Author Topic: Longchip dd-3 faults  (Read 2742 times)


Longchip dd-3 faults
« on: April 25, 2012, 02:28:46 AM »
I recently bought a very cheap faulty dd-3 off the bay to have a play around with to try and get working again and to improve my soldering/electronic skills etc.
Anyways, when it arrived it turns out to be a longchip dd-3 dating from 1988.
The only thing working on it was the led which would only come on in the "hold" position but there was no delay at all in any mode (including the hold position).
It was however passing a clean guitar sound.
Stripping it apart i could see that there were slight scorch marks around the d6 diode and it was very loose and i could see some of the pcb "tracts" lifting as i wiggled the d6 diode.
So i bought and fitted a new correct diode from maplins and because of the scorching around it i've used small sections of wire to connect the components just around the d6 using the pcb tracts as a guide.
I've also relaced the c53 c54 c56 c43 c47 caps.
So now when i connect with a power supply - i still have the clean guitar sound when the pedal is off and now the led comes on as it should do in all modes when the pedal is depressed.
You can, however, only hear the delay very slightly - so in "hold" mode, it activated as it should but you can only really hear the bass strings of the guitar repeating and the sound is low (have to turn my amp up higher to hear the signal).
In the other 3 modes i have to turn the effect,feedback and delay knobs fully to hear any delayed signal and again the sound is low.
Has anyone got any thoughs what i should change now?


Re: Longchip dd-3 faults
« Reply #1 on: April 30, 2012, 10:20:26 PM »
Sounds like the sound getting to the delay section is messed up, maybe an open circuit somewhere, or bad opamp in the preamp section.  Trace the audio up to the input to the A-D section.  The DD-2 schematic is floating around, that should be fairly similar to your DD-3, if you can't find the perfect schematic for your DD-3 version (I believe there are 3 different DD-3 versions).