A2337 new M1 MacBook Air problem Logic Board related, no video backlight 820-02016

[corintosh]

Update:
I checked the capacitors again with respect to ground and one Side is 0 Ohms the other 2.5 Ohms.

How would I proceed when attempting to add power to find the short?, can I take the usb connector from the chassis, connect it to the logic board on the desk and the board will consume power by itself without other components?

I would then try the method using alcohol to see where it gets hot first.

Should I try other things first?

[mon2]

Hi. See attached. The stains are suspects on these capacitors unless proven innocent.

Remove all power / no battery. Meter in resistance mode.

Measure the resistance across these capacitors which are likely in parallel so they share the same end pins. That is, if one measurement is off, then every measurement in this cluster will be the same. Start here and pick any of these 3 caps and post the resistance in ohms. Again, no power to the board (only power to the people).

[corintosh]

Hi thank you very much for trying to help me,

Meter in resistance mode:

2.7 Ohms
0.002 kOhms

[mon2]

Ok. Definitely a short on this region. Be sure the lcd is not connected to the board. This will confirm the fault is not inside the lcd assembly.

Locate the diode that is linked to this backlight circuit. Flux it and lift up one leg with tweezers. Do this only if you feel comfortable. If not, wait.

An adjustable power supply will be helpful now. Using a power supply configured to 1 volt, inject this voltage onto the backlight rail. The very low resistance will force all shorted capacitors or parts to heat up and crack under pressure. IPA (alcohol) will help but not yet necessary. It should be obvious soon after this process as to who is shorted.

[corintosh]

The lcd is not connected, in fact the logic board is entirely out of the case.

As I am just starting out repairing my own devices, I do not own an adjustable power supply. If there is no other option, I might be able to borrow one from a friend.

Diode meaning DP800, as shown in the attached pictures?

I will do it a couple of times on a similar component on my throwaway board of another 2009 MacBook, what temperature would you suggest using hot air?

[mon2]

Yes, this is the diode that is in series with the backlight rail. The removal may not be necessary.

Remove all power. Meter in DIODE mode. Place the red meter probe onto the anode (back end of the arrowhead of the diode in the schematic); black meter lead to the capacitors that are showing this short. The meter should conduct.

Reverse the meter leads, the meter should block. The IC is also mated with this diode which may throw off our tests but wish for you to test. The goal here is to narrow down the search for the shorted part(s). From the visual, fairly confident the issue is with the observed capacitors.

Yes, do lean on your friend for this quick test or consider to purchase one from Amazon. The holidays will delay the arrival. You can always return it if you do not want to keep the unit. Based on the low resistance, 1 volt should be enough on the power supply - dial up to support 3-5A of current. This combination should be ample to heat up the shorted part(s).

If you wish to isolate this diode, suggest to flux the part. The heat and air pressure will vary with the tool but we often use 350-400 degrees with low air pressure in tight circles to melt the flux and then then the solder. Then with tweezers, gently lift up one leg (of the part; not yours). Suggest to watch some YT videos on the topic and test with donor boards.

[corintosh]

I can borrow the power supply tomorrow. It can deliver up to 30v / 5A.

Measures in Diode mode:
Red probe to anode, black to cap: 0,354v
Black probe to anode, red to cap: 0,811v

Thanks again for your guidance.

[mon2]

Yes, power supply will be ample for this exercise. Start with 1 volt at 5A and review who is heating up. Only if necessary, increase the voltage slightly. This rail is not mated with the CPU should it should be safe to consider a higher voltage but for now, keep at 1 volt. The general rule for power injection is to keep the injection voltage to the lowest voltage used by the logic board. This is for safety reasons in case this same rail is shorting to the CPU, then the CPU is not killed from this exercise. For now, do not worry about the diode. Most likely the diode is fine.

[corintosh]

I educated myself a bit more on the topic, if I understand correctly since there is 2.7 ohms resistance we need more than the equivalent in ampere since we should not use more than 1 volt. That is probably why you suggest 5A so it heats up enough?

Should I still take the diode out of the circuit prior to the voltage injection?
As far as I understood I will be soldering jumper wires onto ground and a suitable pad to inject the voltage, can you recommend spots I should use?

[mon2]

Yes, 5A current should be ample at 1 volt setting. This setting will allow for the power supply to inject upto 5A of current onto this short. This is plenty to heat up the low resistance parts which we are suspecting to be one or more of the caps with the strange stains.

We use meter like probes for our injection tool we purchased from Aliexpress - 'Short Killer 30' which claims to inject upto 30A of current. We usually dial the tool upto 0v8-1v0 (max) and inject ground to ground; red probe onto the caps showing the short.

You should be fine to solder a piece of wire (use one with multiple strands) onto the backlight power rail. Black remains to ground. The removal of the diode should not be necessary but can be removed if you wish. Note that there is a polarity to this diode so take a pic of the part before and after removal.

[piernov]

I educated myself a bit more on the topic, if I understand correctly since there is 2.7 ohms resistance we need more than the equivalent in ampere since we should not use more than 1 volt. That is probably why you suggest 5A so it heats up enough?

That's not how Ohm's law works. 1 V over 2.7 ohms would pull 0.37A (assuming the resistance stays constant, which is false but beside the point). Which would coincidentally (not really, that's just because voltage is 1 V) dissipate 0.37 W, and that can be difficult to detect without a thermal camera. So voltage may have to be increased to generate more heat.
Regardless, starting at 1 V is always a good idea.

[corintosh]

Got it, he also has probes for the bench power supply, so I could do it the same way.

I checked the capcitors again under a microscope and found that one of the „stains“ looks more like a crater with some metal colour shining through.
Since I will have the power supply tomorrow would you advise me to inject the voltage or just try to remove the caps?

I will probably only be able to continue the day after tomorrow so thanks again and merry christmas to both of you, I am thrilled to keep this updated.

[mon2]

Based on the shared pics, these 3 caps are the suspects. Not sure what is going on the other side for the same power rail. For now, perform the voltage injection to confirm what you see. The capacitor you are observing will most likely crumble with the injection.

Merry Christmas to you as well. Will continue to monitor this forum while attempting to learn about micro python, a very buggy language.

[corintosh]

Hello all, I hope you had a wonderful christmas.
I got the bench power supply and injected 1v at 5A (which immediatly went down to ~0.337) into the short circuit.

The resistance still reads 2.7 ohms but there was a slight visual change in three of the caps, see the attached photo.

Should I increase the voltage?

[mon2]

Review the caps on the opposite side of this board. Are those caps ok? Suggest to flux and remove these 3 caps. Leave the caps blank on the board. Then test the resistance again.

[corintosh]

Hey, I did remove the five rightmost capacitors and two smaller ones underneath them by accident…
For now I didn‘t attempt to put them back.

The resistance between ground and the removed caps still reads 3.4 ohms so it did not change very much.

I also saw this mark under the microscope that I missed earlier (see attached photo) it is also present in the pictures after the voltage injection (see the picture of my last post) but definitely was not there before.

Since this happened certainly when I injected the voltage, does this suggest the chip is bad?

[corintosh]

Also, is there any way to figure out how much resistance I should measure in a healthy circuit besides having a second known good board?

I thought of removing more components of the backlight circuit but since I do not know what it should look like I wouldn‘t know when to stop.

[corintosh]

Review the caps on the opposite side of this board. Are those caps ok? Suggest to flux and remove these 3 caps. Leave the caps blank on the board. Then test the resistance again.

I marked what I took off (again the other two capacitors were by accident...), I rechecked the other side and they look as clean as the remaining two on the side I worked on.
Resistance is 3.4 ohms. Would you advise me on removing more capacitors from the LCDBLT? Maybe the remaining two or the ones from the other side?

I still am confused by the mark on the backlight driver, should I wet the board with IPA and again inject voltage to see if it dries quicker on the backlight driver?

Thanks for your guidance!

[mon2]

Post a pic of your meter face with the 3.4 ohm measurement. Need to confirm the units. The referenced dot may just be the pin #1 marking on the IC from the silicon vendor. Yes, you can pour some IPA to check if it evaporates quickly on the IC. If the caps are truly @ 3R4 ohms, then it will that area that forces the rapid evaporation of the alcohol.

[corintosh]

Post a pic of your meter face with the 3.4 ohm measurement. Need to confirm the units. The referenced dot may just be the pin #1 marking on the IC from the silicon vendor. Yes, you can pour some IPA to check if it evaporates quickly on the IC. If the caps are truly @ 3R4 ohms, then it will that area that forces the rapid evaporation of the alcohol.

The meter is in manual mode lowest possible setting, so it should be correct. You can review the attached picture. The resistance is equal on the empty pads.

I also attached a photo that suggests the caps are okay, they all read within the 2.1 and 2.25 uf.