820-3332 no video/backlight


New member
Hi Team,

This machines starts, chimes but no display on internal or external screen.
Checked and noticed that F9700 was blown, so I replaced it, after what PPBUS_S0_LCDBKLT_FUSED was present but still no backlight display.
disconnected the screen at J9000 and tested again on external screen: OK
Tried another 2013 retina LCD Screen: NOK

reflowed U9100:
now with the LCD connected PPBUS_S0_LCDBKLT_FUSED jumping between 1.8V to 3.0V, if LCD not connected it stays solid 12.50V
PP5VR3V3_SW_LCD at L9000: 5.0V
If I put a torch light on the LCD, I DO have a Display/Image.
Should I suspect u9701?


Staff member
Are these diode mode readings with red probe at ground?

PPBUS_S0_LCDBKLT_FUSED is practically same as PPBUS_G3H.
Did you note PPBUS_G3H fluctuating too???


New member
Yes red probe on ground.
Ppbus_g3h solid 12,5V
That why I think the fuse was blown, maybe U9701 randomly shorting lcdblkt_fused rail to gnd or having dropping the resistance of that rail close to gnd (low r?sistance to gnd)


New member
Hi 2Informaticos,
you were right the fuse was blown again, so I replaced it.
After what PPVOUT_SW_LCDBKLT was mesuring 55V which means that the backlight boost circuit is working.
I've tried a spare lcd: worked fine
So I disassembled the faulty LCD, then I've found that it had a WD + burn and broken and missing PPVOUT_SW_LCDBKLT pin on the LCD connector.
See attached pictures.
Maybe I can try to fix it
Thank you

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