Korg SDD-3000 Digital Delay - Wet/Dry balance quirky problem

[willshk]

Hello,

New to the forum here.  Would like to seek your kind help in troubleshooting a quirky problem with my Korg SDD-3000 Digital Delay (vintage rackmount).

Symptom:
- When dialing into a new program, the unit works fine
- When attempting in real-time to adjust the Direct/Effect (ie. wet/dry) balance by turning the "Effect" knob, the dry signal immediately cuts out regardless of which way I turn the knob.  Only the wet delayed signal comes through.  Setting at 100% dry yields no sound.
- Even though I can't hear the dry signal,  by setting the "Effect" knob to any desired setting (ie. balance 50/50) and saving the preset, the saved preset -when retrieving it again by cycling the program button back to the preset- reflects the correct new post adjusted mix, so I do have a means of obtaining adjustment functionality after saving.

My guess is by turning the "Effect" knob, I am shorting out the dry signal in some way.  Perhaps some failure on board "KLM-806", which is where the "Effect" control connects to.  Below is a link to the service manual as well as owner's manual. 

Service Manual: http://www.florian-anwander.de/korg_sdd3000/Korg_SDD-3000_ServiceManual.pdf
Owner's Manual: https://www.proun.net/blog/sdd3000_owners_manual.pdf

Any help would be greatly appreciated!

-Willshk

 

[willshk]

Just following up on my initial post.  I notice the potentiometer which controls the wet/dry balance connects to a 4051 multiplixer.  I am suspecting either one of the inputs  on the multiplixer is bad, requiring a chip replacement... or the potentiometer is bad.  Note the potentiometer is a quad-gang 20k linear.

Some questions:

1) Is it possible for only one of the inputs of a 4015 multiplexer chip to go bad?  Note the same chip handles other potentiometer inputs such as intensity and frequency (modulation).  They work fine so I'm leaning towards a good chip and bad pot.
2) Would a bad potentiometer simply "short" out the dry signal as per the symptoms I'm experiencing? 
3) If I had to replace the potentiometer, how would I go along in sourcing a replacement?  Would any quad/4-gang linear 20k pot be fine, or will I need to delve into more specs?  Noted the size dimensions will need to correspond with the PCB layout where the potentiometer is soldered onto.

Greatly appreciate any insight.