Sunn Sentura II - treble/bass/contour not working

[thespeakerport]

Hello...

I am working on a Sentura II regarding an issue with the Treble/Bass and Contour controls. It appears that they have no effect on the sound at all....well...the treble does a little bit, but hardly noticeable. I have the schematic and checked all the components around the pots, including the pots themselves and it checks out. The tubes have all been tested and seem to be functioning properly. Volume works great, so does reverb and tremolo. Any idea on what could cause this behavior?

[thespeakerport]

A couple of things to mention....i did swap out the 12AX7, AU7 and 6AN8 to ensure it was not a tube problem and it did not solve the issue. I also had to pull some caps out of circuit to get a good test on them as they were giving me wonky results when wired in.

[loudthud]

Check the ground on the Contour control.

[thespeakerport]

Sorry for the delay in responding....the ground off the contour pot seems solid. The pot measures 26K across the outside pins, the wiper works good, and i am measuring 0.2ohm from the pot to chassis.

[g1]

Turn treble, bass, & contour all the way down, what resistance do you measure from treble wiper to ground?

[thespeakerport]

To answer your question, with all three pots turned down to the minimum setting, i get about 29 KOhm to chassis ground give or take. So I dug deeper into this one and I pulled the 0.022uf caps again. They still tested 'ok'....but out of curiosity, i put in new Panasonic polypropylene film caps I had. To my surprise, treble, bass and contour and back. I am not sure if the caps were actually bad or if the process of replacing them wiggled something back into place. I double-checked all the point to point connections and re-heated/flowed any that looked suspect. Also pulled each pot and give it a good bath in DeOxit....just for good measure while i had it apart. checked it all again and it is still working ok. strange behavior.....but it seems to be working. Going to let it run for a while and see what happens before I raise any victory flags.