MXR 100 Phaser problem

[industrialarts]

Can someone give me a little help here? It's a simple circuit but it's got me confused. I made some negative progress in that the oscillator was working but isn't now. One question, shouldn't I be able to make the opamp oscillator work without the buffer stage (Q4)? Also, the Center Freq and Intensity are for changing the bias of the Darlington pair?

Thanks for any help. This should have been an easy fix but has me vexed. The original complaint was not enough depth to the phase and it appeared that there might not have been enough current drive to the optos. I have swapped out the electrolytics (tantalum), the opamp and Q3 & Q4 and was going to replace Q1&2 when I got back to it today and found the oscillator to be not oscing. All the voltages seem to be OK

 

[Bo Deadly]

Yes, the oscillator should oscillate without Q4. Do you have a scope?

 

[industrialarts]

Yep, got a full bench here. Thanks for your reply, I thought so but just needed a thumbs on that, can't figure where the intermittent problem is - it's starting to look like a bad resistor or resistors, kind of not usual but IDK. Replaced everything else and checked for bad traces - i'll put it back under the magnifying lens when I get back to it.

Thanks