DOD FX-90 delay - no self oscillation - Help please?

[Elvis Cocho]

Hi. I recently acquired an old DOD FX-90 analog delay. It was in need of repair and I was able to get it going again. I replaced a broken mic control with a matching 100k pot and I replaced the dc power jack with a modern one. I don't need battery power, so I removed the battery snap.

Now that I have it working, I can't get the repeats high enough for my taste. I have the repeats knob dimed but I can't get it to self oscillate at any delay time setting. There is a 2k2 trimmer near the BBD that has effect on the repeats. If I twist to the left, repeats disappear. I have it all the way up and the repeats are just kind of weak.

The clock trimmer is set correctly with around 160us clock period. There's a 50k trimmer next to the compander chip that pretty much operates at a sweet spot. Any twisting to the left or right will cancel any repeats.

Can anyone give me some advice on what part of the circuit I should be looking at to help strengthen the repeats of my delay? The component values on my pedal don't exactly match what the schematic lists, so I'm sure there's some spec part or value I should be looking at. I greatly appreciate some advice. I'll post schematic as well. Hopefully it doesn't appear too small.  Thank you!

[bean]

IIRC, the FX90 does not naturally go into self oscillation. You can induce it by lowering the 22k resistor off the Repeat pot (the one that goes to pin12 of the NE570) to 15k or lower. At least that's what I did on my clone.

It wouldn't hurt to audio probe the output of the expander section of the NE570 and the two de-emphasis filters (TR4 and TR5) to make sure you aren't losing the delay level throughout as well.

[Elvis Cocho]

Thank you so much for the advice! I mistakenly posted about this topic twice. Hopefully I can delete the other post.

[Elvis Cocho]

Thank you so much for the simple and elegant solution. There was a 20k resistor behind a .56uF electrolytic capacitor that went to pin 2 of the repeats knob. I changed it to a 12k and now I get self oscillation. Problem solved. Thank you!!