Boss delay DD-3 (square ship taiwan) problem

[Camarada78]

I have a Boss DD-3 (square chip taiwan version) in my bench with a very weird problem. I found no similar problem online, nor a solution for it. It is driving me nuts.

It passes sound on bypass no problem but as i turn it on it has a constant a noise (that can be clearly shaped by Delay Time, Volume and Mode, but very subtle by Feedback).

- sounds ok on bypass
- noise is there even without input connected.
- all electrolitic caps were changed (!)
- all tantalum caps were checked, ok.
- most ceramics were cheked. too many to keep track.
- many resistors checked.

First i thought it would be a feedback problem (because it sounds as if it has almost infinite feedback). but even removing the feedback pot and the caps around it, the noise continues. I am afraid it is the main chip that's gone bad.

Anyone experienced something similar with this classic pedal?

(Schematic annexed)

[Unluckyfett]

I have the exact same problem, I started another thread about it. Did you ever find a resolution? At this point I'm looking at IC8 as being the problem.

[Unluckyfett]

The problem is the DRAM. I replaced the IC and its fixed now. Hopefully this helps someone in the future.

[redwire]

Thanks for the follow up. Schematic says IC6 is M5M4464L-12 DRAM, I think you meant that not IC8 some op-amp.
Other thread: Boss DD-3 (b) Problem

[Unluckyfett]

Yes and no. IC6 was the problem. When I posted originally, I speculated IC8 because of the waveforms. However, I misunderstood the DAC process, and with some help from another forum, I narrowed it down to DRAM.

[redwire]

OK that makes sense.
Commonly I see guitar pedal's input get zapped from static electricity, the tip of the 1/4" jack which can kill/damage the input stage.
JFET or op-amp if a pedal uses that.