I moved customer's NEC Aspire IP1NA system to new location.
There was no power in IT room so I plugged in KSU in another room and waited for electrician to get power to IT room.
Now 60% of the time when I plug in or unplug a phone seems phone displays go blank entirely.
I reboot and it comes up after few minutes.
Any thoughts to a fix?

Thank you

First make sure the phone is dead and not simply the display contrast being turned down in a default power down. Use the volume keys when the phone is idle to adjust the display contrast.

Do you know what else is on the circuit you have the KSU connected to?

I went on a service call 2 days ago for a DSX periodically re-booting, customer added a fridge and microwave to the same outlet.

circuit is dedicated.
contrast is not the problem, all phones lose their functions.

Well, other than swapping out the power supply, I would isolate the system off the house cabling (even tail) to see if that isn't the issue of power being fed back into the card causing the circuit breakers to kick in. I have seen this with other systems or where someone had run the things in series and you end up plugging 2 phones on one port.

I installed new cabling for CAT6 jacks and brought old tailed out 66 blocks with me, so the only cross connect is what I put in.

So you've tested the cable and inserts then? Plugging in a phone cord into a cat 6 insert can also cause issues. Try a new power supply? Verify the blocks if they are m1 or m2? Just trying too help you trouble shoot. I aways start at isolating.

I hear you Coral Tech. Seems that just unplugging a phone and then plugging it back in is just too much draw for the NEC power supply?
Possibly? Probably?

Just replace the power supply then and see what happens. I have never seen one boot a system then not power phones but hey.

Those Aspire phones are notorious for dead displays. I have been in offices that 79 out of 80 phones now have bad screens.

I believe you may have a bad station card. I have seen it several times just plugging in a phone shuts just that card down .When you reboot the card it will work fine until some one moves a phone

You may have a bad station card .I have seen it several times just plugging in a phone will shut down the card when you reboot the card it it works fine until someone moves a phone