Hi All.
Does anyone know if Macbooks will power on without their display backlight controller ICs? Explicitly I have an a2485(very similar to a2442) that has the UP800 IC broken/missing. On attaching a USB PD charger it stays at 5v ~1A for 20 seconds and then resets and repeats the cycle.
The history is that the machine was water damaged to IC UP800. A Renesas 209100b1 Buck Boost controller. The machine still worked, but without the display backlight coming on. UP800 wasn't generating any switching signals to the four driver mosfets. I removed UP800 and check the PCB and surrounding components. Everything tested okay. I cleaned and reballed the IC and put it back on the board. On connecting a USB charger, the machine started power cycling as initially mentioned. I removed UP800 again, but it still power cycles.
When the USB charger is connected, the 3v8 AON rail is good and stable for the 20 seconds the machine is on. The PP5V_S2_MAIN rail switches on and off at about 1Hz, as do the 1v8 and 1v2 rails. It's like the machine is trying to bring up the power rails but fails and resets. I fear I may have messed up the reball and sent power down the I2C or EN lines to the SOC. Although I was quite careful and checked for shorts after the reball. Also, looking at the pin layout of UP800 it's hard to see how any of the power rails could short to the SOC lines. With UP800 removed, there is a weird(non-binary) pulse coming from the SOC on the BL_PWR_EN line and SPMI_DISP_BKLT_DATA steps up to 1.2v, both synchronised with PP5V_S2_MAIN's 1Hz. Nothing on SPMI_DISP_BKLT_CLK. There are no pull-up resistor on the schematic which is weird assuming it's i2c.
I'm currently looking at buying a new UP800 from AliExpress but they are extortionately expensive, so it would be good to work out if the current problem with the machine is just because of the missing backlight controller, or if I've damaged something else and it should still power on without UP800. Any help would be greatly appreciated whether it's about the backlight controller or similar failure modes on M1 Macbooks.
Thanks.
Does anyone know if Macbooks will power on without their display backlight controller ICs? Explicitly I have an a2485(very similar to a2442) that has the UP800 IC broken/missing. On attaching a USB PD charger it stays at 5v ~1A for 20 seconds and then resets and repeats the cycle.
The history is that the machine was water damaged to IC UP800. A Renesas 209100b1 Buck Boost controller. The machine still worked, but without the display backlight coming on. UP800 wasn't generating any switching signals to the four driver mosfets. I removed UP800 and check the PCB and surrounding components. Everything tested okay. I cleaned and reballed the IC and put it back on the board. On connecting a USB charger, the machine started power cycling as initially mentioned. I removed UP800 again, but it still power cycles.
When the USB charger is connected, the 3v8 AON rail is good and stable for the 20 seconds the machine is on. The PP5V_S2_MAIN rail switches on and off at about 1Hz, as do the 1v8 and 1v2 rails. It's like the machine is trying to bring up the power rails but fails and resets. I fear I may have messed up the reball and sent power down the I2C or EN lines to the SOC. Although I was quite careful and checked for shorts after the reball. Also, looking at the pin layout of UP800 it's hard to see how any of the power rails could short to the SOC lines. With UP800 removed, there is a weird(non-binary) pulse coming from the SOC on the BL_PWR_EN line and SPMI_DISP_BKLT_DATA steps up to 1.2v, both synchronised with PP5V_S2_MAIN's 1Hz. Nothing on SPMI_DISP_BKLT_CLK. There are no pull-up resistor on the schematic which is weird assuming it's i2c.
I'm currently looking at buying a new UP800 from AliExpress but they are extortionately expensive, so it would be good to work out if the current problem with the machine is just because of the missing backlight controller, or if I've damaged something else and it should still power on without UP800. Any help would be greatly appreciated whether it's about the backlight controller or similar failure modes on M1 Macbooks.
Thanks.
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