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

12 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.

    ReplyDelete
    Replies
    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.

      Delete
  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

    ReplyDelete
    Replies
    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

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

      Delete
    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.

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

    ReplyDelete
    Replies
    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.

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

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

      Delete