Open theremin v3 pitch antenna problem

I am super excited I found this forum. I just recently have gotten into learning about theremins and the open theremin seemed like a good project. 

Instead of buying the kit I went ahead and had the PCBs made by a board house so I could get them in white and then I ordered all the components per the V3 BOM posted on the git for the project.

I have assembled 3 of them now as the first I overheated during reflow and thought that might be the cause of my issues. Unfortunatley, all three I have built seems to have the same behavior/issue:
I allowed them to warm up per the instructions and properly grounded it before running the calibration cycle.

The pitch calibration takes a long time and even after it completed it does not respond at all unless I actually touch the antenna. The theremin plays a seemingly random tone that will change if I tap the antenna.

The volume is able to calibrate perfectly without issue and functions normally. 

I am at a bit of a loss as to where to start troubleshooting. 
I have tried 3 boards and two arduinos without a change in behavior. 

Hello tinkeringtanuki,

do have ave an oscilloscope?
Can you measure the frequency of the pitch and volume oscillator?
It should be about 500kHz. Measure it at pin2 and pin12 of U5. The frequency should be more ore less the same as at the output of the reference oscillator U2 and U3 pin7.

gerd

Hello gerd,
Thank you for the help probing the board!
I was able to hook all four test points up to my scope and they were connected as follows:

U5 pin 2 -> channel 1 (yellow)      -  Only drops below 500khz if i actually touch the antenna
U2 pin 7 -> Channel 2 (light blue)  - Steady 500khz
U5 pin 12 -> Channel 3 (Purple)   -   
U3 pin 7 -> Channel 4 (dark blue)   - steady ~460Khz

It would appear that the issue is the 560Khz signal on U5 pin2 is my issue. How do I go about getting that down to where it should be?

I also snapped a pic of the scope while I was at it so I wouldn't have to write everything down:

Thanks again for the help getting me this far.

>U5 pin 2 -> channel 1 (yellow)      -  Only drops below 500khz if i actually touch the antenna
Pin 12 is the PITCH signal!

You have an inductor of 1mH. To achieve 500kHz you need a capacitance of 101pF (http://www.daycounter.com/Calculators/LC-Resonance-Calculator.phtml)
If you measure a frequency of 560kHz, yours is only 80pF.

The total value of C1,C2,C3 (all are in series) is 56pF.
But there is also the capacitance of the varcap D1 (BB914) which increases the total value to 80pF .. 115pF depending on the voltage over C6.

Test, if the varcap D1 works:
Connect the net C6/R3/R4 once to GND and then to VCC. The frequency at pin12 of U5 must jump between 560kHz and 470kHz.

gerd

Hi. I have ordered open theremin v3 pcb and assemblied most of components by jlcpcb. There were only 2 components bb914 and 102jp these i soldered myself. I have same problem as you . My pitch antenna dosles not working. If i touch tje antenna, the tone is changing. The calibratig took about 10 minutes or more for each time i start the theremin. Have you fix the problem?

Hi. I have ordered open theremin v3 pcb and assemblied most of components by jlcpcb. There were only 2 components bb914 and 102jp these i soldered myself. I have same problem as you . My pitch antenna dosles not working. If i touch tje antenna, the tone is changing. The calibratig took about 10 minutes or more for each time i start the theremin. Have you fix the problem?

i have the same problem?do you solve it?

Hi. I have ordered open theremin v3 pcb and assemblied most of components by jlcpcb. There were only 2 components bb914 and 102jp these i soldered myself. I have same problem as you . My pitch antenna dosles not working. If i touch tje antenna, the tone is changing. The calibratig took about 10 minutes or more for each time i start the theremin. Have you fix the problem?i have the same problem?do you solve it?

Yes luckly i solved. As i mentioned i soldered bb914 and some other components by myself. BB914 is really hard to solder. It has micro legs and the pcb pads of this components also very small. I got 5 pcbs.
The first one ; volume antenna worked pitch antenna didnt worked.
The second pcb ; both amtenna didnt work
. 
I soldered missing components for other 3 pcb. This time i paid attention and i soldered carefully the Bb914s more clear than the first and secomd pcbs. The last theree pcbs worked perfectly. After that i removed bad soldered bb914s from first pcb. And soldered a new clear bb914(i didnt soldered the removed one because i thought it may be damaged by heat while removing). I solved it. It started to work perfectly. I didnt remove bb914s from other unworking pcb. But i remove some solder around bb914legs because there were much solder around legs. Finally i saved that pcb too. Now all 5 pcbs working perfectly.the calibrating took 30-40 seconds and everything is good. If you soldered little parts by yourself as me. Check your solder works.

Hello tinkeringtanuki,do have ave an oscilloscope?Can you measure the frequency of the pitch and volume oscillator?It should be about 500kHz. Measure it at pin2 and pin12 of U5. The frequency should be more ore less the same as at the output of the reference oscillator U2 and U3 pin7.gerd

Hallo gerd,

I have almost the same question (I can't control the pitch antenna, the sound only change when I touch the antenna)...but I don't have oscilloscope. Do you know how to test it and find out the reason why it is not working properly? Thank you so much!

Here is the calibration data (you can see that the pitch frequency tuning range seems so strange):

PITCH CALIBRATION

Arudino Freq: 16007308.00

Pitch Set Frequency: 499071
Frequency tuning range: 0 to 0

VOLUME CALIBRATION

Volume Set Frequency: 459854
Frequency tuning range: 441051 to 470092

DAC value L: 0 Freq L: -18800
DAC value H: 4095 Freq H: 10239

DAC value L: 4095 Freq L: 10225
DAC value H: 2652 Freq H: -1959

DAC value L: 2652 Freq L: -1961
DAC value H: 2884 Freq H: 315

DAC value L: 2884 Freq L: 306
DAC value H: 2852 Freq H: 15

DAC value L: 2852 Freq L: -2
DAC value H: 2851 Freq H: 5

CALIBRATION COMPTLETED