Ibanez AD-80 vintage problem

Stevenrb718 · Post by **Stevenrb718** » 28 Apr 2021, 17:39

Trying to diagnose my AD-80. Running off 2 9Vs, the pedal works mostly properly, except the LED dims when the delay time knob is lowered, and brightens when turning back up. The pot seems to affect the effect correctly, even though in the low delay time range the sound starts to self-delay and feedback like an alien sound, but I figure that can be adjusted with trimpot tweaking. After 30 seconds or so the LED starts to dim til it completely goes out, regardless of pot position, and the effect also ends up just going to a dry sound. I'm assuming this is a power problem of some form, maybe a component not staying charged or something. After maybe an hour and retrying, the pedal powers up again and does the exact same thing til the effect dies off again.

theehman · Post by **theehman** » 28 Apr 2021, 17:59

Maybe leaky electrolytics in the power section? Or a power resistor that's heating up and increasing in value.

Stevenrb718 · Post by **Stevenrb718** » 28 Apr 2021, 22:02

theehman wrote: ↑28 Apr 2021, 17:59 Maybe leaky electrolytics in the power section? Or a power resistor that's heating up and increasing in value.

I pulled a few of the early-circuit capacitors, and all of them checked out great. I checked a few times if I could feel any components getting too warm or shorted out, and I couldn't find anything. I did pull the schematic and checked out the input voltages, and where I'm supposed to be getting 12V I was actually getting around 4V. After waiting awhile to let the whole circuit "cool down," I plugged in again and tried to get as quickly to that same test point as I could and it was reading about 6.5V and falling. I'm assuming something is pulling the voltage down. The only problem I can see is that after the voltage regulator IC, there are a ton of interconnected pieces, so narrowing down where the draw is might be tedious. So I guess I'll start by replacing the 78L12 and just hope that is the issue.

Stevenrb718 · Post by **Stevenrb718** » 03 May 2021, 21:17

Yeah, that didn't work. It lasted much longer than normal after replacement, but still ended up fading out to a clean signal with no LED.

Stevenrb718 · Post by **Stevenrb718** » 06 May 2021, 22:36

Anybody have any ideas? I think I managed to desolder all the component legs one at a time across the entire 12V supply line, and none of the disconnections kept the voltage from falling. When I pulled the voltage regulator IC's output leg and measured it isolated before the 12V supply line, I got a solid 12V without falling. This is why I thought a component on the line was causing it.

graeme · Post by **graeme** » 26 Jun 2021, 05:50

FWIW I had one of these pedals that was playing up. Fixed it by replacing the LED. No idea why but it worked....

Stevenrb718 · Post by **Stevenrb718** » 27 Jun 2021, 13:52

graeme wrote: ↑26 Jun 2021, 05:50 FWIW I had one of these pedals that was playing up. Fixed it by replacing the LED. No idea why but it worked....

Was it acting up in a similar way to mine?