7
•
Are the components of this circuit soldered and installed correctly? Check R27, R28,
R29, Q3, C18, C17, R33. Make sure that Q3 and C18 are not reversed, and the pads
of C17 and C18 are not bridged.
APENDIX A: IF ONE OF THE 2 SIDES IS NOT WORKING (EITHER HIGH OR LOW)
•
Make a tiny incision in the heat shrink of the optocoupler (on the side that isn’t working). Use your
X-acto knife to slice open about 1mm of the back side of the optocoupler’s LED (near the LED’s
leads). The incision just needs to be big enough to see if the LED is lighting up when the DEPTH
knob is fully counter clockwise. When you’re done with this step, cover up the incision again with
something opaque, like fingernail polish, opaque hot glue, or even sticky-tack (poster putty)....just
something to keep out the light.
a. If the optocoupler’s LED is NOT lighting up then you know the problem is with the
digital part of the circuit.
i. Check to make sure Q1 and Q2 are soldered and installed properly. Also check
the solder joints on R7, R8, R13, R14, VR8, VR9, and, of course, the LED side of
the optocouplers.
ii. Check for 5V on R7 and R8 (note the PCB voltage graphic above).
iii. Check for around 1.8V on the square pad of the square pad of the optocouplers.
iv. Is the optocoupler LED in backwards? Check this with your meter’s diode tester.
With the red probe on the LED’s square pad and the black probe on the round pad,
the meter should read around 1.8V (which is the forward voltage drop of the LED).
If it does not read around 1.8V then reverse the probes and check again. If it gives
a reading of 1.8V with the probes reversed, it means the optocoupler is in upside
down.
v. Is there a problem with the trim pot (VR9 or VR8)? With the POWER OFF, measure
the resistance between the red pad (on the PCB voltage graphic) of R7 or R8 (the
resistor on the side that is not working) and the square pad of the optocoupler; it
should be less than 10K ohms (most of the time, much less). When you adjust the trim
pot, you should notice this resistance changing. If you can’t adjust this resistance,
then you may have a problem with the trim pot. Try the “wiggle” test next...
vi. Turn the pedal on in calibration mode while the pedal is plugged into the guitar
and amp. Turn the HARMONIC MIX KNOB to the side that’s not working, set the
DEPTH KNOB fully counter clockwise. As you strum the guitar, very, very gently
wiggle the trim pot on the side that’s not working. Does the signal jump or fade
in? If so, make sure the bottom trim pot is firmly seated against the PCB...Re-solder
it if necessary. See if that helps. If not then you’ll need to replace the trim pot.
Summary of Contents for QUAK
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