Boss DM-2 trimpot adjustment.
Instructions are at the web site below, but this is to
further explain:
http://www.godiksennet.com/images/sch/DM2PG2.jpg
You will need a scope (no way around it) and a 200Hz
test tone (I generated mine out of my computer sound card).
STEP 1
Take the base off the pedal and swing the board out.
Identify TP-1 (written on the board), VR1, VR2 and VR3.
STEP 2
Hook the scope up to TP-1 (with the ground clip of
the scope clipped to the metal pedal body. Plug a lead into the input - but
don't plug the other end of the lead in (this is only so the pedal will turn
on). Plug the ASA adapter into the pedal if you are using one. Turn the pedal
on. The clock signal is "free running" - it doesn't need an input
signal to be there. On the scope, set the sweep to 50 micro-seconds/division,
and volts per division to 2. Check that you can see a clean square wave. Don't
worry about the service note that says "power supply 8V". Make sure
the pedal knobs are set to fully counterclockwise
(e.g. set to "minimum"). Adjust VR-3 until the square wave you see
("T" in the service notes) is just less than 3 divisions on the
scope. That's it.
STEP 3
Put a 200Hz sine-wave tone into the input of the pedal (I
just used a test tone WAV file I made using cool edit, sent out of my laptop's
sound card). Check the "size" of the tone with the scope - the input
is at terminal 3 of the circuit board. Make sure the signal is about 300 milli-volts peak-to-peak. Hook the scope up to terminal 7
on the circuit board (purple wire on my DM-2). Set the scope to 3
milliseconds/division and volts per division to 0.5 Set
the pedal knobs to "off" (maximum counterclockwise).
You may not see anything but a flat line on the scope at this point. Turn VR-1
until you see a sine-wave appear. Adjust the volts/division on the scope until
it fills the screen on the scope. Now carefully adjust VR-1 until the waveform
on the scope is as pure a sine wave as it can be, with the maximum amplitude
you can get - a smooth wave is what you are looking for (it won't be exactly
perfect, but it will be close). That's it.
STEP 4
Leave everything as it was for Step 3, but set the
scope input to "AC" and change the volts/division to 0.1. Touch the
scope probe to the wiper of VR-2 (of the 3 solder pads for VR-2, it's the one
closest to the NE570 chip). You should see what appears
to be two strange waveforms. When you adjust VR-2, the waveforms will move
"closer together" or "further apart". Adjust VR-2 until the
two waveforms sit exactly on top of each other. That's it. Close up the pedal,
you are done.
I've just looked at
the schematic for the DM-3 and from a trim-pot setting perspective,
it appears to be identical to the DM-2:
- in step (2) you would adjust RT-3 in the DM-3. I'm
not sure if "TP-1" exists in a DM-3, if not the signal you want is on
pin 4 of the 3102 IC.
- in step (3) you would adjust RT-1 in the DM-3
- in step (4) you would adjust RT-2 in the DM-3