Macbook A1707 short on PPBUS - nothing gets hot

[JM1010]

After using a bad charger (cord chewed by dog...) Macbook died.

Getting 20V and oscillating 0 and .2amp on amp meter

PPBUS is shorted (.8V)
After checking resistance with Vcore (ok), injected 1 amp, then 2 finally 3 amp on PPBUS and nothing seems to get hot except the PCH (barely tolerable to the touch at 3amp.)

If I can't detect anything getting hot @ 3 amp, what else can I do??

Thanks in advance.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

PCH getting hot often means it is game over. However wait on additional feedback from others.

[reformatt]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Use a thermal camera and voltage injection @1V. 3amps should light up like a Xmas tree.

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Thanks Mon and Reformatt for chipping in. I'm dealing with a PARTIAL short @ 50 ohms and this makes it difficult to find anything warm. I wish I had a thermal cam but i don't. I carefully inspected the whole board, applied IPA etc, nothing really gets hot.

As it currently stands PPBUS is partially shorted ( priority) as well as PP5_S5 and PP4V.

The PCH is quite warm but I think it may be normal or due to one of the shorted rails.

I wonder if there are other ways to identify the source of a partial short where nothing really gets hot....

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Locate and remove, for now, fuse F7000 off the logic board.

Remove all power. Meter in resistance mode.

What is the resistance to ground on F7000, pin #1 ? pin #2 ?

Respectively, trying to locate the short and if it is on the source side (U7000 circuit) or sink side (after the fuse).

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Exactly what I had in mind Mon. Really hope it's on the source side.... Irrespective of which side it is, what would be the next step? On the list for tomorrow.

As a side note I also have some PP5 and PP4 rails shorted. Could (should) be related to same problem. Again this is not a water damage board. All happened at once. Weird.

I'll buy some freeze spray, should help till I can put my hand on a thermal cam such as the seek pro.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

We do not own a thermal camera, yet, but have had very good luck using IPA from Costco pharmacy dept. The designs of the camera keep improving daily and the price continues to drop.

We have used 0v8 of voltage injection and this process highlighted the IPA soaked tantalum that was at fault. Personally would not go much higher as we do not yet know where the rail is going. Freeze spray is expensive as compared to IPA.

The ISL9240 is now readily available offshore - did ping Mobile Sentrix to request them to carry the device as well. We have a bunch of them in transit through Aliexpress, if you are in need of it.

With IPA over suspected parts, the heat mists the alcohol quickly so you can home in on the bad part.

In the meantime, you can also try:

Remove all power. Meter in resistance mode (2k should be ok).

Then use the meter to check the resistance to ground of each mosfet linked to U7000:

source to drain
source to gate
gate to drain

Looking for any low resistance values on the mosfet which may be a factor of the low PPBUS_G3H value and low resistance.

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Thanks a million Mon. I owe you one. Maybe a beer in Windsor some day

[reformatt]

Re: Macbook A1707 short on PPBUS - nothing gets hot

3 amps into 50 ohms....you'd have to be injecting 150V for that to be the case, so your fault is on a sub-rail.

You either have a shorted decoupling cap, or a shorted FET/power IC on one of the buck converters. Shorted caps can be found with IPA and voltage injection, but 0201 caps are very easy to miss using that method. A better alternative is to use a Rosin atomizer dispenser pens instead.

For the dual FET buck converters, just measure drain to source (or Vin to Vsw/Vsw to GND) on each sub-rail. For the power IC's (like U7210 etc), measure Vin to SW (or SW to GND) for a short. If you have a high side FET failure on a sub 2V rail, that usually results in destruction of the silicon.

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Reformat, was tired hope it's a typo. Was careful to keep voltage below 2V and current below 3 amp.

Mon regarding the PPBUS short, I didn't have to pull out the fuse(s) as I think I have my answer and I'm pretty sure the short is on the load side (unfortunately).
Both the ISL coil L7030 and the Q7030/40 mosfet gates are not shorted. Only the Q7040 output is shorted. (PPBUS).

I've poked around and this is what I have thus far. Some of these rails have pretty low resistance to ground. Unsure which are fine, need to investigate some more.

PP5vs5 good, pp5V_S0 3 ohms
PP3V3, pp3v3s5, PP3V0 are fine but PP3V3_TBT 1 ohm,
L2950 VR09V 1 ohms .. should be around 500 I think
pp1V2_s3 150 ohms
PP1v_pch 75 ohms (L8000)
pp1v8 OL
PP1V0 OL
u5400, everything low ohms / shorted including pp3v3_S0 (1.5 ohms) except cpuhi_ioout
The GPU mosfet QA640 and 650 have peeled on top, probably normal as these probably run hot. Unsure.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

pp5V_S0 does not look healthy.

Disconnect (if not done already) the LCD; keyboard; trackpad.

Be sure that the keyboard connector area is clean of any possible corrosion. IPA is great with a Q-tip.

The above rail is all over the logic board starts with a load switch. See attached.

What is the resistance to ground of Pin # 1 (U8209) ?

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

U8209 Pin 1 is pp5v_s4 @ 4 ohms. Other 5V: pp5V_S0 @ 3 ohms, PP5vs5 is good

Correction PP3 rails
PP3V3, pp3v3s5, PP3_S0 are fine PP3_S0_LEFT is 4 ohms and PP3V3_TBT 1 ohm. Maybe something funny going on with U8295.

The board is out of the case. I'll check the connectors nevertheless.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

See attached.

Locate L7600 inductor. A bit of a pain but lift one leg of this coil - carefully. Use flux and heat to melt the large SMD pad to isolate the 5V rail.

Do not power on in this condition.

Meter in resistance mode.

What is the resistance to ground on L7600, pin #1 pad ? pin #2 pad ?

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Thanks Mon, just momentarily pulled it out to take a reading. Unfortunately this short is on the PP5_S4 side (3.4 ohm)Sorry I forgot to record the other side but it did not beep.
So that leaves me with a problem on PPBUS, PP5V_S0, PP5S4 but not S5, PP3V3_TBT, PP3V_S0_left but not PP3VS0. Oh My.... for a no liquid laptop it's quite an handful. Any chance they have one or two things in common? Trying to solve this puzzle logically

[spidertnt]

Re: Macbook A1707 short on PPBUS - nothing gets hot

I have had 2 of these boards with no liquid short on c4206 and c4205

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Funny coincidence Spider, Rene from Macbook Repair Ottawa tried to fix my board and removed one of these caps. Caps were fine, shorts are still there. Board is back with me to fix. Cheers.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

A good tool to have here is a LOW ESR meter. They are not that expensive and you can build one yourself from the article on this website using an Arduino.

With the tool, you can quickly test each part to locate ideally the bad one based on the ESR reading.

There is a youtube on this topic. Let me see I can find it and link it. Just a FYI.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

https://www.edaboard.com/threads/eas...boards.396794/

Watch the video...

[JM1010]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Hi Mon, are you suggesting an ESR is needed to move ahead with identifying the shorts on my rails eg PP5VS4? I still wonder what these rails have in common as all the problems happened at the same time.

[mon2]

Re: Macbook A1707 short on PPBUS - nothing gets hot

Can you clarify which side of PP5V_S4 is appearing to be shorted ?

Is it L7600, pin # 2 = U7650 = source of the voltage rail ?

Or L7600, pin # 1 = sink of the voltage rail ?