Issue with power on the SL1100

[Tripoth]

For two days now one of my client's SL1100s is powering down. Coming back up in about 20 to 30 minutes. Powering back down, etc. Only seems to be happening later in the day.
Moved the power of the system to another circuit and it is still going on.
While asking the client(via phone) I found out a few more odd things.
Seems that there are two extensions still working when the system 'powers down'. There a probably a couple more. I think they are on the same digital card since their extensions are close in number. Will verify tomorrow when I go into programming.
Lines are also working on these extensions.
There are 3 digital cards and these extensions are on the last card, I think.
I either have 2 malfunctioning digital cards or one of the power supplies in the cabinet is malfunctioning. These are my thoughts.
Any other suggestions?

 

[belevedere]

Your logic sounds good. I would also look into a potential heat issue in the room since it happens later in the day. Around the same time? Is the system on a dedicated circuit? Is there a piece of equipment on the same circuit drawing more power later in the day? AC system? ETC.