Help needed fixing Deluxe Memory Man...

[Mojofuzz33]

Hi,

My first post here so hopefully following the right protocols!

I have a DMM (I guess reissue bought new 2007); board EC2002 Rev E. Closest schematic I have found on line is Rev D though apart from SA571vs NE570 seems a match. This model has 4xMN3008 Chips.

The issue:  The Pedal works normally for short delay times, up to 1/4 to 1/3 of the delay knob (pot). Then the delayed signal drops out. Clean signal remains.

Tests done to date:

- Audio probed signal pre and post delay drop out but nothing obvious.
- Checked power supply and ground to all chips. All seem OK.
- Tested "clock" frequency coming out of CD4047 (pins 10/11) pre and post drop out (basic test with Multimeter); pre drop out clock pulse  seems ok, post drop out clock pulse stops (aha!).
- I have not disconnected delay pot to test properly (yet) but test in circuit shows 0 to 100k values expected and also tested input on RC common (pin 3) which it controls through full rotation of delay pot with no obvious issues.

So seems have isolated issue/symptom to CD4047 chip and the clock pulse dropping after 1/4 turn of delay pot. I am therefore assuming the issue has to be with the CD4047 chips itself or one of the controlling components in the immediate vicinity; a few caps and resistors?

My next step would be to work through testing / replacing these components but before I pull out my long retired soldering iron just wanted to check my logic and see if there were any other options I have missed?

If it helps at all pedal went in to storage for a couple of years and this was like this on return.

Any help / thoughts greatly appreciated.

I have built a few fuzz/od boxes in the past but this is my first play with modulation/delay so my knowledge is limited based on a week on Google and reviewing related datasheets!

This is the schematic I have been referring to. http://www.scribd.com/mobile/doc/125892267

Cheers, 

     M

[cjlectronics]

Don't rule out a bad delay pot.  I've seen where the wiper, internal to the pot, will make contact for half of the sweep and then, due to gunk and dirt build up, not make contact the rest of the sweep.

[Mojofuzz33]

Thanks, will include in my test / swap of components in the timing circuit.