820-00840-A (2017 13" MBP) PPBUS_G3H at 1.1V, USB at 20V but 0.04A flowing, No Power or Charge

vinaypundith

New member
I have a 2017 13" MacBook Pro motherboard (model 820-00840-A) that won't turn on. I measured the PPBUS_G3H line with a USB-C charger connected, and get around 1.08V (instead of 12V?). No short to ground in this line - resistance measures 1K ohms rapidly increasing to infinity.

Fuses F3000 and F3100 are both intact - I resistance tested them. However when I test for PP20V_USBC_XA_VBUS (or the one for the other port) at either F3000 or F3100's terminals, I get zero volts at all. Measuring between ground and either of F3100 or F3000's terminals, I get a 22.8 ohm continuity. Is this a short to ground? How would I find this short? I see there are some adjacent capacitors, one of those?

I probed for PP20V_USBC_XA_VBUS at other adjacent points (including L3300 and L3400 solder pads - my board apparently never had these components) - no voltage at all.
Other nearby voltage rails I probed: USBC_XA_CC2 (and CC1 and CC1/2_CONN) fluctuating between 0.8 and 1.5V, SAVE_CC1A no voltage at all.

Anyone know what's wrong? Thanks in advance!
 

2informaticos

Administrator
Staff member
Any history available, liquid sign?

How do you get 20V on USB-C meter with 0V at F3000/1?
What is R7020 voltage?

Use diode mode to check power rails to ground.
Switch to ohm scale ONLY for very low readings; less than 0.010 usually.

"Measuring between ground and either of F3100 or F3000's terminals, I get a 22.8 ohm continuity"
STOP to check ohm scale (or diode mode) with power applied on the board.
 

vinaypundith

New member
(I typed this a few days ago and apparently never hit Post!)

R7020 appears to be an SMD component who's terminals I can't access. Measuring the lines connecting to it, though, all 4 of them are at 19.98V.

With the USB-C cable connected to what would have been the rear port in the laptop, I get a reading of 382 between ground and F3000 in diode mode. Reading of infinity at F3010, and if I plug the USBC charge cable into the other port, my meter doesn't light up at all (loose connection? Or is this something to worry about?)

No reliable history on the device, but there are no signs of liquid damage (indicators are also still white). I was told this laptop worked a few months ago and sat since, and doesn't work anymore.

PPBUS_G3H test point to ground (screw hole) gives infinity reading in diode mode.
 

2informaticos

Administrator
Staff member
"STOP to check ohm scale (or diode mode) with power applied on the board.
....................................
With the USB-C cable connected to what would have been the rear port in the laptop, I get a reading of 382 between ground and F3000 in diode mode."
Why continue doing that???

"R7020 appears to be .... at 19.98V"
That's good; you should get the same connecting charger on both ports.

"PPBUS_G3H test point to ground (screw hole) gives infinity reading in diode mode."
Read how to properly use diode mode scale (more usefull tips there).

Post U7000 basic voltages; AUX_DET, VDDA/P, EN_VR1, SMC_RST*, AUX_OK, A/BMON.
Use surrounding components as test points; like C7016, C7075/77, R7071/72, etc...
 

vinaypundith

New member
> Why continue doing that???
Sorry, I must have misunderstood, I thought that was one of the things you wanted me to test, when you said stop to check ohm scale or diode mode with power applied to board. By "power applied to board", did you mean the method of injecting 1V?

Measuring between PPBUS_G3H test point and ground with diode mode as instructed in your other post, I'm getting a reading of 480. You were right, I was using it with reverse polarity. Thanks!

U7000 voltages:
TBA_AUX_DET (measured at test point and C7016 pad - my board does not have the C7016 component) : 4.26V
TBA_VDDA: (measured at test point and C7075): 5.12V
TBA_VDDP: (measured at C7077): 5.12V
Very strange thing I noticed, when I had the multimeter probe touched to a screw point and C7077 measuring that voltage, I could hear an audible ticking sound from the circuit board - even though there are no moving parts on it??)
CHGR_AMON (U7000 pin 19, measured at test point next to C7026 and at R5439: 0.01V
CHGR_BMON (U7000 pin 14, measured at test point next to C7026 and at R5438: 0.00V
SMC_AUX_OK (U7000 pin 28, measured at test point next to C7724 and at R7071: 3.39V
SMC_RESET_R_L (U7000 pin 39, measured at R7072 and test point next to it): 3.39V

I'm not sure what you mean by EN_VR1. My schematic for the 820-00840-A does not have this net at all, not at U7000 or anywhere else. I measured U7000 pin 34, TBA_HPWR_EN_L, at R7073: 3.10V. Is this what you meant?

When I measure R7020's connections with the USB-C power cable connected to the other port, I get a reading of 1V or less continuously drifting down. My USB-C power meter also does not light up when connected to this port (the LCD on the meter flashes on for a fraction of a second every few seconds. I tried wiggling and moving the plug - no luck.

Also worth mentioning, maybe? : when I plug into the rear-side port, the one that was working semi-right, my USB-C power meter reads 0.13A coming down and stabilizing around 0.08A, instead of the 0.04 that it was reading earlier. I have made no changes to the board since my last post when it was reading 0.04A, no clue what changed.

Thank you for your time!
 

2informaticos

Administrator
Staff member
Ball F2/U7000 isn't EN_VR1?

Both USB-C ports must have the same behavior.
If not, you have a problem on USB-C area; need to find the culprit.
Please don't make "cardinal refferences" (lef/right, front/rear, up/down); post position component on the schematic/boardview.
Also use schematic instead of boardview, when you mention component pins (especially for BGA chips).

NEVER check board in diode mode, or ohm scale with charger, or battery connected!!!

Reffering to U3100/200, let us know the actual behavior of each port.
Compare diode mode readings on the 4 LDOS of both CD3215 chips.
 

vinaypundith

New member
Found EN_VR1, as you said it's on the schematic. My boardview has it labeled as "PM_EN_P3V3_G3H". Voltage: 3.39V
The two USB-C port certainly do NOT have the same behavior. One does not even light up my power meter, and board voltages are very low (compared with what I've been posting here from the other port)

The working port is the one right next to the CD3215's, and the non-working one is right next to component L2950.

Port A (to U3100) is not functional at all (power meter only blinks on every few seconds, 0.3 or no volts at all test points that you mentioned.
Port B (to U3200) is partially functional, giving the voltages I have mentioned so far on all the test points you mentioned. 0.07-0.08A current flow as measured by USB-C power meter.
Machine does not power on on either port.

LDO readings are as follows:
U3200 (with cable connected to corresponding port):
LDO_3V3 (pin G1, PP3V3_UPC_XB_LDO): 3.32V
LDO_1V8A (pin K1, PP1V8_UPC_XB_LDOA): 1.79V
LDO_1V8D (pin A2, PP1V8_UPC_XB_LDOD): 1.78V
LDO_BMS (pin E1, PP1V1_UPC_XB_LDO_BMC): 1.11V
(All voltages are zero with USB-C connected to other - U3100 - port. Expected?)

U3100 (with cable connected to corresponding port: ALL 4 LDO voltages are zero volts.

Can an issue with U3100's circuit cause U3200's circuit also to not work?
 

2informaticos

Administrator
Staff member
SMC needs to talk with both U3100/200 chips.

"Compare diode mode readings on the 4 LDOs of both CD3215 chips."
???

Check diode mode to ground on CC1/2 pins of U3100.
Also inspect the terminals of the non-working USB-C port (possibly corrosion).
And test both ports in both connection ways; 4 combinations in total.
 
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