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

[mon2]

Using the same 600 ohm meter scale setting, touch the meter probes together. What is the resistance in ohms?

[corintosh]

Using the same 600 ohm meter scale setting, touch the meter probes together. What is the resistance in ohms?

Just checked it and it fluctuates but always comes down to 0.1-0.3 before then randomly going up again.

I also just saw that there is a component missing that is in the schematics: CP830, it is already missing on the first picture and the board did not have previous work done.

[corintosh]

First of all, happy new year!

Using the same 600 ohm meter scale setting, touch the meter probes together. What is the resistance in ohms?

I doubt it is the meter but I cannot find any shorted capacitor, I took off the 14 capcitors from both sides and they all are okay. The resistance still is at ~3.7 ohms.

How would you proceed now?

[mon2]

Thank you! Happy New Year to you as well.

Flux and remove the diode @ DP800. Take a picture of this part for proper orientation when you solder it back onto the board. There is a polarity to diodes.

After the part is removed, test the resistance to ground on each side of the diode pcb pads. We are trying to isolate the parts on the board to locate the source of this short. That is, is the short before the diode or after the diode?

[corintosh]

So I removed the diode and the resistance to ground with respect to the anode (upper pcb pad) is in the hundreds of kOhms and rising. The resistance to ground wrt the cathode is 3.6 ohms, so the same as before when we measured the suspicious capacitors.

I had a look which components could also lead to a short resistance path. It seems like there is a resistor (RP832) and some more very small capacitors that are possible candidates.

Thanks for your patience with me, how would you proceed now?

[mon2]

Ok. Confirm if you have a component @ RP831. If yes, flux and carefully remove this part. It is a tiny 0402 device so proceed with patience. This will isolate the backlight IC from this equation.

[corintosh]

Ok. Confirm if you have a component @ RP831. If yes, flux and carefully remove this part. It is a tiny 0402 device so proceed with patience. This will isolate the backlight IC from this equation.

I was able to remove it on the second try…
Still 3.7 ohms wenn measuring from ground to the pcb pads where the capacitors were.

Update: I checked the schematic again and figured it could be a capacitor next to JP600, using the microscope I saw some „spider web“ pattern on the bigger one and took it off.
The resistance now is 3.4 ohms…

[mon2]

At this stage, the LCD is disconnected, the backlight IC is isolated so it is down to the cluster of remaining caps.

To confirm the IC isolation, measure the resistance to ground of CP830 (this is a no stuff capacitor but we can use the SMD pads for measurement). This test should be of a high resistance. Confirm it.

Then we are back to the voltage injection again to hunt for who is causing this short. Based on that we should be completely isolated, it is ok to increase the voltage on the injection to say 2 volts or more. Double check all work before proceeding but the guilty party is within the cluster of remaining caps in this cluster. The resistance is fairly low and the part will heat up with the proper injection.

[corintosh]

At this stage, the LCD is disconnected, the backlight IC is isolated so it is down to the cluster of remaining caps.

To confirm the IC isolation, measure the resistance to ground of CP830 (this is a no stuff capacitor but we can use the SMD pads for measurement). This test should be of a high resistance. Confirm it.

Then we are back to the voltage injection again to hunt for who is causing this short. Based on that we should be completely isolated, it is ok to increase the voltage on the injection to say 2 volts or more. Double check all work before proceeding but the guilty party is within the cluster of remaining caps in this cluster. The resistance is fairly low and the part will heat up with the proper injection.

Thanks again for your ongoing help and patience, I like to think I am getting somewhat better at this but that would be all to you.

I can confirm the IC is isolated 150 kOhms at CP830 wrt ground. The LCD is disconnected, although the connector is still on the logic board.

I will check the boardview again to see which capacitors are left and try to find the short using voltage injection and alcohol. I will report back what I find (or don‘t find)

[corintosh]

At this stage, the LCD is disconnected, the backlight IC is isolated so it is down to the cluster of remaining caps.

To confirm the IC isolation, measure the resistance to ground of CP830 (this is a no stuff capacitor but we can use the SMD pads for measurement). This test should be of a high resistance. Confirm it.

Then we are back to the voltage injection again to hunt for who is causing this short. Based on that we should be completely isolated, it is ok to increase the voltage on the injection to say 2 volts or more. Double check all work before proceeding but the guilty party is within the cluster of remaining caps in this cluster. The resistance is fairly low and the part will heat up with the proper injection.

I checked every capacitor that is left in the backlight out multiple times injecting up to 3.5V. Nothing changed, no cap dried noticeably faster than the others (that is.. they all did not really dry at all).
When swapping the side I also swapped the probes by accident and therefore injected with the red probe to ground.. could this have caused damage?

The only thing I noticed after injecting voltage is that the resistance now is at 4.2 ohms so a tiny bit higher.
Do you still suspect the remaining 9 capacitors?, if so should I try it with even higher voltage?

[mon2]

When swapping the side I also swapped the probes by accident and therefore injected with the red probe to ground.. could this have caused damage?

Perhaps. Not sure but let us continue to confirm either way.

Suggest to carefully flux and remove the balance of the 9 caps to hunt down the shorted component. Respectively, restore each back onto the board if found to be not shorted.

[corintosh]

Suggest to carefully flux and remove the balance of the 9 caps to hunt down the shorted component. Respectively, restore each back onto the board if found to be not shorted.

I started removing caps and the first one directly seemed to add on to one low resistance path. It is a tiny 0201 resistor (CW196) and removing it immediatly increased resistance to 6.1 ohms.

I do not have a clue how much resistance there should be, so I would not know when to stop. It is probably safe to assume this did not resolve it and I continue removing caps?

As for the reassembly I will probably ask somebody more experienced to solder the 0201 and 0402 caps and can only put the bigger ones back. I also decided to buy replacements for all caps I removed because some looked dodgy and they are a couple cents each. They will arrive in a couple of days.

[mon2]

Still too low for the resistance. Keep plucking.

[inflex]

Just weighing in here, I've had a lot of these units, and yes, keep removing those caps one by one; eventually you'll probably find one with a crack on the underside. They can be sneaky!

[corintosh]

Just weighing in here, I've had a lot of these units, and yes, keep removing those caps one by one; eventually you'll probably find one with a crack on the underside. They can be sneaky!

First of all thank you for your quick visit, flex and your videos. You are the reason I tried looking up what it could be in the first place, I did not know you are around here as well, what a lovely surprise.

Still too low for the resistance. Keep plucking.

I cannot thank you enough for your continuous support. Reading the original thread I thought „lets give it a try with this quality help, it might work“ and I sure learned a lot and had plenty fun.

I removed everything. There still is a low resistance path somewhere. At some point, while removing the last caps the resistance went down to 5.4 ohms again.

Judging by the boardview there is only the tcon connector (the port on the board, I removed the connector cable) left within the circuit.The pins look fine, I don‘t know if there is still a chance to find and fix it.

[mon2]

If the LCD connector has not been reworked then it is not the fault. There are a lot of caps on this backlight rail. Hate to ask but can you post a list of the caps you have removed in this process? Suspecting that someone has been missed and is the guilty party. For example, the caps in the DESENSE area have been removed?

These are in section F = Backlight Desense Capacitors.

[corintosh]

Sure, that is completely fair.

Top side:
CP867 - CP873
CW194, CW195, CW196, CW18D, CW18B, CW18A
CP600 - CP604

Bottom side:
CP860 - CP866
CW18F, CW18E, CW18C, CW197

Also DP800 and RP831 are still off and CP810 and CW1A8 I removed earlier by accident. These are still off as well.

[corintosh]

If the LCD connector has not been reworked then it is not the fault. There are a lot of caps on this backlight rail. Hate to ask but can you post a list of the caps you have removed in this process? Suspecting that someone has been missed and is the guilty party. For example, the caps in the DESENSE area have been removed?

These are in section F = Backlight Desense Capacitors.

Just checked your example, those should be the five caps next to the display connector CP600 - CP604. I compared my board to the boardview in flex and had all components in PPVOUT_LCDBKLT marked. The caps in there are all off. If there are other caps, that need to be removed they are still on.


Edit:
I also checked each pcb pad under my microscope after I removed the last caps and looked for solder bridges but there weren‘t any. If you want I can make some photos of the areas I removed the caps from. Maybe I am missing something.

If it is not a component I forgot to remove, do you have an Idee what else it could be?

[inflex]

First of all thank you for your quick visit, flex and your videos. You are the reason I tried looking up what it could be in the first place, I did not know you are around here as well, what a lovely surprise.

Yes, I spent quite a bit of time here in Badcaps, have been here for many years now ( Just don't post a lot ).

Starting to worry that your board might have an internal short at the rate it's going; based on that cooked off inductor in the original posts it might have happened, hopefully not. Looks like Mon2 is guiding you though. Best of luck.

[mon2]

Yes, do post pics of the logic board with the removed caps. Also a pic of the LCD connector on your logic board.