Tuesday, January 3, 2012

Behringer v-tone GMX212 repair - bypass the dsp board

-- ref. 2011-07 --

I've buy a damaged behringer v-tone gmx212 guitar amplifier for a few euros.


The dsp fx board was damaged, sometimes it display the "d2" error, sometimes just make the audio signal buzz, or do not work nothing. Voltages seams ok, ic and components seams all ok and the dsp.
I've scope around but i can not find anything wronk (i'm a software developer with electronics hobby, i'm not a pro here), so i've decided to remove this board and bypass the dsp.
The dsp board control the signal path, using the two 4053, IC8 to control "insert" signal, IC9 to control channel 1/2 selection.
to remove the dsp board we have to control the 4053.

IC8 must let the signal flow from pin 4 to 3, and from 14 to 13, because i want to bypass the dsp.
IC7 must let the signal flow according to a channel selection.

It should be pin24_x28 to switch to pin7_x27. Let me know if it works

Solution steps:
  1. put a 1k resistor (or shortcut) pin 2 of X28 to pin 13 of X29, to put 5v on the 4053 ABC circuit control
  2. pin 2 of x28 connected to pin 20 of x28, to put ABC of IC8 high, and bypass the dsp board insert signal
  3. pin 24 of x28 connected to pin 7 of X27 (which is the ground), or disconnected from ground to select channel 1 or 2, i've used a switch and removed the sw9 to use the sw9 hole
  4. optional: connect a mono jack to the new switch selector to use an external pedal for channel selection
  5. put damaged dsp in litter basket :)

hope it will help someone

notes
  • sorry for my poor english
  • read risk disclaimer

schematics

pictures

42 comments:

  1. i just want to say thank you. i got this amp back in high school as a gift and it stopped working properly shortly after the warranty expired. its been collecting dust with a D2 error for almost 10 years and your blog post has given it new life.

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    1. Thank you for your comment. I will post soon a mod to this amp. I've replaced the preamp board, i mean all the long board with pots, with a pre amp built over a 12AX7 that I have here doing nothing. A PT2399 gives some sort of delay effect to that. The multioutput board on the back of this amp, and the amp board was not touched by this mod.

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  2. Hello i'm trying to make this alteratiin to my gmx1200h but o ran in to some things that are not acurate such as:
    1. U say to make the conetions on x 27 and in the picture is X 28
    2. U say to use the pin 13 to the pin 20 and by the photo it seems the 19.
    And the switch u dont say wat type of switch it is.
    Can u help me

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    1. Hello, an SPST switch would do the job. I may do typo error in this description, please let me know what number of pin I've to fix. It should be pin2_x28 to pin20_x28, pin2_X28 to 1kR to pin13_x29, pin24_x28 to switch to pin7_x27. Let me know if it works. Anyway, my board now is disconnected, it has been replaced by a custom preamp tube board: https://davidegironi.blogspot.it/2016/04/behringer-v-tone-gmx212-hybrid-tube.html

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    2. One more thing after this alteration the fx dont work any more rigth?

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    3. Hello. This mod skip the FX boad, I've developed this because my FX board does not work. You have to take your FX board out in order to make this mod work.

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  3. Well its good to hear my amp again tank u Davide from azores a hug.

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    1. Thank you for this feedback! So, just for the other people, is the last wiring i write the correct one, if so i will change this post description? I mean: pin2_x28 to pin20_x28, pin2_X28 to 1kR to pin13_x29, pin24_x28 to switch to pin7_x27.

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    2. Yes it was rigth, and a litle advose try to use the smalest switch u can find to use for channel

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    3. Thank you, I've updated this blog post.

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  4. Thanks very much. It works for my 💀 death amp.
    I do follow the steps and support by pictures. Goes perfectly fine.

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  5. This comment has been removed by a blog administrator.

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  6. I have a question. I bought vtone gm 212 and its missing the input jack and I put circuit boards. Where can I buy one or how do I bypass it ?

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    1. Hello Travis71, i do not know where you can buy one, I'd ask Behringer support about this. What you can do, instead is build it. You can buy parts from electronic store or ebay. What you have to build is the top left part of the schematics (look at the schematics pdf in this page), then one with R105, R106, R144, R56, R57, C51, C50, C118, C53 and T2. It's a simple JFet guitar amplifier, like this one http://www.till.com/articles/GuitarPreamp/ you can even replace that circuiti with the Tillman one. Hope this helps.

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  7. Im so sorry I really am a beginner at this. So I need the input jack mine did not come with one so will I have to wire a jack to the 4pin just connector? Or how do I achieve what im trying to do which is be able to plug in my guitar and be able to use the effects.

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    1. Hello Travis71, if you want to use just the effects I thing more rewiring is needed. That will not be a beginner task.

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    2. No i mean i want to get it like it is when you first buy one . You know plug up your guitar and you can go through all the diff effects it has. . well my amp is missing the input jack i don't know if there was any board missing , all I see is the board next to where the input jack should be and i see a jst connected with nothing plugged in it so I assumed the input jack goes there but how?

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    3. Hello Travis71, as I tell you, you can build this board with just a few components, look at my comment here: March 27, 2020 at 2:17 PM. You can also skip this board, and do the connections like my comment here April 15, 2020 at 6:27 PM, it will sound just with a lower volume, but it will sound. Also you can contact the Behringer support, they can sell you the replacement part.

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  8. And how what do I connect the input jack to . if you could use the most simple explanations possible if appreciate it .

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    1. Hello Travis71, you have to connect the input jack GND to port X26-pin3, and output to port X26-pin2. Note that X26-pin1 is VCC, it may damage the device connected to the input, so leave this pin unconnected.

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    2. And doing it this way the effects will still work
      ?

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    3. Hello Travis71, if you do this the right way, and this is the only damaged board yes.

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  9. I won't need any capacitors or anything?

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  10. Ok so it's not the Department board I need I am trying to put a input it jack in it but don't know where it connects to . can you I help with that?

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    1. Dear Travis71, please stop flooding with the same question. See my post here: Davide Gironi March 27, 2020 at 2:17 PM

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    2. It's not the same question you've told me how to bypass dap board i need to install input jack

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    3. I've told you how to install the input jack, look at Davide Gironi March 27, 2020 at 2:17 PM (top left part of the schematics... is the input jack, not the DSP).

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  11. It works perfect!! and keep the drive for each channel. Thanks a lot, maybe make mi own pre-amp later too!

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  12. Whew!!! Ok , being a total beginner I finally got it!!!!yeah. I have bypassed the dsp and wired a input jack directly in! I'm very proud of myself. But my fx aren't working ,any suggestions?

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    1. Happy yo hear that. Unluckily of your fx board Is not working It probably due to the DSP chip, in this case you have to call the beheringer support.

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  13. Hi, i just want to clone this amp, can you help me with Ribbon connections?
    i know x6 go to x27, i don't understand so much gmx212 schematic

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    1. Hello AlreadyinDrug, Unluckily I do not have the time to backtrace the schematics for all the ribbons, if you want ask me a couple you have doubt on, I will check it.

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  14. Davide, I followed your directions, but I can't see exactly which pins you used for the input jack. I will be using a mono jack and a foot switch. Can you tell me which pins are for the sleeve and tip on the input jack. Thanks.

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    1. Hello, you can find the pin in the schematics. It's a bit complex to read those, but it's all there. At present I've modded the amp, it's now became a pre/valve amp (http://davidegironi.blogspot.com/2016/04/behringer-v-tone-gmx212-hybrid-tube.html), I've searched for the board to make further pictures but I can not find it anymore.

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