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820-3437-B - No display after removing shorted C5002 on PP3V42_G3H, which restored Magsafe light and fan.

J

joshAU

Member
Hi all.
Macbook Air A1466 with a 820-3437-B Logic board.

Bought in as not powering on, no lights, display, chimes or fans.
No evidence of liquid ingress - very dusty though.

Found shorted C5002 on PP3V42_G3H rail.

Removed and that restored Magsafe light and fan- still no chime and no display on internal or external monitor.
SMC reset changes magsafe light.
PRAM reset turns unit on, but doesn't seem to do anything else.

Is C5002 vital to functionality?

I've checked out the voltages of various rails, while the unit was powered on, with battery and display connected. .


PPBUS_G3H 8.3V
PPBUS_S5_HS_COMPUTING_ISNS 8.3V
PPBUS_S5_HS_OTHER_ISNS 8.3V

PPDCIN_G3H_ISOL 20.0V
PPDCIN_G3H 20V

PP2V42_G3H 3.42V
PPVRTC_G3H 3.3V
PP5V_S4RS3 5.2V
PP5V_S0 5.2V

PP3V3_S5 3.3V
PP3V3_S4 3.3V
PP3V3_SUS 3.3V
PP3V3_S3 3.3V
PP3V3_S0 3.3V
PP3V3_S4SW_SNS 3.3V
PP3V3_S0SW_SSD 3.3V
PP3V3_S4_TBTAPWR 3.3V

PP1V8_S3 1.87V
PP1V2_S3 1.2V
PP1V05_SUS 1.1V
PP1V5_S0 1.5V
PP0V6_S0_DDRVTT 0.6V
PP1V05_S0 1.1V
PP1V05_S0SW_PCH_HSIO 1V

PPHV_S0SW_LCDBKLT 0V (Should be 50v?) (Diode mode to ground reads 0.557)
PP15V_TBT 0V (Should be 15-17.8v?) (Diode mode to ground reads 0.518)
PP3V3_TBTLC 3.3V
PP1V05_TBTLC 1.1V
PP1V05_TBTCIO 1.1V
PPVIN_S4SW_TBTBST_FET 0V ( Should be 8.6v) (Diode mode to ground reads 0.451)
PPVCC_S0_CPU 1.8V

Any suggestions as to where to go from here?
Thanks.
 
2informaticos

2informaticos

Administrator
Staff member
My first suggestion, do not waste time checking voltage for same power rail in different points.
Next suggestion, do not check Thunderbolt area without connecting corresponding device.
Same as for backlight; searching backlight/image on a board which does not even boot???

Missing C5002 is not the reason of your problem; replace it anyway.
If it was corroded, reball SMC.

Check SPI Bus Series Termination resistors and traces.
Also clean J6100.
Try known good BIOS.

PLT_RESET_L goes high?
 
J

joshAU

Member
Hi again 2informaticos.

Thanks for your suggestions... I'm still learning, as you can probably tell. :)
All good points you make.
I posted all those different voltages in case you wanted them, to save time... but yes... that was a waste of time, lol.

I'll find another C5002 equivalent from a dead board and replace it.
No signs of corrosion anywhere.

All the SPI Bus Series Termination resistors measure correct resistance.

However, SPI_CLK and SPI_MOSI both show zero volts.
The two other SPI lines, SPI_MISO and SPI_CS both show 3.3 volts.

Another thing I noticed is R6102 should be 100K Ohms resistance, but shows as only 65.5-74 KOhms.
However, I did test another, admittedly unknown faulty board, and the R6102 on that one was 74K

I cleaned J6100, despite it looking pristine.

PLT_RESET_L goes to 3.35 volts

I'll have a look for the same board to get a BIOS chip off, but thought I'd post this data in the meantime.
 
Last edited:
J

joshAU

Member
Sorry for the delay.
I had to put this on the backburner for a bit.

OK, I replaced the BIOS chip from another 820-3437-B, and no change. :(
I did notice the CPU is getting very hot.
Still no display internal or external.
SMC reset cycles Magsafe light, power button starts and stops system....
 
J

joshAU

Member
Ah. OK.
I think thats probably the most likely.
I'll move on.
Thanks for your help and advice, 2informaticos, I do appreciate it.
 
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