So dropping the frequency din't work. I was able to isolate one hashing board which is causing the trouble. Every day it would cause the PSU to shut down so I have it connected to it's own PSU. This helps by preventing the whole miner dropping out which has bought me some time.

I am hoping someone can shed some light on what signals to the PSU to shut down that the hashing board is triggering. One thing I do notice is when I attempt to probe the 6 pin connectors connected to the hashing board to test the voltage, the PSU shuts down. Visibly I cannot see anything which could cause a short. Bare in mind that it only happens when the ambient temp gets to about 38C.

I will clean the contacts up with some contact cleaner to see if that helps.

Cheers