Power issues on Model B rev2.0

[abwilde]

I am trying to get my Rasperry Pi Model B rev2.0 up and running. I have a Kingston 8Gb SD card with Raspian Jessie 2017-1-11 image loaded.
I am able to get to the desktop without seeing the 'rainbow box' during startup, I can use it no problem for about 1-3 mins before it will suddenly switch itself off, leaving only the "PWR" light on.
I have tried running the device without a USB keyboard, mouse and Ethernet plugged in yet still, after bootup, the device can sit idle for a few mins then unexpectantly power off. I have even unplugged the HDMI so the device literally has only the power cable plugged in, yet the same problem happens. This is without me even trying to SSH or VNC - it is literally sitting idle before it powers down.
I have tried 3 different power supplies and USB cables but none have made a difference. The power supplies I've tested have given me no problems with my other RPi Model 3's so I don't think they are to blame.
I am at a loss as to what else I can try. I have tried other images in the past, even tried to install an OS via NOOBS and had it fail before installation due to power loss.
Please help!

[DougieLawson]

Get a new power supply or a better cable between your power supply and your Raspberry.

[davidcoton]

How hot is the SoC (main chip on the Pi)?

[abwilde]

Get a new power supply or a better cable between your power supply and your Raspberry.

Thanks, I've tried multiple power supplies and even more cables.

How hot is the SoC (main chip on the Pi)?

According to the Temperature Monitor applet it started at 36 degrees celcius, I opened some windows and web browser tabs, CPU load was at 100% most of the time and temperature slowly raised to 43 degrees before I had another power outage.

[abwilde]

Anyone got any ideas? <45 degrees doesn't seem abnormal does it?

[davidcoton]

Temps up to 80C are fine, so no problem there. If you are seeing a large rainbow box at startup, that is normal. The power low indicator on screen is now a lightening bolt, in any case, so I'm unsure what warning (if any) you are seeing. I'm also out of ideas as to why the Pi shuts down (how do you know it shuts down when the screen is unplugged?)
Does the Pi work with an SDCard from another Pi? Does the SDCard work in another Pi?

[abwilde]

Thanks for your suggestions.

I've tried another couple of SD cards. I suspected that Running Raspian Jesse with PIXEL may have been too much for the RPi v1, so I tried a couple of super lightweight OS's to see if that would make a difference.

Sadly, not. It must be a fault in the Pi... Looks like a good excuse to buy another v3 model!

[hansotten]

Did you try to use another SD card?

[abwilde]

Yes, I've tried a couple of SD cards.