I have the same problem with a DD-2 (same circuit). With a battery (non preferable) it works good, with a PS not. I tested it in normal (non hold) mode.
1-In the first three positions the led comes on intermittently-more often not at all. I have checked the switch -that is working well because in the fourth position "HOLD "the unit works properly with LED on as long as you have the switch pushed.
2-Same conditions in battery and mains supply options.