How would you approach this weird modulation problem in my Delay?

[glimmertwin]

...I scored a cheap Digitech PDS 20/20 Multiplay from a friend with the only comment that it doesn't work properly and sounds kind of demented.  I thought for the price it was worth a shot to see if it's an easy fix(plus it's in pretty good condition with original PS).  Now that I have had time to toy with it a bit, I'm kind of puzzled where to start with it.  It has three modes on it - delay, chorus, flange.  The problem is it wants to modulate everything that gets played.  It's as if someone is tweaking the delay time while I'm playing it so that the pitch on the repeats is constantly shifting at random.  It will even work properly for a second or two before it goes into more modulation madness that appears to be random.  This pedal also has a "repeat hold" switch and that does seem to function properly - it repeats the unexpected modulations exactly as they sounded in real time.  This happens on the delay & chorus settings.  In the flange mode, it will seem like it isn't working and then all of a sudden it kicks in after you tweak the pots a bit.  The flange mode actually sounds pretty good and all the knobs appear to function properly except that the effect seems to turn off if any of the knobs are turned too low.  Also, the repeat hold mode in Flange mode doesn't do anything except give a high pitched(but quiet) whine that appears to be flanging in a slow rhythmic pattern. 

I'm really baffled by what this could be - a malfunctioning chip of some kind?  I opened up the pedal and reseated the two main connectors from the PCB to the switches/jacks and tweaked the trim pots a bit to see if they were just set "wacky" but nothing seemed to have worked.  There doesn't appear to be any mods to the pedal and no loose connections when I inspected it.  I tried to reseat all the chips just to make sure one hadn't worked itself a little loose.  I tried running it with the original PS and a battery as well.  At this point, I guess I need to start testing individual components but I don't know where to start and it seems like there a zillion places to check inside this box and I can't fathom what would cause a problem as specific as this.  Any ideas where I should be looking?

I found one page of a schematic in the delay sub-section of the schematics area of this site:
http://experimentalistsanonymous.com/diy/

My unit looks the same as the one on this webpage:
http://www.pointlessblank.com/articles/pds.html

Anyone have any suggestions to get me started looking in the right place?  Anyone have an old pedal repair business as a backup plan I coudl take advantage of?

[glimmertwin]

To make it a little easier, here is the link to the schematic:
http://experimentalistsanonymous.com/diy/index.php?act=download&subdir=Schematics%2FDelay%20Echo%20and%20Samplers&sortby=name&file=Schematics/Delay%20Echo%20and%20Samplers/Digitech%20PDS2020.jpg

[any]

I was just about to start a new thread on my PDS20/20 and I might still, but to awnser some of the questions you have....

The Multiplay 20/20's function all work, meaning that in all modes you are allowed to use any of the controls.
That means that using the "loop" footswitch in flanger mode will give you a loop of a few milliseconds,
resulting in a whine. This is factory behaviour and not to be worried about.
The delay should behave as normal with "speed" and "width" at zero, if it does not, there is something wrong in the part of
the circuit providing the clock signal.

The clock on a Multiplay however is NOT recorded with the audio signal! (which is why I LOVE my 20/20!)
You can adjust still the clockspeed in loop modus and thus speed up or slow down your loop to create noise drones.
Which brings me to believe your 20/20 either has dirty/worn-out speed and width pots messing with the clock signal,
or maybe one or more of the TL062's in the clock generation (top part of the schem) are shot.

I'm about to rehouse mine and I'll start a topic about possible mods since It's by far my most beloved effect I didn't built myself!
(Which means, if you ever want to get rid of it... I'm always looking for a spare!  )

You got a great deal!, Cheers