A1708 820-00840 No boot - trackpad clicks - 20V 0.55amp

[ahoonid]

Hi everyone.

I have MacBook Pro A1708 with a confusing issue.
The laptop doesn't turn on. Strangely, the trackpad clicks and fan spins. Caps lock doesn't turn on and no chime.

Initially, the amp meter didn't turn on at all on one of the usb c ports. On the other port, I got 20V and half an amp tho (no battery connected).
I replaced the bad CD3215 chip and now it works as well. Both ports turn on with same amp readings.

The initial issue however remains.
No boot. No backlight. No chime. No keyboard. Only signs of life are clickable trackpad and fan spin.
Amp meter shows 20V and goes up to 0.55 amp and after a few seconds stays at 0.49 amp.
With battery I get same results but ofc since the battery is charging, the amo meter goes to 2.1 amp.

Disconnected trackpad with no luck ofc. SMC reset using keyboard works as the amp goes to zero and back to half an amp again.

Board history not known but the bored was in pristine condition. No marks of water damage or corrosion. No prior repairs most probably as well.

Bad CPU maybe? Anyways to confirm?

[mon2]

What is the voltage of PPBUS_G3H? Is it stable?

[ahoonid]

13.12V and stable.

[mon2]

What is the voltage to ground of ALL_SYS_PWRGD?

See attached on inductor check measurements. Believe these are performed in DIODE mode. Red meter probe to ground. Remove all power. Black meter probe to the inductor to test.

Post any suspects.

[ahoonid]

ALL_SYS_PWRGD is 3.24v




I checked all the inductors and wrote my measurments on them.
I see maybe 3 or 4 suspects! But specifically L7900 and L806 seems to be too low. L7030 seems to be a bit too high as well.

[ahoonid]

The closest thing I could find on the internet was https://repair.wiki/w/MacBook_Pro_A1..._at_20V_repair
But I don't have a missing PM_EN_P1V8S0. I get 3.33V on PM_EN_P1V8S0.

[ahoonid]

What is the voltage to ground of ALL_SYS_PWRGD?

See attached on inductor check measurements. Believe these are performed in DIODE mode. Red meter probe to ground. Remove all power. Black meter probe to the inductor to test.

Post any suspects.

Any ideas mon2? Is the CPU fried?

[mon2]

No. To me, the diode readings will be much lower if the CPU is fried. Also, the power good signal ALL_SYS_PWRGD = '1' so this is a good sign which implies all power rails being monitored by this circuit are within specification.

What is the history of this board? Would you have access to a known good bios for testing? There should be some in the bios forum. Be sure to backup the original before erasing and reflashing. If required, can check my database of the same.

[ahoonid]

The seller said the laptop was working just fine before he decided to sell it. He even had photos of the laptop working since he prepared to sell it in good condition. Don't know how much of that I can believe but as I said the board looked real pristine without any marks of prior repairs.

Would you have access to a known good bios for testing?

I have a doner bored. You think I should try the chip from it or reflash the original one with a clean dump?

Cheers.

[ahoonid]

Would you have access to a known good bios for testing? There should be some in the bios forum.

Tried good bios. No change at all.

Another thing I noticed is pressing the power button alone for a few seconds turns the laptop off as when I do this, the amp drops from 2.1V to around 1.4V and the trackpad no longer clicks.

[mon2]

AMPs will be the current draw and the units of measurement will be in 'A' for amps. 'V' will be for voltage measurements.

What is the result if you totally disconnect the trackpad from the logic board and power up?

[ahoonid]

AMPs will be the current draw and the units of measurement will be in 'A' for amps. 'V' will be for voltage measurements.

Of course! : )) I was too tired yesterday and didn't proofread before submitting the reply. Yeah sorry, i meant 2.1A and 1.4A.

Without the trackpad and battery, it's drawing 0.7A. with battery connected and no trackpad, its 2.1A again. In both conditions, the fan is on full blast mode. No chime, no image!

[ahoonid]

What is the result if you totally disconnect the trackpad from the logic board and power up?

Any ideas mon2?

[mon2]

If fans are full blast then the sensors in the trackpad are not being sensed. Review the smbus scl and sda lines of each and every sensor linked to the trackpad.

[FedorUkr]

I have a similar situation and also want to ask for advice. A1708 board 820-00840, no gong no image. The trackpad responds, the fan first turns on for 5-10 seconds, then turns off. If measurements are taken on the board without connecting any cables and SSD, all the necessary voltages appear, with the exception of the graphics power phases PPVCCGT_S0G and PPVIN_S0SW_LCDBKLT. Current consumption during autostar of the board first increases to about 0.5A, then drops and stabilizes at 0.234-0.244A, ALL_SYS_PWRGD - 3.21V, there is short activity on spi flash for about 3.5 - 3.7 seconds. That's all. I tried flashing different BIOSes - no changes. Resistance relative to ground on L7410, L7420, L7430 is 1.9 Ohm. Tell me where to look next or is this a death sentence for the processor?

[mon2]

What is the voltage to ground of PPBUS_G3H? Is it stable?

To me, ALL_SYS_PWRGD - 3.21V, this is a low pull-up voltage and should be ~3v3. Perhaps an issue with the PCH which consumes this voltage rail.

Be sure to use a beefy USB-C power supply. Suggest 100W rated power supply + 100W rated power cable for testing.

Try this bios:

https://we.tl/t-erKf1uZb9U

[dellxps15]

i got some 820-00840 fixed by reflowing the cpu ic u7100 .

[FedorUkr]

Voltage PPBUS_G3H - 13.06 V - stable
I use the proven original charger and power cable
Thanks for the BIOS, I'll try it and write the result, although I don't really hope that it will help.

[FedorUkr]

i got some 820-00840 fixed by reflowing the cpu ic u7100 .

If there are no other ideas, I will change it, I didn't want to do it before, I thought I would find the reason. Just changing everything in a row is probably not the best idea, I have a donor board, but what is working on it and what is not is unknown.

[FedorUkr]

What is the voltage to ground of PPBUS_G3H? Is it stable?

To me, ALL_SYS_PWRGD - 3.21V, this is a low pull-up voltage and should be ~3v3. Perhaps an issue with the PCH which consumes this voltage rail.

Be sure to use a beefy USB-C power supply. Suggest 100W rated power supply + 100W rated power cable for testing.

Try this bios:

https://we.tl/t-erKf1uZb9U

Please tell me what resistance should be on the PPVCCGT_S0G line relative to ground?