May 2004: Just returned from Loopstock 2004, testing my rig, I realize pressing the button "Program" does not work anymore. Neither does the top row of buttons: "Gain", "Effect 1", "Effect 2".
Oops! Had just bought this puppy off eBay!
Ok, first test: Using the footpedal MPX R1: From here, everything still works.
This means: The fault must sit in the frontpanel.
I unscrew everything, realizing someone already had opened this thingy before! Can't trust those eBayers... and I realize that you can't trust the printed circuit board, either. E.g., what is called "Program" on the front panel (left) is called "Play" on the circuit board (right):
... "Effect 2" on the front panel is "EQ" on the circuit board...
The first attempt to fix is to use some contact spray to clean the buttons...
...to no avail. Sigh!
Oh... but then... isn't that a broken diode ?!
Unsolder the culprit...
Get a SMD diode replacement. Strange... this one has 3 legs, I always thought diodes had 2?! I test which of the three legs represent what I understand is a diode... and solder it in.
And off you go. Easy as pot! (Or rather... beginner's luck!)
How the diode could break behind this solid looking frontpanel remains a mystery...
November 2004: Returning from Y2K4 I realize again, that some buttons, including the quite important "Tap" button is not working. And the culprit again is a broken diode. So I apply the same procedure, successfully. And I believe, the thing that keeps breaking those diodes is the big round knob used primarily for selecting programs. It gets pretty close to those tiny glass diodes.
In order to remove this knob, the frontpanel must be removed, which takes some time. So I just cut off the border that kept it behind the frontpanel with a blade cutter, and now I can just remove the cap before packing things up. I hope this will fix the problem with breaking diodes...