Calibration Procedure; Troubleshooting - 4ms Quad Clock Distributor Expander Builder's Manual

Calibration Procedure

Calibration is completely optional. The only reason to spend time calibrating is if you require more
precise duty cycles and Div/Mult CV response. There are natural variations in the resistance value of the
potentiometers when they are set to the center detent position. The calibration procedure compensates
for these variations. Again, its completely optional and should only be performed once the unit is
verified working 100%. Calibration should only be preformed by advanced electronics people
comfortable with soldering, making resistance measurements (never in-circuit!) and measuring things
like duty cycle and frequency.
If you notice that any of the potentiometers are not centered in value when physically centered, you can
adjust them by soldering resistors across their pins. For instance, if the duty cycle is 60% when the Gate
PW knob is centered, you may optionally change this to 50% by soldering a large value resistor between
lugs 1 and 2 of the Gate PW pot. If it was 40% when you wanted 50%, then solder the resistor to lugs 2
and 3.
For the resistor value, start by trying a value of 1M, then try 680k, 470k, 330k, 220k, and 100k. If the
issue gets worse when you solder a resistor on, then you soldered to the wrong lugs (ie 1 and 2 instead of
2 and 3). You could also solder two lugs of a 1M pot to the Gate PW pot and adjust the pot until you get
the expected response. Then remove the pot, measure its value, and replace with a resistor of the same
value. Another approach is to solder trimpots

Troubleshooting

If something in the testing section isn't working, continue the entire test procedure and take notes of
what doesn't work.
1. Verify all ICs are correctly orientated.
2. No LEDs turned on? Make sure you turned the LED dimmer trimpot to center. Still no LEDs?
Verify if you have a pulse wave output on the INV OUT jacks. If so, then the module is working
and perhaps you just put the LEDs in backwards.
3. No LEDs and no output from INV OUT jacks? See if the Div/Mult CV attenuator pots work.
Patch CV into the QCD's Div/Mult CV jack and see if adjusting the attenuator on the Expander
changes the response in frequency to the incoming CV. If so, then the Div/Mult CV attenuation
section is working, but the Pulse Width section is not working. A likely culprit is something on or
around the ATTINY2313 IC
4. If one or more channels doesn't work, but at least one channel does work, then you can rule out a
bad ATTINY2313 chip.
5. If a switch doesn't seem to work, verify the pins are actually going through the PCB.
6. Check for bad joints. The number one cause of problems is bad solder joints. Even experienced
kit builders miss a pin, or short two pins together. Take 5-10 minutes right now to inspect each
and every joint. Remove the faceplate if necessary. When you're done, if you still have problems,
a good procedure is to re-flow each joint. This forces you to visually inspect the joints. It often
results in the unit "magically" working!
7. Check for component errors. The number two cause of problems is wrong components in the
wrong place, or backwards components. Backwards chip? Backwards diode? Check again, it's
easy to do! IC socket pins have a tendency to bend under rather than go into the hole, so check
all the pins on the socket went through the PCB, and that the pins on the IC itself went into the
socket.
8. Note: While an easy scapegoat, it's extremely rare for the cause of problem to be a bad
component. Resistors, caps, and diodes are very very rarely damaged without obvious visible
evidence (ie, they look like burnt toast). However, ATTINY chips can get zapped. Make sure to
install this chip last, and keep in ant-static bag and foam until used.
9. Measure voltages on the chips:
1. Set the voltmeter to measure DC voltage (not AC).
2. Hold the black lead of the voltmeter to ground. An easy place to find ground is the large tab
on the 7805.
3. Verify the voltages:
ATTINY2313: Pins 1 and 20 = +5V; Pin 10 = 0V (ground)
7805: Pin closest to center of board=+11.6V; Middle pin=0V, Pin closest to edge of board=+5V
TL072 (all seven ICs): Pin 8 = +11.6V; Pin 4 = -11.6V
(Google "IC pin numbering" if you don't know how to count IC pins!)
10. If something got hot when you powered up (especially the 7805), remove all the ICs from the
sockets before powering up again. Then see if the 7805 is still getting hot. If it is, check for
shorts anywhere on the board. If it's not getting hot, insert the ICs one at a time and see which
one makes it start getting hot.
Don't give up!!