Macbook Pro A1707 820-00281 Stuck @5V

[JasonC89]

So I have an Macbook Pro that came in for no power (I dont do a lot og Macbook repairs). After some testing I found it was only getting 5V with very little current draw, if any.
I searched around for shorts, and didnt find any. No real signs of liquid damage etc.

Following a couple of questions from other members here I was able to further test voltages etc. Im now at a point where PP3V3_G3H is showing, but only at 2.23V.
I have 5v on the Enable pin.
Also the dual diode D6902 is showing :
5.19V @ Pin 1
0v @ Pin 2
4.15V @ Pin 3

L6900 is measuring @ 2.23V.

I thought mayber a problem with the diode D6902, or the regulator, but I removed R6923 to isolate it,and now I get the expected 3.4V out from L6900, and also pin 3 on D6902 is showing 5V also.

Im not sure where to go from here? ISL problem or problem with one of the CD3215?

Thanks

[mon2]

Remove all power. Meter in resistance mode (not diode).

Measure the resistance to ground of PP3V3_G3H.

Post your measurement. With an output low voltage, there may be a heavier than normal load on this power rail.

[JasonC89]

Remove all power. Meter in resistance mode (not diode).

Measure the resistance to ground of PP3V3_G3H.

Post your measurement. With an output low voltage, there may be a heavier than normal load on this power rail.

I get about 60k and it rises slowly as I keep the probes on it.

[mon2]

This resistance is fine - no short here.

5.19V @ Pin 1
0v @ Pin 2
4.15V @ Pin 3

That is a large voltage drop on pin # 3. Remove all power. Meter in resistance mode, not diode mode. Measure the resistance to ground of pin # 3 of D6902.

[JasonC89]

This resistance is fine - no short here.



That is a large voltage drop on pin # 3. Remove all power. Meter in resistance mode, not diode mode. Measure the resistance to ground of pin # 3 of D6902.

Yes I thought that too, removed D6902 and it still had the same power drop? I then removed R6923 and I got 5V on pin 3 of D6902 (D6902 still removed), I then resoldered D6902 back and the voltage stayed at 5V on the pin 3 output.

testing the resitance of pin 3 D6902, I again around 300k, which again rise slowly as I keep the probe on it.

[mon2]

U6903 sounds to be defective. Confirm the FB resistors @ R6910-R6913. U6903 may need to be replaced. Keep R6923 off the board till this rail is stable and matches the schematic voltage. BTW, yours is the 2nd case in the 2nd day with an identical fault @ U6903.

[JasonC89]

me

U6903 sounds to be defective. Confirm the FB resistors @ R6910-R6913. U6903 may need to be replaced. Keep R6923 off the board till this rail is stable and matches the schematic voltage. BTW, yours is the 2nd case in the 2nd day with an identical fault @ U6903.

Okay, so you think U6903 is defective even though after I remove R6923 off the board, pin 3 on D6902 seems to be normal and also pin 2 of L6900 shows the correct 3.4V, instead of the 2.2V I was getting with R6923 on the board?

I thought removing this resistor is isolating the circuit from the rest of the board, and since it seems to be working properly now, the issue must be part of the circuit after R6923 pulling the voltage down?

I may be completely wrong as I think this may be the first macbook board Ive worked on, so Im learning as I go.

I will try remove the FB resisitors and test (they're so tiny Im afraid I will lose one lol).

Oh wow 2nd in a couple of days, I must have missed that post, can you link me?

Thanks for your help so far.

[mon2]

Okay, so you think U6903 is defective even though after I remove R6923 off the board, pin 3 on D6902 seems to be normal and also pin 2 of L6900 shows the correct 3.4V, instead of the 2.2V I was getting with R6923 on the board?

Missed that - my bad. Then this regulator is OK but if 2v2 then something is wrong. If you add R6923, the voltage tanks to 2v2? That is, under normal load, this rail should remain stable @ 3v42. Your FB resistors are fine - do not mess with those.

[mon2]

820-00281 - Badcaps

[JasonC89]

Missed that - my bad. Then this regulator is OK but if 2v2 then something is wrong. If you add R6923, the voltage tanks to 2v2? That is, under normal load, this rail should remain stable @ 3v42. Your FB resistors are fine - do not mess with those.

No worriee, just making sure in my thinking. Yes, if I add R6923 back, voltage drops back to 2.2V? Something must be pulling it down?

Ive checked resistance again with R6923 removed and get over 500k on pin 2 so no sign of anything short that side.

[JasonC89]

Ive done a bit more testing on U6903 just to check voltages coming out.

With R6923 in place :
1. P3V3G3H_VBST = 4.88V
2. PPVIN_G3H_P3V3G3H = 4.14V
3. P3V3G3H_LX = 2.23V
8. P3V3G3H_BIAS = 4.13V
9. P3V3G3H_FB = 0.66V
10. PM_EN_P3V3_G3H_R = 4.91V

With R6923 removed :
1. P3V3G3H_VBST =7.63V
2. PPVIN_G3H_P3V3G3H = 5.01V
3. P3V3G3H_LX = 3.4V
8. P3V3G3H_BIAS = 4.98V
9. P3V3G3H_FB = 1.02V
10. PM_EN_P3V3_G3H_R = 4.99V

Not sure how significant these are but just thought I would test both with and without R6923 so it can be compared.

[mon2]

I would consider to replace this regulator and also D6902. If practical, start with D6902 and test again. It appears that this regulator wimps out upon applying a typical output load.

[JasonC89]

I would consider to replace this regulator and also D6902. If practical, start with D6902 and test again. It appears that this regulator wimps out upon applying a typical output load.

Yeah I may just replace the diode.
I do actually recall it getting hot (using thermal camera) when I first started testing. Found a low resistance on pin 3, that went away when I removed one of the 2 caps on the line.

Jow I just need to find a replacment as I have no macbook boards, but plenty of windows laptop donors.

[mon2]

The diode is a jellybean dual common cathode type. For testing, remove this diode and bridge pins # 1 to # 3 on the PCB. Then test again to see if the voltage is stable with the load.

Consult the datasheet of this diode to note the pinout for this bridging.

[JasonC89]

The diode is a jellybean dual common cathode type. For testing, remove this diode and bridge pins # 1 to # 3 on the PCB. Then test again to see if the voltage is stable with the load.

Consult the datasheet of this diode to note the pinout for this bridging.

Okay I'll try this when I'm back working on it in the morning.

Thank you 🙏

[JasonC89]

The diode is a jellybean dual common cathode type. For testing, remove this diode and bridge pins # 1 to # 3 on the PCB. Then test again to see if the voltage is stable with the load.

Consult the datasheet of this diode to note the pinout for this bridging.

Unfortunately still the same, which I thought it may be as I was thinking about it last night. I removed diode previously and still got the drop on pin #3 until I removed R6923.

I removed the diode again and ran a wire from pin #1 to pin #3, plugged in charger and I'm still only getting 5v. Pin #3 on D6902 is still getting pulled to 4v, resulting in only 2.2v on R6923.

Could it still be the regulator?

Could 3.4v be injected on R6923 to see if we get 20v on the charger, or is that risky?

[JasonC89]

Anything else you suggest mon2 before I send this out?
Thanks

[mon2]

What is the exact voltage of PPBUS_G3H ?

With no power, what is the resistance to ground (not diode mode) of PPBUS_G3H @ F7000 / F7001 (check both sides).

[mon2]

Could 3.4v be injected on R6923 to see if we get 20v on the charger, or is that risky?

Given that there is no short on this low current rail, you could consider using your DC power supply and limit the current of your external power source to 500mA and inject as you are considering @ R6923 (without R6923 installed). This will confirm that U6903 is defective since it wimps out upon attaching the downstream (consumer side) load.

[JasonC89]

What is the exact voltage of PPBUS_G3H ?

With no power, what is the resistance to ground (not diode mode) of PPBUS_G3H @ F7000 / F7001 (check both sides).

It's 2.2V when R6923 is on the board.

I'll double check the resistance when I'm back.

(I did notice that when testing one of the left side type c port, the voltage dropped from 2.2v down to 1.7V. I get 2.2V on R6923 on from the other 3 ports.