Hi all!
I've built this oscillator on a bread board, and it worked fine!
But when i transferred it to a perf board i got a problem as you can se in the picture. And it's a pretty annoying problem since four other wave shapes is modified from this triangle wave...!

I've read about that the jfet's on resistance can cause this, but it's the same one that was on the bread board so.. what's happening?

Any tips?

Thank you!

 

Looks like the trip point of U2B changed, did you swap setpoint Rs by accident ?

Regards, Dana.

 

Yeah that's what I've been wondering about that to!
Rs?
All of the resistors around U2B seems to be the correct value.
Any specific resistor in the circuit you can point to?

Thank you!

 

R46, 47, 42,69

Regards, Dana.

 

R46, 47, 42,69

Regards, Dana.

No they all seem to be the correct value.
But as you say it feels like there is something wrong with the triggering point..

 

Obviously the integrating cap is not being discharged long enough,
and its clear its being switched properly in that the ramp abruptly
changes, no tailing off or exponential discharge.

Post a pick of ramp and comparator out, and if possible ground reference
on scope, in relationship to waveforms.

Regards, Dana.

 

For a moment I thought I had it figured out, but as it turned out I didn't..!
I've done some simulations trying to figure out what is going on.
As I was messing about with I screwdriver to see if there was a connection between any of the copper rails the problem got a lot better! and I don't know why! So, for now, the problem is solved but I don't know how...
Now the frequency range is a bit off, it goes very very low and not as high as i would like it to. So it's back to the simulation to what can be done.

Thank you danadak for your help! I will take a picture and post!

 

Obviously the integrating cap is not being discharged long enough,
and its clear its being switched properly in that the ramp abruptly
changes, no tailing off or exponential discharge.

Post a pick of ramp and comparator out, and if possible ground reference
on scope, in relationship to waveforms.

Regards, Dana.

There is something strange going on... The frequency has increased a bit, but as the top frequency is climbing the problem is returning and getting worse.
But no modifications have been done to the circuit.
I have a problem with my other scope probe so I can't take the picture right now.

 

Sure sounds like a floating/loosly coupled connection, a little heat,
a little stress and its connection integrity suffering.

Do you have any cooling spray in a can, move over circuit section/part at a time
and cool it to see if there is a big sensitive part/connection.

Regards, Dana.

 

Ha! It's solved!
It was C18 that was 4,7nF instead of 4,7pF!