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[SOLVED]820-3437 CPU gets hot (motherboard is powered) but not turning on, NO green light.

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george-a

george-a

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[SOLVED]820-3437 CPU gets hot (motherboard is powered) but not turning on, NO green light.

Hi guys,


Another adventure. This one was repaired by someone in the past - that' all I know about its history - also it seems it was LD at that time without serious signs of corrosion.

I can measure power to all coils except L3095 (TB), the CPU gets hot (it also does the macbook-air thing - it turns on-off-on as it should) but there is no chime, no image, no green light.

I also noticed U3210 (also TB) has been replaced or re-soldered in the past.

Any clues?

Already tried different I/O-power board.


thanks in advance guys.
 
george-a

george-a

Member
USB mouse NOT lighting up, tried other IO board, don't have spare flat cable.

L7630 measures 700mV instead of 1.05V?...
 
george-a

george-a

Member
Im using the oscilloscope so I can see the pulse-side and the DC-side thus no room for error :) ..just checked again => 0,68 to 0,7V
 
george-a

george-a

Member
this looks funky.

I replaced U7600 as you said - but I think my oscilloscope tricked me somehow - even with new TPS51916 the oscilloscope reads 0.7V but the multimeter 1.05V (other readings show correctly on the oscilloscope like PPBUS and PP3V42, clocks, etc) - the resistance of L7630 to ground was 189ohms. So it was probably not necessary :) _I just learned not to fully trust my oscilloscope Vavg readings.

Since I have no green light I looked for SYS_ONEWIRE and found it on a pad south of the SMC. I measured that and it jumps all over the place! few mV to 1.5V to 3.4V to 700mV... is that a clue that the SMC could use some flux+heat (since this macbook air was previously - dont know when - LD)?

duke I dont wanna waste your time - let me know your final thoughts and we will probably call it a day.

br,
george
 
D

dukefawks

Administrator
Could be crap under the SMC, but you didn't replace the flat cable which is the #1 failure with no green light. The green light should however not affect the power up of these boards. So yeah crap under SMC maybe...
 
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