Yes, I can understand the thread is getting longer and easy to loose the issue I am having.
Importantly
After a period of time my Arduino stops providing the pwm wiggling on pin 2.
Even though I still call a function to do so every 100mSec, though it should continue regardless of this call.
All other functions in my program continue to operate normally when this problem is present.
In this test we provide a static value of 512 but on my board, this value will range over 0 to 1023 depending on my PID loop controller, hence the 100mSec update.
The period before the failure occurs can vary, I have found it to be typically one to three days, apparently no set period.
For example I reset my board last night and awoke this morning to find no pwm happening when there should have been, my battery bank hit 30Vdc.
Many thanks Nick for your assistance.
Paul