A1990 2018-2019 15" Touchbar MacBook Pro

Inject 1V (increase if no reaction), watch for hot spots with thermal cam. Usually it's a bad tantalum cap

Measure PPBUS_G3H to vCORE coils (coils around CPU/GPU) IF those measure UNDER 1Ohm (0.3-0.8) then you most likely have a direct 12V short to CPU/GPU. On this board this situation is always a no fix.

• PP3V3_G3H missing due to a short circuit on the input to PP3V3_G3H creation circuit
• Corroded LDO cap for PP3V3_G3H around a CD3215. On right side of board, check under shielding by SSD under the right CD3215 for hidden corroded cap.
• PP3V3_G3H missing due to CHGR_EN_MVR missing due to bad ISL9240
• PPBUS_G3H shorted to ground.
• Bad CD3215
• Bad CD3215 ROM chip (U2890)
• Corrupted T2 firmware.

If the issue is a bad CD3215, one way to get an idea, is to see which does not boot loop. When you plug the charger in with the USB-C amp-meter, it will turn on for 2-3 seconds, then turn off and turn on again. Whichever port doesn't boot loop usually has an associated CD3215 that is bad. Also, the bad CD3215 will occasionally get hotter than the rest.

T2 firmware can also cause the machine to be stuck at 5v. It is however, important to rule out other possible causes for the issue before re-flashing T2 firmware. Typically machines that have corrupted T2 firmware will be stuck at 5v 0.060 amps and typically will have PPBUS present and PP3v3_S5 missing. PP5V_S5 will often be present. T2 firmware can be re-flashed via Apple Configurator 2, however this will erase data in most cases. Try a "soft" Re-flash first by clicking Advanced options > Revive Device in Apple Configurator 2. Example video: https://www.youtube.com/watch?v=ywvDgn7JR_c

Check PP20V_USBC for each port's resistance to ground.

Check PPDCIN_G3H for short to ground.

USB-C charge port is shorted to ground, inside the charge port. Replace the charge port, it is modular. See if it changes.

First, try a known good battery.

If it doesn't work, check the battery cable going to the board. Sometimes there is corrosion here, sometimes the customer tore the bar on the connector off the connector.

In some rare cases the SMC still is a factor in battery recognition on this board.

Make sure the issue is no backlight, and not no image!

• Blown backlight fuse rarely if ever happens. This board has a current sensing circuit in place that keeps the backlight fuse from blowing if there is a short to ground on the backlight line.
• Short to ground on backlight output due to bad capacitor on output.
• Bad screen - if backlight voltage is 49-55v, could be bad screen, but not 100% of the time. Could be data communication issues.
• Corrosion on current sense vias/traces for backlight to U8400 LP8548

Check the LCD cable and the connector on both the screen side and the logic board side. The backlight power line is right next to the eDP data line for the image. Any minor corrosion here results in 30 volts or more going to the displayport mux, U9850. U9850 is what the dedicated GPU and the CPU's integrated GPU go to before it goes to the screen.

This is a good thing, unlike the 13" machine where the backlight voltage destroys the CPU, here it destroys a cheap chip. Replace U9850, and the screen cable, and the connector(on the screen side and the logic board side) and it will usually be fine.

PP2V5_NAND_SSD0 can be shorted (in this case, PPBUS_G3H luckily didn't go to SSD)

I replaced SSD buck converter but the short was still there, found a shorted cap on the other side of the board C9088 which relieved the short on PP2V5_NAND_SSD0

Do not replace U7800. Instead, put device into DFU mode and select advanced -> repair.The problem seems to be T2 not talking to the PMU correctly. Note, you need a battery connected for PMU to work. Best to completely assemble the device.

The 2019 16" model has the same issue.

Question mark folder

No external boot possible & Recovery does not work

- Check U9080, U9580, U9000 & U9500 and SSD power rails PP2V5_NAND_SSD0, PP2V5_NAND_SSD1, PP0V9_SSD0, PP0V9_SSD1, PP1V8_SSD0, PP1V8_SSD1

- Flash T2, Update Intel Mac T2 BridgeOS Firmware, Boot Mac into DFU Mode Then Reinstall MacOs Via Recovery CMD R

The MacBook seems braindead because the trackpad is reacting for 20-30 sec and then it stops and On again. On the USBC multimeter we see boot looping from 0.06 to 0.14, at 0.06 the trackpad is not vibrating and on 0.14 is vibrating.

Randomly the MacBook starts but for no obvious reason and works fine, once shut down it will not restart On thermal camera the U3000 is getting warm (38-40 degrees Celsius). Once U3000 replaced its starting fine and works properly.