Thoughts on malfunctioning Ibanez AD-80?

[Stevenrb718]

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 pulled many different items on the 12V power rail after the (new) voltage regulator, and the voltage still crashed.  When pulling the output and common legs from the voltage regulator, the input obviously sits nicely around 15V.  The weird thing is that when I reconnect only the common leg and leave the output leg disconnected, the voltage starts to slowly crash again.  I'm confused...

[Kevin Mitchell]

The weird thing is that when I reconnect only the common leg and leave the output leg disconnected, the voltage starts to slowly crash again.  I'm confused...

Here's the schematic

Edit: Sorry I read your post wrong. It sounds like you're using a bad regulator that's shorting the input to ground. Very strange

Give us some photos. Not only do I like to geek out on vintage circuits, but folks here might be able to spot something you're missing.

[DIY Bass]

Not sure about the power issue, but I used to have a vintage ad-9 and self oscillation at low delay times was kind of a feature, not a malfunction.  I am pretty sure there are some songs out there that even make use of it.

[Nasse]

If I remember the led had Ibanez low battery warning system, changes colour when battery starts die. Is there some repeat feedback trimmer inside, someone might have adjusted it

[Stevenrb718]

Well I dropped in the 3rd voltage regulator.  When just the input is connected, I have 16V at the input.  When I add the common leg, I get about 14.5V at input and a strong 12.9V (or maybe 11.9V.  I don't recall, either way...) at the output leg.  When I then add the output leg, the output voltage just slowly drops like a stone.  This is exactly what happened with the 2nd voltage regulator also, until it started to get all wonky.  I'm guessing something must be shorting to ground which may have damaged the previous 2 voltage regulators.  I thought I removed everything shown on the schematics from the 12V rail, but apparently I missed something somewhere.

[Kevin Mitchell]

If I were you I'd do a continuity test on all capaitors inbetween the power rails. If one got burnt up from a bad regulator it could possible be shorted out. I'd say the ICs too but you said you've pulled them to no avail.

[DIY Bass]

With no power check continuity between the power rails after the regulator.  I would be checking ground to power, ground to vref and vref to power.  That will at least give you an idea about where to look for a short.  You can remove the filter caps and the circuit will still run, so that can be a test to see if the short is in one of the caps.  Also do a good visual inspection of the shorting rails.  I had an old pedal once that had pots that were not PCB mounted.  One of them had turned a bit until one lug contacted the casing.  That lug had vref or 9v on it (can't remember which), and so the power supply was shorted that way.