it sounds like you know your way around a system pretty well. It’s odd that you would be having those issues even though followed proper procedures (Assuming everything was done correctly). I know this might sound odd. Try to reapply thermal paste. [br]
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As much you probably don’t want to go through that again. I’ve repair many PS4’s but never had any do that
Thermal Compound i use is Arctic MX-4 (2019 Edition)[br]
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If you figure it out im really interested on what the reason is