madbeanpedals::forum

I'm having a problem with my new Glam chorus. It was working fine for a few days, but now it sounds the same engaged or bypassed (engaged sounds a hair quieter, but no chorusing effect). When I apply power, the chorus works for about 2 seconds, then it clicks into a normal (dry/unaffected) sound.

I'm not one who understands the hows and whys of a schematic, but I can follow it and I know how to solder (okay, maybe not the cleanest) and use a DMM. Photo attached and voltages listed below.

Here are the substitutions I made from the parts list. Unless noted, I used the part specified on the parts list:

• Resistors are 1/4w, so they're standing upright
• R1 is 4M4 instead of 4M7
• R19 is 2K2 instead of 2K
• D2 & R16 is omitted
• R20 is omitted (my on-off LED is attached to the footswitch, so nothing mounted in LED on the PCB)
• C1, C16 & C18 are physically large, but rated at 10nf as specified. C18 is mounted under the PCB because of its size.
• IC2 is a TL072 instead of TL062

Here are voltages:
IC 1 - PT2399

• 2.1v
• 1.08
• 0
• 0
• 1.07
• 0.68
• 2.01
• 2.01
• 310mV
• 50mV
• 51mV
• 304mV
• 1.06V
• 1.06
• 1.06
• 1.06

IC 2 - TL072

• Varies
• Varies
• Varies
• 0
• Varies
• Varies
• Varies
• 9

Regulator
I - 9
G - 0
O - 2.06

Q1
D - 6
S - 1.54
G - 0

The Regulator and C11 get pretty hot when powered. Perhaps a bad regulator since it's only putting out 2V instead of 5V? Can anyone see something obvious as to why the pedal isn't working? Thanks!

-edited to add photo PCB underside photo-
-edited again because I got the IC pinout wrong  :-[ -

hi,
not much of a help, but your tl072 doesn't get 9v on pin8 while regulator does, that is strange as they are on the same potential - trace.
Did you check for shorts between anything that is close but should not be connected?
you can also try to take out the ICs and measure voltages on socket pins, see if they change, if you get 9V on tl072 pin 8 and PT2399 pin 1 maybe something's wrong with the ICs

Quote from: BaklavaMetal on March 28, 2019, 04:46:16 PM
hi,
not much of a help, but your tl072 doesn't get 9v on pin8 while regulator does, that is strange as they are on the same potential - trace.
Did you check for shorts between anything that is close but should not be connected?
you can also try to take out the ICs and measure voltages on socket pins, see if they change, if you get 9V on tl072 pin 8 and PT2399 pin 1 maybe something's wrong with the ICs

Thanks! the TL072 is actually getting 9v on pin 8... I just did the pinout wrong. oops! I updated the original post.

Doing some more testing, I meter the output of the regulator as I apply power. It gives me 5V for a few seconds (during which the pedal sounds fine), then drops. The effect sounds weirder and weirder until regulator output hits 2.5V, then it goes dry (no chorus effect). This sounds like a bad regulator, yes? I'll have to dig through my stash when I get home to see if I have another one I can put in there.

Thanks for your help!

Seems like you are losing the chorus because the delay chip stops getting the power it needs.    I would try swapping out the regulator, although if you see the same behavior after that try checking/changing c19 and c20.    Something that briefly works may be tied to a capacitor that is breaking down after being powered momentarily.

Quote from: zgrav on March 28, 2019, 06:36:02 PM
Seems like you are losing the chorus because the delay chip stops getting the power it needs.    I would try swapping out the regulator, although if you see the same behavior after that try checking/changing c19 and c20.    Something that briefly works may be tied to a capacitor that is breaking down after being powered momentarily.

Hmmm... good to know about the caps. Thank you! I'll try some things out in the next day or so and report back.

While I was replacing the regulator, I noticed that I had C11 in backwards  8)

New regulator, and C11 with proper polarity, and it's working now!

glad you got it working.