A1706 - 5v due short 3.3v LDO

[iMuhtaseb]

Board was OK but after keyboard replacement; we found short on 3.3 LDO on UB300 (CD3215).. I removed it and of course I tore off some pads because its undefiled.. pads are repaired successfully.. diode and continuity tests done Pads were USB_UPC_TA_F_P and TP_UPC_TA_SWD_DATA and UPC_TA_SPI_MISO..

After replacing UB300 the watts consumption lowered since short is gone but still is stuck @ 5v (0.06amps)

I noticed few balls around UB400 so I assumed it needed reball; reballed and replaced it; still 5v.. on both sides

While on the other wing U3200 and U3100 are doing the switch.. turning on and off on ammeter indicating they're trying to switch

UB300 and UB400 are not switching or attempting to

UB300 LDOs are all four present

UB400 LDOs present except for BMC

[mon2]

UB400 LDOs present except for BMC

LDO for the BMC on the active port must be present.

[iMuhtaseb]

I replaced UB400 again.. still on 5v and no BMC

[mon2]

Remove all power. Meter in resistance mode. What is the resistance to ground on this missing BMC LDO rail? Then switch to diode mode. Red meter probe to ground, yes ground. Black meter probe onto the same missing BMC LDO rail.

What is the measurement in diode mode? Both tests will assist us to determine if there is a fault on this missing LDO rail. Again, this rail is only active if this PD controller and USB-C port is being used to power the board.

[iMuhtaseb]

UB400 BMC LDO:

Resistance: 200 kOhms and rising

Diode: 0.536

[mon2]

So no shorts here. Can you inspect the USB C connector pads to see if they are ok? If available to you, consider to swap out the paddle board that houses these USB C connectors. The pads do wear out. We have seen a few with cat urine, etc. onboard and that also will affect the operation of the adapter voltage negotiations.

This article is applicable to study for your case:

https://logi.wiki/index.php/CD3215_Bootup_Sequence

[iMuhtaseb]

Found one problem with UB300 with line UPC_TA_R_OSC it was reading 2.4 in diode mode.. I replaced that UB300

Found another problem with UB400 with lines UPC_TB_DBG3 and UPC_TB_DBG4 they were reading OL.. replaced that UB400 and issue was resolved, 20v back.

[mon2]

Bravo! Well done. What is the current draw? Do you have booting now?

[iMuhtaseb]

well, yes.. it was booting just fine.. and I gave it back to the customer after testing and stressing the computer.. few weeks we come to today and it does not show an image..
It switches to 20v, consumes a fair amount of amperage (goes up to 700 mA then drops to 400 mA) and CPU gets hot.. but no image on screen and I measured CPU voltage its there but GPU voltage is not..

I got it to work one time but it got stuck to the Apple logo not showing anything else...

Another than my previous work on the CD3215s (which are OK since it switches to 20v and powers on) the board is spotless.. what could've happened?!
edit: its the AUX short situation.. I checked the diode readings for both lines they're OK..

[mon2]

Test if you see an image using an external screen. A1706 is linked to flexgate so you may now be fighting a different demon.

https://www.youtube.com/watch?v=5nBiN8Uujlw

[iMuhtaseb]

Yeah I've tested the flexgate scenario; cable is good, I've tested it another screen just to be sure.. no image And on external screen (even bare board) no image, this device usually shows an image even bare board..

[mon2]

Issue may be with the display mux @ U3610. Inspect for damage.

Lid sensor status (trackpad) working ok? Test with the lid open / closed.

This is SMC_LID.

[iMuhtaseb]

I have taken a look at U3610, yes, nothing seems off.. I'm thinking of reflowing tbh.

SMC_LID is a great hint! But sadly it is present at 3.4v Hall sensors are on 3.4v

[iMuhtaseb]

I checked the coils around U4200; ok
I checked the LVDS connector in diode; readings OK compared to OBD and another board
Seen a vid on YouTube where a guy replaces the audio codec jack and it fixes the issue; I didn't find any abnormalities, shorts or high/low diode readings..

[iMuhtaseb]

I found a small crack on U4200; replaced it same thing
I replaced both hall sensors in hopes; sadly didn't fix
I cannot find any enable signal for the screen..

I don't know what's wrong with this haunted computer; could it be firmware?

[iMuhtaseb]

I've put another known-good board of mine to the customers housing; my board showed an image for brief moment and it stopped.. now it is exhibiting the same issue.. I lost a good board 😢

What I connected to board are Touch Bar Display, Touch Bar Touch, Trackpad, Keyboard, Audio Jack, Touch ID, Type-C connectors and display...

Diode mode are ok in LVDS, TB disp, TB touch, trackpad, keyboard, audio jack, Touch ID.. I am yet to test type-c connectors..

[mon2]

There is a lot going on in this thread. What are the symptoms at this stage?

Is the USB C port @ 20v or stuck @ 5v? Current draw from the adapter?

Voltage of PPBUS_G3H to ground? Is it a stable voltage or power cycling?

If the PPBUS_G3H is not within proper range, remove all power -> meter in resistance mode -> check the resistance to ground on PPBUS_G3H.

Also measure the voltage to ground of the SMBUS SCL / SDA lines on the battery connector since they are shared across the ISL and other regions on the board.

[iMuhtaseb]

Sorry about the post, it's been cluttered for my numerous and attempts and recording each step here..

USB-C ports switch to 20v and current draw goes to up 0.8 mA then drops to 0.4 mA and stays there..

Symptoms: CPU heats up.. S0 is present but no enable signals coming to power on the LCD..

PPBUS is stable @ 13v Diode mode 0.454
Resistance mode 55 kOhms

PM_SLP_S4 and PM_SLP_S3 are present

SMBUS SCL SDA lines from 0 to 5 tested with diode mode measurement and compared to another board; they're all similar to my good board.

[mon2]

"check CPU core voltage after 10-15 seconds"
L7210/20...

[iMuhtaseb]

hmmm..

L7210 turns on after PD switches to 20v @ 1v for exactly 10 seconds then drops to 0.92v for a second then drops to 0.65v and stays there..

L7220 same thing; 1v -> 0.92v -> 0.65v
That's a remarkable observation mon2!
Bu what does it mean? 😁