Minimum Theremin General Troubleshooting Guide
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If your Minimum Theremin doesn't work, first follow these basic
Make sure that the battery is fresh, and that the red lead of the battery
connector is soldered to the "9V BAT+" point and the black lead to the "BAT-"
point on the circuit board.
Make sure you're using the recommended antenna, (6"-square plate) and
that it is not touching anything except its connecting wire going to the
"ANTENNA" pad on the printed circuit board. The antenna-connecting wire should
not be too long; about 6" to 10" is right. If you have your Minimum Theremin
in a metal box, be sure that the antenna-connecting wire isn't pressed against
any metal surface.
Make sure you adjusted the "ZERO CAL" potentiometer (blue rectangular
part) on the printed circuit exactly as described in Step 25 of the
Make sure your amplifier-speaker system is working correctly. Check
for a faulty connecting cord to the audio amplifier or a problem with the
amplifier, especially if a 60 or 120 Hertz "hum" is evident. If you have
a different amplifier and connecting cord available, we recommend that you
try them for comparison.
Poor fidelity may be caused by interference from a nearby source such
as a fluorescent lamp, computer monitor, or appliance. You can determine
if the problem is being caused by interference by moving your theremin to
another location, away from electrical devices, and seeing if there is an
Next, look at the circuit board:
Verify that all the parts are in their correct positions.
Verify that the POLARIZED parts (C5, C6, C7, C8, CR1, CR2, CR3, U1,
U2, VR1) aren't put in backwards.
Make sure all 14 pins of each U1 and U2 have been pushed through the
Make sure that none of the wire leads have broken off their component
bodies, and that none of the components look excessively discolored or charred
from too much soldering heat.
Make sure that none of the conductive traces on the printed circuit
board have been burned away by excessive heat or abrasion from
Check the kind of solder you used, and make sure that it is one of the
recommended types, or equivalent, to those described in Step 2 of the
Assembly Instructions. Improper
solders may leave a conductive residue that prevent correct
Look at all the soldered connections carefully with a magnifier, under
a bright lamp, to make sure there aren't any fractured solder joints or "solder
bridges" between adjacent points. This may happen where points are close
together, such as with U1 and U2, or the two closely-spaced points for
electrolytic capacitors C5, C6, C7, or C8.
Large "globs" or "peaks" of solder on a connection may hide the fact
that the solder has not adhered to both the protruding component lead and
the board's conductive pad. Good solder joints will have a thin application
of smooth solder that conforms to the contour of the component lead and flows
smoothly onto the pad. The contour of the component lead should be clearly
visible under the solder, and there should be no "voids," or little air holes,
in the connection. For conventional tin-lead alloy solders, the connection
should have a bright, smooth appearance with no cracking. The appearance
of connections made with lead free (tin) solders will have a duller, somewhat
coarser appearance, but should otherwise have similar characteristics to
connections made with tin-lead solder.
Improper soldering, especially the application of too much heat, may
result in the discoloring of the solder pad's surface and/or the component
lead. In such a case, the solder, itself, may also look dull and have a darkened,
charred appearance. This discoloring results from oxides on the metal surfaces,
and may prevent a good electrical connection between the component lead and
the circuit board pad. If such discoloring is evident, then it is advised
that all the solder is removed from the connection with
or a vacuum desoldering tool. Then
the metal surfaces should be gently scraped so that the oxidized surface
is removed, and fresh metal is exposed. This may be done with a fine-blade
hobby ("X-ACTO®") knife, however, take care not to completely sever the
thin metal traces that connect to the pad. Once the pad and lead are cleaned,
the connection may be resoldered.
Inspect the top (component side) of the board
for solder globs between adjacent leads, especially the close-spaced leads
of U1, U2, and VR1. Such excess solder may cause short-circuits, and must
be removed with solder wick.
Note that almost all problems with the Minimum Theremin result
from improper soldering.
Next, look at the connections between the circuit board and the parts
external to the board:
Make sure the wires to the output jack are not accidentally reversed.
Make sure that the ON-OFF switch is properly connected. One of the wires
to the ON-OFF switch should go to to its center terminal.
Make sure that the three wires to the ZERO potentiometer are connected
If your Minimum Theremin still doesn't work, please
contact us for