EHX Small stone v4 turned into a air raid siren

[GorillaHuman]

Pulled out the good old phaser I got, an EHX small stone. Played it, nothing wrong... until I switched it to color mode. Almost **** my pants; some sirene went off. It could be varied with the rate-knob. So, up it goes onto the workbench! Thought it would be a blown OTA or tranny, but none of that. I desoldered the trannies in the feedback (color) section as well as checking the capacitors using my component-tester. Nothing turned out to be defective. The way I understand the circuit is that the feedback is introduced by switching the color, but it shouldn't give a feedback as it does in my unit..
I don't quite understand why the pedal starts behaving like this after years of succesful operation.

Schmatic: http://circuitdiagram.net/wp-content/up ... effect.jpg

Anyone got any pointers?

[Fender3D]

Since SS has no buffer neither on output mixer nor on input (where feedback get mixed) is very sensitive to stuff connected BEFORE and AFTER.
check it out with just guitar and amp..

[GorillaHuman]

Thanks for the reply Fender3D; I have it plugged in with just a guitar and amp. Audioprobing around gives the siren sound on all OTA's when Color is engaged (pin 2,3 and 7 I believe). Could it be an input transistor going off-balance when another stage is introduced in the circuit?

[Fender3D]

you get the howl 'cause too much signal (feedback) re-enters on input.
Try first with some Boss or Ibanez effect before SS (they're low output impedance even in bypass).
Otherwise try rising the attenuation of the cell 27K/3K3/4K7 before the switch. (rising 27K and/or 3K3 and/or lowering 4K7)

[Fender3D]

oh
I forgot...

btw make sure no B52 hovers over your amp

[GorillaHuman]

Ill bring out my anti-aircraft gun this weekend and report back!

[GorillaHuman]

Yup, problem solved. There was a 2k2 instead of a 3k3 resistor. Up'd it to 10k and bye bye rush to raidshelter! Thanks.