Need some help LFO trimming (scope photos included)

[koenpepping]

Hi,

I am trying to trim my yusynth LFO, but it doesn't seem to work really well. (scope y is divided by 5v)

I've tried a lot but:

The LED is always on, it doesn't blink

The triangle looks more like a saw

Pulsewidth is varies from 0% to 10% (as you can see on the picture)

Sine doesn't really look like a sine (see picture)

what can i do?

thanks!

---

IMAG0928.jpg
Description:	Saw
Filesize:	600.81 KB
Viewed:	696 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

---

IMAG0927.jpg
Description:	Triangle
Filesize:	751.63 KB
Viewed:	609 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

---

IMAG0926.jpg
Description:	Sine
Filesize:	764.39 KB
Viewed:	624 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

---

IMAG0925.jpg
Description:	Pulse (on maximum pulsewidth, minimum is just a flat line)
Filesize:	763.17 KB
Viewed:	589 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[Andrej]

hi everyone.

I know this topic is old, but same problems remain. i've got the same trimming problems. and my LFO2 oscillates at very high frequency, just like VCO. I used ICM7555 , TL071 and TL074. all parts were checked before soldering and all voltages are ok.

any help please?

[yusynth]

Are you sure you used a BC557 (PNP) for Q1 ?

For your scope shot what is the amplitude (V/square) and time scale (ms/square) ?

[RyBowk]

I have the exact same issues as this, does anyone know the solutions at all yet? I have replaced all ic’s, transistors, caps. No change. My scope images are exactly the same as these. I am powering at 12v by the way many thanks Ryan