Thank you, meltDown,
Today I found something that I've never seen before in my history of playing with batteries!
I use a 6 pack of 1.5v AA batteries to power things. (9V) (There is a reason!)
When I took out all the old, flat batteries, 6 of them, from the packs, they got mixed up with the brand new ones in the box.
No problem, a multi-meter does wonders!
The first battery I tested showed -0.21v!
OK, check the leads into the multi-meter, all OK, red to pos, all OK.
Next battery showed -0.19v
Next battery showed 1.61v, (a bran new battery) so the meter is working!
I found that 5 of the 6 batteries all showed a negative voltage!!
As the switch had been left on for two weeks, the UNO had slowly drained the batteries to a point that the polarity of them had changed!
I've never heard, nor seen of that.
I don't think that there are many PCB's around that will tolerate reversed polarity, and so my UNO has slowly fried itself.
So just a message to all inventors out there, TURN OFF THE BATTERIES!!!!!
Now I just have to buy another UNO, they aren't all that expensive!
Thank you.
Mick