Mustang GT/GTX - Random Audio Dropout fix

Started by admin, May 15, 2020, 01:47:37 PM

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admin

If you have Bluetooth and Wi-Fi disabled, and Amp continues to have audio dropouts. Do these tests :

#1-Test Headphone Output, connect Headphones (Headphone Output jack is a switching type which mutes the speaker)-try playing for an hour on headphones only -if Amp works, problem might have been a oxidized contact on Headphone output jack.
But if Amp still cuts out after 10 minutes, on Headphones only,  then proceed to step #2

#2 disassemble Amp to access the internal PC Boards, (take several pics with smartphone)  inspect the ribbon cables (they are often glued to the PC Board -the IDC header ribbon cable connectors may have become oxidized and resetting the ribbon cable may restore electrical connections.

#3 DSP Board connection-there is a small DSP board which employs a PCB plated finger edge connector ( like a DIMM Memory inside a PC) -these connections may have become oxidized, use an anti static wrist ground strap (to minimize ESD static discharge damage)  gently remove DSP board, and reseat in its PCB to PCB connection.

https://www.vguitarforums.com/smf/index.php?topic=28568.0


I do agree Fender needs to do a failure analysis on the faulty units that exhibit random Audio Drop outs, and perhaps implement an ECO(Engineering change order) to use a higher specification Ribbon cable and Male header

Or test for faulty flux removal of the SWITCHING HEADPHONE JACK.



If the Headphone Jack is occupied, or if there are broken solder joints on the headphone jack, no sound emerges from the internal 12" Speaker
An unoccupied Headphone Jack with WORKING CONTACTS is essential for the Mustang amp's Speaker  to continue working and not cut out


The Headphone Jack is unsecured low cost vertical PCB Mounted 3.5mm TRS Switching jack, and any side to side tugging on the headphone jack cable WILL compromise the internal PCB solder connections on the switching contacts, and create random Audio drop outs.

   

Above right (Blue Circle)  Inspect the Headphone Jack PCB Mounting pads for any breaks, cold solder joints, etc  - these solder pads can easily weaken if a headphone cable plug was tugged too hard.

If your Headphone Jack is broken - here is a replacement

Fender Part Number:   008-2046-000

https://www.amplifiedparts.com/products/35mm-jack-fender-stereo-phone-mustang

(Same Jack above can also be used to replace a broken Aux input jack



The Headphone Jack analog circuitry is among an array of signals for sensing the front panel controls on the common Front Panel Ribbon Cable (Blue Circle above) connected to the CODEC Board

Its a 16 pin (0.100") IDC Ribbon cable


I observed the production line applies a small dab of clear RTV glue on this 16 pin IDC plug to keep it connected to the 2x8 (.100") PCB Male Header on the CODEC board , but often this plug along with the contact former dielectric base on the Male Header can still vibrate free


DSP Board is in the Blue Circle above -   
-The DSP board which employs a PCB plated finger edge connector ( like a DIMM Memory inside a PC) see the edge connector on the far left.
Some report gently removing the DSP board two screws, and re-installing the DSP board in the edge connector fixed their random audio dropouts     

If ANY electrical contact in any of the Blue circles above are weak or compromised  - this results in random  audio drop outs

Luckily None of my Mustang GT / GTX amps have exhibited this random Audio drop out problem, but Ive posted the likely areas where to look in the circuitry to implement corrective action.

ccoolavie

Hello,
I have to thank you for your post.
I will get a look after my own investigation.

I owned the mustang GT40 and I have this weird volume drop issue.
Sometimes, I can play tens of minutes and sometimes it happens after a few seconds.
I am wondering if it is not more related to software or internal processing going wrong.
I have told that it can be due to noise reduction, so I am curreltly trying different "eq & amp settings"

Let's get in touch.

ccoolavie

Sharing an audio sample of the volume drop issue

admin

#3

DSP Board is in the Blue Circle above -   
-The DSP board which employs a PCB plated finger edge connector ( like a DIMM Memory inside a PC) see the edge connector on the far left.
Some report gently removing the DSP board two screws, and re-installing the DSP board in the edge connector fixed their random audio dropouts     



tp4surf

     I purchased a used GT40 from a private party about 6 months ago. I carelessly didn't research "GT40 problems and issues", and to be honest, it was at least a month of frequent use before the notorious "volume drop" issue appeared. Since then, I have researched and applied all of the documented "fixes" I could find, including disable WiFi/BT, clean/reset ribbon cables and other cables, reset DSP CB, firmware upgrade, forced reset, etc. None of these fixes worked for longer than a week or so. I contacted Fender who said the only fixes were the "WiFi disable" and/or the "ribbon reset", but since I had already done these, and the GT40 was "discontinued" no other fix was available from Fender.
   
     Has anyone discovered a permanent fix for this issue, other than a electronics recycling site? Or, even a creative re-purposing?


philjynx

Quote from: admin on May 24, 2021, 04:38:11 PM
....
-The DSP board which employs a PCB plated finger edge connector ( like a DIMM Memory inside a PC) see the edge connector on the far left.
Some report gently removing the DSP board two screws, and re-installing the DSP board in the edge connector fixed their random audio dropouts     
....
Could this be a candidate for removal of the DSP board and cleaning both the edge of the board and the PCB socket with switch cleaner?

That's what I would do.

tp4surf

Did that...twice.  Did the same with every other cable I could get to. Asked Fender where the ribbon cable terminated and how to get to it so that I could reset that end. Fender not willing to advise due to "liability and legal concerns". BTW, amp was on all day yesterday and turned it on this morning around 7a, practiced for a couple of hours, left it on, and no vol issues...yet.

tp4surf

So, audio-drop re-occurred, and this time I cleaned all the connections I could get to with a pencil erasure followed by a good dose of Deoxit. Lasted several weeks, and I thought I had it fixed. But, of course not...failed again a couple of weeks ago, Re-read the bit above about the 3.5mm audio jack on the recommendation of someone from the Mustang FB Group. Wiggling the headphone jack seemed to produce the audio drop, so I ordered a replacement.  Pinned-out the new jack before installing it, checking continuity with and without a dummy male jack. Removed the old jack and re-soldered the new jack. Checked the continuity of pins from the soldered side of the PCB, and no issues. Put everything back together, powered-up and no audio! Everything else works fine, but no audio without headphones, no audio with headphones, no audio through Aux jack in and no audio when paired to BT. The "make/break" circuit not working, maybe a pin pad was damaged or lost? Was there something I else that may have caused the failure? Searched, but unable to find a replacement daughter-board, Someone posted that they a manufactured by Golden Bow in China, and not available through retail channels. Probably not worth the effort. Maybe cannibalize a "retired" GT40? Convert to speaker Cab? Open to suggestions...

admin

Quote from: tp4surf on July 25, 2022, 11:44:45 AMSo, audio-drop re-occurred, and this time I cleaned all the connections I could get to with a pencil erasure followed by a good dose of Deoxit. Lasted several weeks, and I thought I had it fixed. But, of course not...failed again a couple of weeks ago, Re-read the bit above about the 3.5mm audio jack on the recommendation of someone from the Mustang FB Group. Wiggling the headphone jack seemed to produce the audio drop, so I ordered a replacement.  Pinned-out the new jack before installing it, checking continuity with and without a dummy male jack. Removed the old jack and re-soldered the new jack. Checked the continuity of pins from the soldered side of the PCB, and no issues. Put everything back together, powered-up and no audio! Everything else works fine, but no audio without headphones, no audio with headphones, no audio through Aux jack in and no audio when paired to BT. The "make/break" circuit not working, maybe a pin pad was damaged or lost? Was there something I else that may have caused the failure? Searched, but unable to find a replacement daughter-board, Someone posted that they a manufactured by Golden Bow in China, and not available through retail channels. Probably not worth the effort. Maybe cannibalize a "retired" GT40? Convert to speaker Cab? Open to suggestions...

Sad story

These amps are fragile

Used GT40 pop up on Craigslist cheap , most Fender service centers refuse to work on these amps, because they often fail within the 30 day repair warranty period

gogogoch

My GT40 has just recently started some weirdness, and I'm not sure if it's the same "audio dropout" problem that this thread refers to.  It seems to kick in at some random interval after I've been playing for a bit, and sometimes resolves itself after I change presets a few times, but often it persists until I turn the amp off for a little while.

The output level drops, but not completely "out", and the sound changes a lot. Short, sharp sounds are accentuated (for example, the percussive sound of the pick hitting a string will still sound clear), while the rest of the sound is muffled.  If I let the strings ring, after several seconds the volume will suddenly jump up, for the rest of the sustained note. It sounds like a compression effect (that's set really badly) -- but it happens even on presets that don't have a compressor in the chain.

Is this the infamous audio dropout that might be fixed by the steps recommended above? Or is this something else? Any suggestions about how to fix?

Many thanks.

BedroomPlayer74

Thanks for sharing!

I'm sure this would've been mentioned if true but I must ask - is there any risk of shock if I'm poking a screwdriver around the innards of this amplifier ?  (Yes, I have disconnected the power cable  ;)

admin

#11
There are dangerous high voltages present- use a wooden chop stick to wiggle internal  wires /ribbon cables to determine source of audio drop outs while powered on.

Old rule when working on amps -  keep your left hand in your pocket to avoid high current passing through your heart


And remember this whole thread, and Fenders abysmal support on DSP products  before considering buying that new $1500 Fender Tonemaster Pro

Elantric

Fender's policy in January  2024 is to officially provide Service Repair for any Mustang GTX owner experiencing Audio drop outs - contact Fender Customer Service if you have any problems with your Mustang GTX and obtain service