The fault. When connecting the battery after repair the fan runs all the time until I switch on the unit. All boots and works perfectly. As long as I only allow it to go into stanby. If I fully power down, the fan then starts up and I can no longer boot the device without first disconnecting the battery.
The back story. Purchased as a no power on device, Cleaned up minor water damage and had to jumper wire over to the backlight ribbon as it had a burn mark on one trace where it enters the FPC connector. Also fitted a new USB port as very slight damage to one set of connections.
I am guessing that I am missing some water damage somewhere but I have spent a long time under the microscope checking the board. Nothing is showing on the thermal camera as an obvious component fault but I have a suspicion that it may just be the fan controller or select line which is loading something down and preventing the console from booting normally.
I have had a google search and the only references I find are on a redit thread but no solution was ever posted.
I am not yet sure which components are associated with the fan control so if anyone has any further input or even better resolved a similar issue I would apprececiate their input. Karl