Power issue in a pedal

[Electron Tornado]

I'm fixing a Rocktek chorus pedal for a friend and noticed something strange between using a battery and a wall wart. I verified the external power jack is working correctly, and I get the correct power to the ICs with either battery or external power. What's strange is that the LED lights up noticably brighter with just the battery. When external power is plugged in, the LED dims, but the sound from the pedal doesn't change. The battery measured 8V and the wall wart measured 9v.

I wired up a wall wart power plug with a battery and plugged that in to the external power jack. Still the LED was dimmer.


Any ideas what's going on?

Here's a schematic:

[GGBB]

Perhaps C31 is leaking DC.

[Electron Tornado]

If C31 was leaking DC I think it should do it with just the battery as well, since the battery + side is connected to that cap when nothing is plugged into the external power jack.

The pedal sounded fine in either case, and it's in the mail. I'll ask my friend to let me know if he has any problems with it.

When I first got the pedal in, it would engage with battery and the LED would come on. With external power, however, the pedal would come on, but the LED would only blink dimly and go out. In both cases there was no oscillation, and I found C19 in the LFO section was bad. Replaced that, and the pedal worked fine, except for the LED issue I described in my original post.

[GGBB]

If C31 was leaking DC I think it should do it with just the battery as well, since the battery + side is connected to that cap when nothing is plugged into the external power jack.

That's right of course.    I was trying to see a difference in the powering setups and momentarily thought the battery power was coming in elsewhere.  The only difference I see is that schematically the ground points are connected by the D1-R40 combination, but I don't know what that could do as it should be shunted out when the cable is in the input jack.  Maybe there's some difference between how the power socket is grounded versus how the input jack is grounded that doesn't show up in the schematic.  Is the input jack ground okay?  That might explain it.  You're not using a stereo input cable plug are you?

[Electron Tornado]

I was using a mono plug on the input. I had also tried re-melting the solder on the power jack and cleaning the contact surfaces on the inside of the jack, even though a check with an ohm meter showed no resistance.  The pedal sounded fine, but the LED thing is still a bit of a mystery to me.

[WaveshapeIllusions]

How long does a battery last there? Only thing I can think of is current capacity. Perhaps the audio portion draws enough current to load down the power supply.

[Electron Tornado]

How long does a battery last there? Only thing I can think of is current capacity. Perhaps the audio portion draws enough current to load down the power supply.

Not sure, but remember:

I wired up a wall wart power plug with a battery and plugged that in to the external power jack. Still the LED was dimmer.