Powering off/crashing during startup MacBook Pro mid 2009 I have a MacBook Pro mid 2009 that crashes during startup after the chime and once in a blue moon gets as far as the login screen before crashing.

Crashes during safe reboot or recovery reboot too

Hardware test from original cd works but finds nothing wrong
Smc reset changes nothing

I have another 2009 MacBook Pro and on interchanging them the following parts work fine

Hard drive
Logic board
MagSafe port
Heatsink
Fan
Sata cable
Battery
Ram

Any ideas for tests or parts to check that might be able to crash the whole computer during startup would be appreciated!
Try an Apple Hardware Test by holding down the D key: https://support.apple.com/en-us/HT201257