Brown Betty trimpot/gain knob stuck between high gain and really high gain

[Kroars]

So, built two more Brown Betty’s one works great one works ok…. All components tested prior to install (except for IC’s).

Problem: On one of the two the trimpot doesn’t affect gain much at all. Almost like it’s always full CW even when turning. I can’t get that low gain level when the Gain knob is turned full CCW like I can with the others I’ve built. The only real difference I’ve found is that on the good pedal the pins on IC’s are standard 9v on pin 8 and close to 4.5 on others. On the bad one they’re all the same except for pin 7 on IC2 which reads 3.4v.

Also on C22 the good one goes from 4.498 to 4.489 and the bad one goes from 4.555 to 4.407 when adjusting trimpot. Seems like a bit of a difference.

IC’s were changed from good one to bad one -same issue. Also replaced trimpot -same issue.

Anyone have an idea what to check next?

Thank you!!

 

[Robert]

Pin 7 of IC1 should have continuity to the Red circles in the pic above, not blue.

Turn your Gain pot to minimum and measure the resistance between pins 6 and 7 of IC1, then turn the Gain pot to maximum and make that same measurement again.

You should go from around 22K (at minimum) to over 1M at maximum (or significantly higher than 22K, depending on the accuracy/impedance of your meter).

 

[Kroars]

Pin 7 of IC1 should have continuity to the Red circles in the pic above, not blue.

Turn your Gain pot to minimum and measure the resistance between pins 6 and 7 of IC1, then turn the Gain pot to maximum and make that same measurement again.

You should go from around 22K (at minimum) to over 1M at maximum (or significantly higher than 22K, depending on the accuracy/impedance of your meter).

Thanks!! Double checked with the red circles and we have continuity to pin 7 on IC1. In reference to measuring resistance of pins 6&7 of IC1 -what if my meter starts at 28M (gain pot minimum) and ends around 28M (maximum)? Got a fluke 115.

Do you know what would cause pins 6&7 to sit around 28M despite gain knob being changed from min to max? I’ve already changed the pot out and tested it prior to installing, so it’s got to be something other than the pot.

 

[music6000]

I had Pin 7 & R9 CIrcles reversed, You should have Continuity between Gain 1 to L1 - K to L2 - A to R9!
This should be correct :

 

[music6000]

I had Pin 7 & R9 CIrcles reversed, You should have Continuity between Gain 1 to L1 - K to L2 - A to R9!
This should be correct :
View attachment 15190

View attachment 15194

Have you got Continuity between all the Blue circles now?

 

[Kroars]

Have you got Continuity between all the Blue circles now?

Yup. Just had a chance to re check. Continuity on all circles you outlined. This is driving me crazy. It’s so strange. Tons of gain and pedal sounds great, it’s just that the Gain pot has absolutely no effect on it. I mistakenly mentioned the trimpot on the title, but I see now that it does affect it a bit (definitely makes the LED’s shine brighter when turned up). Just seems the Gain knob does absolutely nothing.

At this point I’ve replaced the trimpot, the A1M Gain pot as well as L1 & L2. Maybe I should try replacing L3 & L4? I’m at a complete loss on this. Never came across an issue like this where everything works great except for one potentiometer.

 

[music6000]

Are you positive you have Continuity between Leg 2 & 3 Pads on the Gain pot, there is a Trace between them?

 

[Kroars]

Are you positive you have Continuity between Leg 2 & 3 Pads on the Gain pot, there is a Trace between them?

View attachment 15282

Ok, now I don’t have continuity between red circles on gain pot and red circles on L 1 or 2……. I don’t know if I somehow missed that before or if it’s intermittent. Although I definitely do not have continuity there.

Im guessing the fix would be a jumper between the pot and L-1? Thanks again for your patience and help!!

Edit: now I have continuity! Thank you again, pedal works as it should now. You’re awesome!!

 

[music6000]

Ok, now I don’t have continuity between red circles on gain pot and red circles on L 1 or 2……. I don’t know if I somehow missed that before or if it’s intermittent. Although I definitely do not have continuity there.

Im guessing the fix would be a jumper between the pot and L-1? Thanks again for your patience and help!!

Edit: now I have continuity! Thank you again, pedal works as it should now. You’re awesome!!