Sorry to resume an old thread, hoping to help.. I had the same startup problem on my TDS420 PSU; after a bit the psu would turn on correctly and continue to work until next day.
Next day the psu wasn't starting again; protection was kicking in every 1-2 seconds.
The main problem was caused from the overcurrent protection; even without load, the protection would kick in.
I've disabled the protection (risky, i know) and now it works correctly.
Let me know if you need more details.
