors, capacitors, etc, I assume you have the equipment and will know how to do this).

Another possibility, as you mention having used headphones: as you know, plugging in headphones mutes the speaker. When you unplug the headphones, it's possible the little switch in the headphones socket that controls the speaker muting is stuck. Try inserting and removing the headphones jack a few times, maybe squirt a little contact cleaner into the socket - that could free-up the switch. Always worth trying the simple things before attacking the innards of the amp!

*I note you say the connectivity's ok - you don't say whether that's based on a visual inspection or electrical test. If visual, then I'd suggest doing the electrical test; connectors can look fully in-place but not be making an electrical connection.


The connectivity checking was electrical. But without a schematic of the amp it will take longer. Actually I thought about the headphone jack problem. No worries on verifying the things, I made my own tube amp ;)


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 8:14 am
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If you got his far I would recommend disconnecting the speaker and replace by any other 8ohm (at least) speaker you might have around. Make sure you don't short the two power amp outputs or you may blow it for good (if it has no short protection)

If you don't have any speakers, but you have a 3.5mm headphones female socket, you can try it with your headphones.

You may also check for continuity on the speaker coil, you should have a resitance of 1-3 ohms maybe.

Make sure of taking a detailed picture of the power amp section of the board, maybe if the power amp IC died it can be replaced for a couple dollars, but you need to identify it first. If you post the picture we can give a hand


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 3:03 pm
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jedi2b wrote:
If you got his far I would recommend disconnecting the speaker and replace by any other 8ohm (at least) speaker you might have around. Make sure you don't short the two power amp outputs or you may blow it for good (if it has no short protection)

If you don't have any speakers, but you have a 3.5mm headphones female socket, you can try it with your headphones.

You may also check for continuity on the speaker coil, you should have a resitance of 1-3 ohms maybe.

Make sure of taking a detailed picture of the power amp section of the board, maybe if the power amp IC died it can be replaced for a couple dollars, but you need to identify it first. If you post the picture we can give a hand


Well I did the other way around. I connected the fender mustang speaker to my tube amp and it worked fine.
Is there any schematic available to check easier where the power amp is etc etc? I hope I have some time this weekend to do it.


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 3:40 pm
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nope, there are no schematics and Fender told me that they are not going to make them public either, so your best option would be to try to determine if it is the power amp section that is in trouble, most probably and IC audio amplifier.

Really worst case, you can build your own 20 or 40 watts solid state power amp for 10 bucks and take the signal from the master volume knob. take a look for example to the lm3886 typical application circuit. 38 watts over 8ohms and it would even work with the mute switch on your phones connector. the whole PCB could not be greater than 10x10 cm so you can even fit it into any available space inside the amp.
http://www.ti.com/product/lm3886


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 4:34 pm
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jedi2b wrote:
nope, there are no schematics and Fender told me that they are not going to make them public either, so your best option would be to try to determine if it is the power amp section that is in trouble, most probably and IC audio amplifier.

Really worst case, you can build your own 20 or 40 watts solid state power amp for 10 bucks and take the signal from the master volume knob. take a look for example to the lm3886 typical application circuit. 38 watts over 8ohms and it would even work with the mute switch on your phones connector. the whole PCB could not be greater than 10x10 cm so you can even fit it into any available space inside the amp.
http://www.ti.com/product/lm3886


Hmmm..actually I will follow the patch from the master volume knob I guess... Ok so other detail. My usb connector deconnected (well I sat on it when pluged and the connector got loose). So I soldered it back in..and having into account that it is so close to the headphones socket..something might have happened..I will check the headphone connector exhaustivelly. Actually I only use the Mustang for headphones training...for the bang I use my own made tube amp or my big commercial one ;).

But the lm3886 is really a nice option tnx.


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Post subject: Re: I don't get any sound
Posted: Mon Feb 11, 2013 9:03 pm
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If the only thing you broke siting on it is the USB port you are either very lucky or very skinny.

Anyway, with this multilayer circuit boards, there's always the risk that excerting a lot of pressure maybe the board is broken somewhere even if you don't see it, or a connection got desoldered and broken loose.


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Post subject: Re: I don't get any sound
Posted: Tue Feb 12, 2013 12:33 am
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When you say "The connectivity checking was electrical" - do you mean you've just put an ohm-meter across the connectors at various points? Or have you done the audio tests I suggested earlier? I really think the latter would be a useful next diagnostic step.


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Post subject: Re: I don't get any sound
Posted: Tue Feb 12, 2013 2:56 am
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jedi2b wrote:
If the only thing you broke siting on it is the USB port you are either very lucky or very skinny.

Anyway, with this multilayer circuit boards, there's always the risk that excerting a lot of pressure maybe the board is broken somewhere even if you don't see it, or a connection got desoldered and broken loose.


The usb connector is in another small pcb platform that is connected to the main PCB, so the metal part just twisted a little bit. the tiny "buffer" pcb was ok.
The speaker was working when I broke it. I was really busy at the time and 2 months later I had no sound.


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Post subject: Re: I don't get any sound
Posted: Wed Feb 13, 2013 10:07 pm
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Well, the fact that you know that you broke the USB connector & then the speaker didn't work should give you a good idea where to start looking. I hope it's not a component level problem, 'cause you will have trouble finding any "condensators" to check. Being as it is an American designed amp, it uses capacitors ;)
Good luck, & it's probably something simple, usually is.

Cheers,
kev


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Post subject: Re: I don't get any sound
Posted: Mon Jun 03, 2013 8:57 am
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Hi. So Finally after months I had time to fix my mustang.
I checked the connectors and the audio plug that goes the headphones is working fine.

However I could have a little help on knowing which paths to check with audio flowing through. Or is there an easy way to check the poweramp directly?


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