Problem tuning cymbal - no square wave from R44*

Everything on the Cymbal is soldered and it's time for tuning. Unfortunately I don't get a square wave from R44* The wave looks like this

As you can see the oscilloscope threshold is really low compared to the setting on R45 (pic below), and what I'm actually seeing mey be just noise basically. Turning the trimmer doesn't do much to the wave. Everything should be soldered OK. Any idea where I should start looking for the cause of the problem?

On R45* everything went just like it should, the only little setback was that I had to change the resistor from 100K to 68K, but after that I was able to trim the wave length to 1.2 ms. Picture of that.

Also the voltages start to wander off. On U3 I get 14.36 and -14.69 but on U5 the readings are 13.96 and -14.12. What can I do to fix this?

I noticed the period in your first screenshot is much shorter than your second. I just tried tuning TM1* & TM2* and I get a strong 50Hz wave along with the square wave on both R44* and R45*.
Could you check if you have the same problem on R44*? You need a time window of more than 20ms to see the 50Hz wave.

Also, how do I get rid of it??

ElSchtroumpf wrote:I noticed the period in your first screenshot is much shorter than your second. I just tried tuning TM1* & TM2* and I get a strong 50Hz wave along with the square wave on both R44* and R45*.
Could you check if you have the same problem on R44*? You need a time window of more than 20ms to see the 50Hz wave.

Also, how do I get rid of it??

I checked but don't have that kind of problem. On a longer time frame my R44* looks like this but as I said, the threshold is so low that the wave is mostly noise I guess. The actual square wave I should be seeing is missing I think.

Hi Gyuunduh,

Are you grounding your scope to pin 7 of U1?
I had a similar problem and it was due to not grounding the scope properly.

lfo2vco wrote:Hi Gyuunduh,

Are you grounding your scope to pin 7 of U1?
I had a similar problem and it was due to not grounding the scope properly.

On previous tests I have had it grounded to the main ground connector GND that has a direct connection to pin 7 of U1. That way I have gotten the correct waveform from R45* which should mean that the problem is not in the grounding of the probe. Now I tried also from pin 7 of U1, but the waveforms are the same as previously, as they should be. So no help from there, but thank you anyway.

Vincent, where are you? I need your help!

I figured out how to ground my scope (I'm not using the sound card scope but a USb scope) and got both square waves sorted out. Had to change out both R44* and R45* though.

I'm probably stating the obvious but have you checked this thread? viewtopic.php?f=16&t=209&start=10

ElSchtroumpf wrote:I figured out how to ground my scope (I'm not using the sound card scope but a USb scope) and got both square waves sorted out. Had to change out both R44* and R45* though.

I'm probably stating the obvious but have you checked this thread? viewtopic.php?f=16&t=209&start=10

I had not noticed that thread, thanks for pointing that out. I checked the waves from different pins of U1 and got nice square waves from pins 2 to 10 but 12 gives me a same looking false shape as R44*

So what am I to do?

Pin 12:

R44*