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This 820-00850 board has 3 of 4 ports at 20V. The remaining port (USBC_TA) cycles between 5V and 0V when plugged in one way, and remains unresponsive when plugged in the other way. I checked all relevant LDO and power lines and found no shorts. What component could cause this plug asymmetry?

After performing a DFU Restore, I'm now seeing a short to ground on PPBUS_HS_CPU. Looks like the CPU shorted out for good - the USB issue was probably a pre-failure symptom. Goodbye board.

Yes, the 0.9V and 3.3V rails are there.

I replaced U2800 and UB000 and the situation is unchanged.

Since all 4 ports are nonfunctional, are both U2800 and UB000 likely defective?

This 820-01700 board arrived with a single misbehaving USB-C port. I found a shorted CD3215, which I replaced with a location-matched chip from a donor board. Now all 4 ports charge the battery and power external USB drives but don’t allow for any data transfer. External drives are recognized...

Ah, yes. This is also why DFU Revive/Restore fails without a functioning SSD, correct?

This 820-01700 board arrived stuck at 5V USB-C. I found a short on the SSD0 NAND chips: it shows 3Ω to ground on L9530 (P1V8_SSD0) and 2Ω on L9580/1 (P2V5_SSD0). When I temporarily remove L9530 and L9580/1, I get 20V on USB-C (0.03A) and PPBUS is 12.6V. But no chime or startup. Before I...

Got it. So when I see a diode mode reading, for example, on PP0V82_SLPDDR that's half of the value of a good board, it implies that the T2 is drawing too much current?

Some diode mode readings are lower than on a good board but I see no shorts to ground. What causes U7800 to pulse?

This non-damaged 820-01700 board is stuck at 5.2V 0.04A on all 4 USB-C ports. I have PP3V3_G3H_RTC_X and all 3.3V and 1.5V LDOs. PPBUS is 12.3V. PP1V8_SLPS2R and PP1V1_SLPS2R are missing but pulse every second without stabilizing. Does this point to an issue with the PMIC U7800? How to best...

Aha. Just learned something I did not know. When FileVault (Disc encryption) is on, the Touch Bar remains completely dark until after the password is entered. Same for Diagnostics and Guest Mode. I verified this using an identical machine set to my account. So your hint was spot-on: get the...

Inspection showed absolutely nothing. No touch function, no illumination.

This 2020 M1 machine came to me for battery replacement. Works fine now except I can't get the Touch Bar to turn on. The Touch Bar works fine with another logic board in the same topcase. I don't have the customer's password, but the Touch Bar should illuminate on the login screen, correct...

Good to know about the A1990… thanks. I did find an old A1708 display and plugged in its camera flex cable to the T-CON board. I was fully functional. Ok, mystery solved. The original display has a bad camera.

I did replace the small video cable. Camera 5V does appear on the T-CON board. L4002/3 have good continuity.

No. That’s how I knew that the ALS wasn’t working. No screen dimming and no automatic keyboard backlight.

Ok, connecting a newer A1990 display did not restore camera functionality.

I don’t have a display this old. I assume A1990 is not compatible?

Customer states that this A1707 machine experiences intermittent keyboard glitches. Inspection showed nothing strange and no liquid damage. However, camera and light sensor are nonfunctional. I verified that the ferrite bead L4004 is good, PP5V_S0_ALSCAM_F is at 5.1V, and the I2C data lines...