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Need help fixing my Fender Mustang GT40 guitar amp

TiagoGuerra

New Member
Hi all!

First I would like to say that I really don't have great experience with electronics, apart from soldering some basic things, but I aprreciate any help you can give me!

I've been given a Fender Mustang GT40 guitar amp that has a problem. When I turn it on the LCD lights up but the Fender logo doesn't appear, and obviously it won't load the presets either, so I get no sound coming from the app. It appears to me that by some reason the operative system of the amp is not loading, and I've tried all the solutions I've come across the Internet of trying to turn on the amp while holding certain buttons to do firmware updates, or factory resets, or other things...

In some forums I noticed that other people had this problem too, but I couldn't find any solution anywhere. I've also tried to plug the amp to my PC via USB and do firmware updates, but when I turn the amp on I just hear the USB sound that you get when you connect something to the PC and nothing appears on the PC and nothing happens to the amp besides the LCD lightning up.

I've opened the amp but I don't see any broken solder joints or unplugged cables that could cause something like that.

Is there any way to unplug something on the amp that would cause a factory reset? I really need the amp to work since I don't have any other guitar amp at the moment.

Thanks for the help!
 
It sounds like either one of the power supply rails has failed, or some part of the main logic system has just died.

Can you post good clear and detailed photos of all the electronics & PCB, right from the power input to the display & USB connection etc?

It may be possible to recognise the power & voltage regulation parts, so you could do further tests.
 
Here are the pictures. I'm not seeing anything disconnected or burnt anywhere, so I really don't have a clue about what's causing the problem. Thanks for the help!
 

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Photo 8 shows a sub-board (with a black heatsink) in an edge connector. You could try removing the two screws that hold that PCB in & re-seat it in the connector by partly removing and refitting it a couple of times, then refit the screws? An open connector like that may be susceptible to tarnish over time.

Also, the board with the yellow transformer looks to have test points but the text is not very clear? More photos of that showing all the text could be useful.

It looks like the main control CPU is on the board that the display mounts to, below the display - the STM32F051C4U6

Photos of the back of that board may also be useful.
 
Thanks! I've tried to remove and refit the board but it didn't change anything. Here are the pictures of the back of that little board, the back of the one where the display is and the back of the display. And some pictures of the yellow transformer board
 

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The first step in troubleshooting electronic equipment is to verify that the power supplies are outputting their proper voltages and that these voltages remain stable throughout the range of current demands made by the circuitry that is powered. Do you have any service information that specifies what any and all power supplies in the unit should be outputting? Have you looked for forums that are specific to Fender amplifiers? There are many on the web. And best of luck.
 

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