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

[speedyaction]

I have 820-3437-b with fan spinning fast and no picture on screen. any idea?

 

[G.Beard]

I have 820-3437-b with fan spinning fast and no picture on screen. any idea?

You getting a chime? light on USB mouse? PRAM reset working?

 

[speedyaction]

pram reset, no chime, cpu don't get hot, usb mouse lighting up

 

[G.Beard]

Any corrrsion, history?

 

[larossmann]

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

 

[speedyaction]

i put another smc and still this same problem

 

[TCRScircuit]

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.

 

[TCRScircuit]

Specifically, Check these guys

 

[dukefawks]

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

 

[speedyaction]

i got it from one of shop am fixing macbooks for so not really know of history: vcore - 0.057v

 

[speedyaction]

L7310 - 0.057v

 

[gcain]

Is it possible for the mouse to light up with a missing VCore?

 

[dukefawks]

USB is MUXed to SMC so could be that is initializing the mouse.

ALL_SYS present? SMC_DELAYED present?