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
- put a 1k resistor (or shortcut) pin 2 of X28 to pin 13 of X29, to put 5v on the 4053 ABC circuit control
- pin 2 of x28 connected to pin 20 of x28, to put ABC of IC8 high, and bypass the dsp board insert signal
- 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
- optional: connect a mono jack to the new switch selector to use an external pedal for channel selection
- put damaged dsp in litter basket :)
hope it will help someone
- sorry for my poor english
- read risk disclaimer