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Input Output volume drop Problems SOLVED !

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The pins of the connection from input output board (1 to 6) to the A/D Board are shorten to the back casing.

Isolating the caseing in this area whith tape solved the problem.


nice mixing everyone

M20D Rocks


(pictures come later)


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Finding  the key problem of volume drop issue. (the story)


I've done an deeper research in my m20d to find were te problem comes from.

During the process i recunstruckt the input circut, simulated it, mesured all voltages and added components.


First the known results what could happen.:

On mine it effects channel 1 to 2 , 3 phantom power on. Mostly after a time of low signal input the signal droped.

Then when you touch the Mic or make an loud signal to the Mic the Mic volume comes up again.

On my rode M2 first the signal distorted then it plops and all is normal again.

On an recoded error i saw that the signal was cutted in the upper wave.

Push an pull will result in signal drop. Strange that push an pull forward and backwards off every channel will result in an volume drop on channel 2 or 3.

an short clip:



touch the Mic

loud input signal to the Mic

chance preamp volume

grounding the mixer internally (helped but not fully maybe the open and close process, and reconnecting the ribbon cabels brings lost connections back, so problem is gone)


what it is not:

the Mic's

the Mic cables

the input jack's

the a/d chips

an DC offset


what it could be:

the gain setting in the mic preamp dropped to 0 db (pga2505)

anything in the input from the Mic to the a/d chip

an DC offset

an short from in output board to the case (that is it!)

bad connections in the ribbon cables (in my case)


thoughts about the key problem:

if it's an gain Drop to 0db in the mic Preamp (pga2505) there must be an fail in the serial communication to the chip.

That could happen if enable pin (cs) gets ground signal, an the clock(sclk) signal is present.  The sdi pin is ground an so it sets all bits to 0 what means gain 0db. On display the gain setting is ok but the preamp has the wrong value. To get the right value you can bring the input signal up so the trim tracking option will reduce the singal by 3db witch sets the preamp value new. Or you set the gain setting by hand. Somtimes you must gain up 3db to bring the gain up again. That's because the pga2505 has only 3db gain steps.  

if it's an DC offset :

maybe an DC offset before the preamp because there are no DC symmetry resistors

maybe the offset is produced by the 48v phantom in combination with the open coil and capacitor in the line in section of the Mic input.

The offset could be in the input circuit of the a/d chip (but i think there is symmetry grounding)

If'e put an symmetry grounding in the input before the preamp(pga2505)but it not solve the problem.

My wife had the idea of could be an short to the case. And it was.

Finally what solve the Problem:

Three layers tape to isolate the case in the right place. And an row hot glue to make more space to the case.


First all was good but three weeks later the problems came back. Channel 2,3,4 began to drop signal. 

So i checked the internal ribbon cabels, an found bad IDC connections on both end's .

I repressed all IDC's and used contact spray on the socket strips. For now that solved the problem.









hot glue , ribbon cables whith IDC socket strips


for the freak's:

input preamp texas instruments PGA 2505I

a/d chip circus logic cs5364-cqz



nice mixing everyone

M20D Rocks

Edited by wersonnst
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OK so let me see if I am understanding this, I think that I may have been experiencing this.  I've tried changing mics, cables.. and it only happens occasionally. 


Sometimes when I step up to the mic to sing after I've maybe stepped back off the mic for short period of time, the level is really low but singing into it kind of "wakes it up" and then the volume stays up for the remainder of the passage.


I thought it might have been some kind of gating issue in my voice live 3 but it kind of sounds like what you are describing here.  I believe I have managed to turn all the gates off in the voice live 3 at least all that I can find.


Does this sound like what you are talking about? 

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: litesnsirens

That's exactly what happend's.

For me i figured out the problem is after the mic preamp and before the A/D converter. And there are the cable connections.

I use my M20d every week so if there were new or other problems I will report. The last weeks there where no problems.  :)


nice mixing everyone

M20D Rocks

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  • 4 weeks later...


It could be the same Problem.


Until there is warranty  please contact Line 6  and open an service ticked. They will help you.


If you are familiar with working on elektronics. And on your own risc.

You can open it and check:

For bad connections in the  ribbon cables  and IDC's.

Bad soldering.

Oxided connectors.

Broken Jacks.

The circutboards.

Connections to the case.

Everything else.

If possible and nessesary, messure Connections and Voltages.



So Problems on mine M20D are Back. First Chanel 2 than an week later chanel 2 ,3 ,4 .

I opend it an checked my isolation to the case , witch was ok. So I messured the ribbon cables and found bad connections in the IDC's on both end's. Repressing the idc's and contact spray on the socked strips solved the problem.

Now it's fine again , hope it will be for more than a few weeks.


nice mixing everyone

M20D Rocks

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Hi wersonnst,


the 'VolumeDropFeature' nearly killed my 250pax gig on Saturday evening this weekend.

During perfomance the acoustic guitar on input 1 and the female lead singer on input 4 'disappeared'.


At the sound check i already noticed the 'VolumeDropFeature' on the digeridoo, but i just exchanged the mic SM57

because i thought the SM57 was broken.


I searched this forum and now i believe that the root cause is the lousy hardware design and failing quality control of the M20d.


Circuit boards scratching at the metal casing?

Internal cable connectors loosing contact?

Grounding lost causing trouble?


I really like the M20d, but those hardware design flaws drive me crazy...

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Mine is on it's way back from Line6 where it was worked on for the same issue.  The notes on the help ticket say that the grounding clips on the I/O board were cleaned and then tested to spec.  Should be back in a couple days and I'll let you know how it works.


Anyone know a good method for testing this out?  I'd really like to give her a shake down cruise when it gets back.

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I read on the Line 6 forum an old post regarding channel volume drop. I have recently been experiencing the same problem. I couldn’t find any solution so wondered if you can help.



My set up:



Line 6 L3t x2 (connected via L6 link)




Line 6 HD Pro

Acoustic guitar direct

Bass guitar direct

Keyboards (Stereo)

Backing vocals (Shure sm 57 with mic lead)

Backing vocals (mic headset)

Lead vocals (Line 6 wireless modelling mic)


The channels that have caused problems are the lead vocals & Bass guitar. The bass guitar at the weekend disappeared after our 1st song at a gig with no volume, this was rectified once I switched off the M20d and back on again, this has happened a couple of times. We also have repeated problems with the volume dropping on the main lead vocals.



We are a busy gigging band in the UK so need a reliable setup. We also use the iPad connection through an Apple device. I hope this info is useful and any help would be much appreciated.


Any help would be much appreciated.

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Wow this thread and some others I have read seem to point a very common type of issue.   It would appear to me that some type of change has taken place over older versus newer M20d or just plain build quality.


I "had" a M20d, still have one if I'm fair but have not seen it very quiet some time!  It started exhibiting all the common modes of failure, channel level drops, left main out output fading then recovering, working fine for 3/4 of a gig then fading for a while etc etc.  You can put this down to some or all of the issues that have been highlighted in previous posts.  My view it's a common  hardware fault so updates, patches and all the iApps! in the World won't fix it.   If you have this issue and it's within warranty then send it back to be resolved, pain in the arse but it's the only way. 


So FYI, for those of you out there and it's not a great story so far.  Dropped off the unit April 10th 2015 at Guitar Guitar Glasgow, they did point out at the time that they were experiencing a few issues with turnarounds citing the Yamaha>Line6 take over.  Didn't think much of it until I phoned for an update May 10th and May 29th both times the key component (circuit board) assume this is the input board as looking at the picture(s) doesn't look like there are many others had an Estimated date 15th August 2015.   Potentially five and a bit months down time in the first year!!! if this is indicative of all the other things reported around the M20d, the Line 6 MTTR and MTBF must look shocking. 


Shout out to the guys at Guitar Guitar, they have been great :D but they really can't do anything with regard to internal parts delivery


Anyone from Line6 listening?



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Heavy speculation on my part to follow, take with a grain of salt:


I think L6 recognized a problem.  There was a break in production for unknown reasons but I'm GUESSING it was to fix said problem.  They've been very generous about taking these back to the shop for warranty work.  They've said that production is back on and the backlog of orders is filling.  Just my guess that grounding is the issue.


They took mine back with almost no questions asked and it was even a couple months past warranty.  The turnaround for mine in the US was very quick.  I should get it back today and that was barely a week.


If you're having this problem, my recommendation is call Line 6.  Unless you're super tech savvy there's not much you can do on your own.


Maybe one of you super tech smart dudes could do a youtube on how to fix the grounding issues for out of warranty M20D's?  Maybe even Line6 could do it?  That might take some of the heat.


I've used Line6 products for a long time and as a company they are notoriously close lipped on design bugs.  However, I've always found their service center to be really good.  When you consider that they're ALWAYS making products on the cutting edge of technology, I can expect some bugs.  Knock wood, I've been pretty lucky so far.


FWIW my backup mixer has a bad channel and the Allan and Heath mixer that I replaced with the M20D had some issues.  Maybe it's just part of the territory?

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OK ... I have another question on this issue, as I have had other issues.  Thinking about it now I think they may be related.  So first, inputs 13/14 at first one channel would drop out randomly, took it in to Long and McQuade here in Canada for repair, now it just makes a lot of noise but I guess I should be happy that I have both channels.  In reality I can't use those channels.  Long and McQuade are authorized to do repairs on the Line 6 gear and I typically trust them but I think they may not have been aware of this problem at the time I took the unit in for repair. 


The second issue is with the headphone jack, on a fairly regular basis if I monitor through the headphone output one side would drop out.


Aside from the issue of my vocal mic dropping out (inputs 1 & 2) all these inputs/outputs seem to be on that front row, 13/14 and the stereo headphone out.  These all seem like they could be grounding issues.  It's starting to make sense to me now... there are just too many issues going on in that front row or input/outputs to be coincidental.  Hopefully if there is a fix available that is understood, I can get it done and have a mixer that I can use all channels on the board.  With any luck since my board is no longer under warranty, I can get a support ticket underway and get this repair done for no charge. 

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As a general rule, I don't trust authorized Line6 service centers unless it's something pretty vanilla.


For example, I had a Vx 700 that started acting up.  WELL beyond warranty and gigged with extensively, even went to Iraq with me. Anyway, the Phoenix Line6 authorized store could not fix it after 2 trips I decided just to wait for the JTV to come out.


I had a POD footswitch go bad and there's youtube's on how to fix that yourself, so I figured they could handle that and they did a good job.


When I called Line6 about my M20D problems, they didn't even recommend the local repair, they immediately issued an RMA and I send it to the mother ship.


My advice, skip the retailer or local tech.  Go right to the big brains at Line6 and see if they'll take it back for you.

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I may send it back to Line 6 , I'm just guessing that it will be a lot longer to get it done if I have to ship it to them and back again.  I started a support ticket, but the response was that they didn't know about any such issues even though I sent them a link to this thread.  I'll have to look into time frames and how much it will cost me to rent a mixer while mine is away.

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Hello everyone!




I did fix the issue with dropped volume on the M20D, but after a few months it happened again... it was a cable that was unsold from the rest it was solder again and it worked fine... but I noticed yesterday that the sound from the channels 13-16 is gone... in this case all the line inputs are gone, also.. the Aux input has a very bad quality of sound (it saturates with low or high volume on my iPhone). The headphones jack is also gone... no sound comes from it.


I don't know what could be causing this... any ideas?


What I did:


- Reopened the the M20D casing

- Checked all the cables and connections and everything was OK.

- The M20D recognizes the inputs and assigns the proper icon to the Stage (Line icon)

- Cranked up the volume on the channels to see if probably was a volume issue, it was not. You can see nothing coming on the volume spectrum

- swapped channels with the combi jacks and from 1-12 works fine, no issues there.


So the issue must be something on the 2 sets of line inputs.


Any ideas? This is driving me crazy and there is no more warranty on my mixer ... !



Thanks in advance!



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Did you ask line6 for service?


Check the ribbon cables, on mine it was the fault. Messure every single pin. Repress the IDC conections.

Could be everything else : Missing voltage , broken IC.


nice mixing everyone

M20D Rocks

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I did that yesterday, checked voltages, re pressed the ribbon cables, etc but still is not working.. also the sound from the Aux input when I connect my iPhone is very "crunchy" like it is saturated ... very bad quality.


My main issue here is that the Line 6 service is non existent... we have service from Yamaha distributors here in Mexico. But the service is awful and expensive. I'm getting more frustrated every time this mixer has an issue... it is a little more than a year since I have it and the operation hours that I have used it is less than 500 in sum. I mean what the heck....


I just need to know what could possibly be happening, if anyone of Line 6 Staff could point me in the right direction of what component is in charge of carrying the sound from the line inputs 13-16 and the monitor and main outs (Line6 Link is working fine and also the USB) so I could check that.... that will be awesome!



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  • 3 years later...

My board started doing this a year ago on 2 channels. I thought it was the mics, then compression or a setting. Then cables or receivers. I opened up the m20d and sprayed contact solution on the ribbon connectors and re-seated them. Worked great for about 3 months, now it is doing it again on 4 channels. 3 mic channels and one line in acoustic guitar channel. What to do what to do. 

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This problem will re-occur. Unfortunately the connectors go bad about every 6 months. Get a TF1, the build quality is different league, and it has a load of features Yamaha blatantly "bought" when they took over Line 6!! Only thing missing is the L6 Link, but for the reliability I can live with that.

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  • 6 months later...

Hi !

MASSIVE ISSUES finally addressed here.


bought M20d used from very reputable dealers. Past warranty but line 6 has been willing for me to send it to them. 


However boxing and shipping is not appealing if won’t solve issue in long run.


Main output LEFT  volume SHOWS signal on mixer. BUT no volume comes out virtually brand new Stage Source Line 6 speakers. 


Have tested both speakers . They are NOT the problem.


Left volume does not come out even though display shows signal.


these posts with solutions are old. Can anyone please comment on whether this is still an issue?


also, volume on inputs using various Shure 58 mics is way less than it should be even when a crank gain and volume. 


Mics are not the problem. 


wesonnst are you still there? Anyone?




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  • 3 months later...

It is an ongoing issue for me. I have a client that still hires this mixer and I open it and clean all the ribbon cables and sockets before every hire. This is a 2014 model and it first had the case grounding issue and I did all the mods on post on here way back in time, but still found that the ribbon cable joints oxidise and need cleaning regularly. As I said in my post last March, sell it and get yourself a TF1. Great idea that for me is just not relevant anymore, particularly since Yamaha have no interest in pursuing what is a rival to there range of desks!

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