macbook air 820-3437-b fan spin fast and no display

larossmann

Administrator
Staff member
Bad SMC or corrosion under SMC. I bet a good ultrasonicing at 80c for a minute will fix this.
 

TCRScircuit

Super Moderator
Staff member
To me this sounds like some kind of a sensor issue. Almost sounds like PROCHOT is being asserted. There are several resistors around the SMC that have thermal sensor signals going through them. You need to check them. PROCHOT is asserted by Q5159, U7200 and the SMC. Have a look at those components and see how they look.. You need to look at all the resistors around the SMC and measure them. It will be time consuming but the issue may very well lie in one of them. Since the CPU would have vcore if PROCHOT you would still get a light but it would not get hot as it would be throttling vcore heavily. Screenshot (153).png
 

dukefawks

Administrator
Throwing parts and suggestions and we have not even confirmed if CPU Vcore is present. L7310 voltage?
Also no history provided?
 
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