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 Stuck on Theremax 
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Joined: Mon Aug 27, 2012 2:24 pm
Posts: 2
Post Stuck on Theremax
Hey all,

I'll start this by saying I'm a novice when it comes to electronics.

I recently completed construction on my theremax theremin with a custom case (I used a plastic shoebox purchased from the container store with aluminum foil as a conductive bottom panel, per Scott's advice). I went through the basic testing phases, checking all of my connections and solder joints (they looked mostly ok, though there were two spots where the platforms for the solder joints were so close together they already appeared to put touching, in these instances the joints might not be sound), plugging it in, turning it on (the light came on!), waiting for smoke, etc. etc. When I went to plug it in, no sound other than the plug going in. As I attempted to tune the oscillator coils, I could not get them in a range that would turn the Gate/trig light on, which led me to assume that I wasn't getting power there.

I got a multimeter and tested it on the Ohm setting and it works, but when I turn it to DCV 10 or DCV 50, with the negative lead on the ground (which at this point is no longer screwed onto the circuit board, I'm not sure if that makes a difference), I can't get a good reading on anything. The only thing that got even a mild reaction was after I initially turned it off I could get a reading from the ground to the switch.

Any thoughts?

Sat Mar 02, 2013 4:43 pm
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 733
Post Re: Stuck on Theremax
If the panel Power LED lights when you switch on, the power must be getting to the LED. Maybe one of the two power supply wires doesn't have a good connection with the board.

The plus pole of the DC power supply is directly connected to one end of the the power switch. The wire to the "+" wiring point on the printed circuit board, and, the Power indicator LED, connect to the middle terminal of this switch. When the lever is up the board and LED contact with power.

You should be able to get a voltage measurement touching the power supply minus pole and the lower terminal of the Power Switch when the wall-mounted power source is plugged-in (14-17 V DC when Off and 12 V DC when On).

There are separate circuits for the Power LED and the pcb: The LED gets voltage from the middle switch terminal's contact with the power supply when the lever is up and the "ground/circuit-common/0_V_DC" via resistor R77 and its connection with a wire on the upper terminal of the power switch that runs to the solder lug serving as a tie point for it and the the power supply minus-pole. The pcb also gets voltage from the power supply via the middle switch terminal and wire "+". Wire "G" connects the board to the minus tie point.

If there isn't a good connection with the pcb and the power supply via wires "+" or "G", the LED would show power, but the board not be getting it.

Inspect to be sure the solder flowed to all the wires in the power supply minus tie-point, the center Power Switch terminal, and at the pcb solder joints for wires "+" and "G".

Once the power to the board trouble has been resolved, and, if you don't get the expected results, have a look at the topics including the trouble-shooting tips/suggestions over in the Theremax section in the Technical Bulletins and Assembly Notes area of the forum:


Scott Lee

Mon Mar 18, 2013 3:52 pm
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