PHOBOS GERMANIUM FUZZ
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TROUBLESHOOTING INFORMATION
What happens if you finish building the kit and find that it doesn’t work right? Here are a few common
problems people have with this pedal and how to solve them.
The LED doesn’t light up.
First, does the pedal sound right? If you aren’t getting any sound, you probably have a power issue with
the whole circuit that is not specific to the LED, so you’ll want to look elsewhere for the problem.
If it does pass a signal, it’s probably just the LED itself. Is the flat side facing to the right (looking in the
enclosure from the back)? If it’s reversed, it won’t work, so you’ll have to re-solder it the right way.
The transistors won’t bias correctly.
If you can’t get the right voltages on the transistors, there are a few steps to diagnose the issue.
Is the charge pump putting out the correct voltage?
The charge pump (IC1) is an inverter that co9V to -9V so the circuit can be used with a standard
center-negative power supply. If it’s not inverting properly, nothing else will work.
First, set your multimeter to DC mode with a range of 20V or higher. Touch the black lead to a ground
point for the circuit. The easiest spot is inside a tapped screw hole in one of the corners of the enclosure.
This way the probe stays in place without needing to use alligator clips. The circuit must of course be
fully installed in the enclosure for this to work.
Then, touch the red probe to the lower-right pin of IC1 (pin 5) and read the voltage. Note
that IC pins are labeled counter-clockwise from the upper-left, as shown in the diagram to
the right. It should measure the inverse of the supply voltage, or slightly less.
If the voltage is not -9V, then there’s an issue with the charge pump itself or the surrounding parts.
Are the transistors touching each other, the side of the enclosure, or any other nearby component?
Some transistors have the metal case connected to one of the pins, so anything making contact with the
transistor will interfere with its operation. Make sure the transistors are angled away from each other
and away from the side of the enclosure, and that they don’t make contact with the underside of the lid
when it’s closed.
The voltages are close, but not exact.
Is the collector voltage correct? The other voltages are given as rough guidelines, but they may be
slightly different depending on the properties of the transistor. The collector voltage is the one we’re
concerned with. If it’s right, then the others should be OK!
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