As these systems are aging they seem to develop the similar problem.... chattering on the boards then eventually the KSU just dies. Looks like a voltage regulator issue on the main board in the KSU. Anyone ever troubleshoot this down to the particular component that most often fails?

I see it mostly on the DX120's Its amazing they all seem to be going bad at the same time.

I would check all the Capacitors 1st.

Found two swollen caps. Replaced them and it allowed the system to boot but really flakey. LEDs blinking look weak and off tempo. Will go further into the ICs to see what I can find.

If you haven't already check power supply output,, could be power supply is getting weak.

when this happens we put in a loaner for 2 weeks and they need to update to a new system. I have noticed as you have, they can drop dead a couple a week sometimes after 6-8 years. its the base layer cabinet, sometimes we just swap out the CPU and vmail with a working used base chassie and good to go.

Yep. Been doing that too. Now I have a collection of bad main boards I'd like to fix if I can ever get the time to sit down and figure out which component is going south.