WMD Geiger Counter hash

[Mick Bailey]

I have a WMD Geiger counter in for repair – the Wave Table rotary selector had been hit and broken off the PCB (now fixed and working) but there’s a remaining fault in that there’s an overwhelming amount of digital hash accompanying each note. The owner tells me this was the main problem prior the physical damage to the selector.

It looks like there’s a fault that’s causing a random noise source within the unit and this is getting processed along with the guitar signal.

Does anyone have a schematic for this pedal? Maybe there's limited scope for repair if there's a firmware or DSP fault, but if there's something going in with the signal prep or A/D conversion it could be a case of an off-the-shelf component swap. It's not an easy board to 'read' due to pots being soldered over the DSP and also obscuring large areas of the board.

[Enzo]

If it is digital sounding hash that only accompanies the notes (as opposed to noise that is there regardless of notes), my first thought is a missing bit or two in the data buss. And often as not that is from a failed solder joint on one of the LSIs.

[Mick Bailey]

That's right - the noise only accompanies the notes. My first thought when I got the pedal was "how do I know if this is broken?" It's a bit-crusher and only fully appreciated the problem after listening to a few clips of a working pedal. It can get pretty abstract and extreme.

I'll take another look at it later today to see if there's a solder problem. I did look over the board under magnification and couldn't see anthing obvious, but maybe it needs a 'woman's look' as my parner calls it. Especially when I can't find my keys and they're right in front of me.

I also had a very kind reply from William Mathewson (the WM in 'WMD') offering to repair the pedal.

Edit: Just had a much closer look and the main processor is niceley soldered, though I did reflow it just to make sure. No change. There are 256 wavetable locations and I went through each one in turn. Many in the upper locations just have a gated hash and no musicality whatsoever - the pedal output has no note-related content with those patches. Each 'dead' patch sounds identical, though the waveform lookup suggests that there should be a significant difference. The patches that do work (to some degree) have extreme variation in volume and the controls also behave unpredictably.

There's a program header on the board - perhaps the DSP can be interrogated or rewritten but then again this means access to the code, so maybe this is one for the factory to look at.