old digital delays

[Kevin <kevin@minds-eye.org>]

Thought I'd run this question past you folks.

I've got a couple Digitech 2 second delay pedals (PDS 1002 and 20/20
Multi-play) that have been having some problems recently.  When the
delay signal is held, it modulates (sometime extremely, sometimes
lightly).  Any ideas if these pedals are bound to become idiosyncratic
mystery stomp pedals or is there some (easy-ish) way to repair them?

Thanks for any help

Kevin