Cap value around MAX77621A south to APU

Hi guys, i recently got a Switch to repair that was taking 0.47A at any voltage and has a lot of capacitors shorted, one around BQ, and a lot around MAX77620A. I was looking to find the reason of the short, and i stumbled on one of the latest Northridgefix video, which was exactly having the same issue. I have the same shorted capacitor in the south MAX77621A to the APU, but he doesn’t say in his video the value as he takes it from a donor board. I have capacitor books, and no donor board, anyone can help ?
https : // www . youtube . com /watch?v=PqV6cyVu-xw

Likely not shorted, search the forum for “CPU is shorted’” in the switch category or “Max shorted” and you’ll find like 100 posts of people thinking the same :smiley:

It would be wise not to follow any instruction or direction from Northridgefix for Switch repairs :slight_smile:

Hi Severence, thanks for jumping in. Frankly speaking, I am looking without always taking any judgment but more to learn and see different ways of narrowing down issues, I am far from being an expert, so I can’t say if anyone is good or bad, I am a rookie in this domain. But in this particular case, since I removed this cap, all the shorts I had are gone. I will search for the posts you are referring to, already read some, but in this case I am not sure if this wasn’t the issue indeed because the cap off the board was also shorted.

No judement from me bud, we’re all learning :slight_smile:

Only mentioned in this case as if I recall in his vid, thie chip in question had clear signs of liquid and corrosion below it, in the process of removing the cap below he may have only temporarily resolved the underlying issue, which I beleive was also the IC itself, again if I recall he even saw it getting hot with his thermal cam prior too… at the very least he should have pulled, cleaned and reballed the IC, at best, he should have replaced it… that and he tosses boards around like dog toys :roll_eyes:

I was referring to

Which many mistake the rails as being short to ground as they are low resistance

If I remember right, the cap which you removed is on 1V8PDR, as a result it would not cause a short to ground on any other rail produced by the MAX77620A nor the BQ / SYS rail

Some news from my side, since i replaced the capacitor, i have no more short on the cap left to the BQ, and the 2 above and the tiny down the Max77621 ic south the APU. I replaced the fuel gauge by precaution, as he also got water damage. But still the Switch doesn’t power on and i still have a current drain of 0.47A in 15V. I need to check for the rails as you mentioned, probably this evening i will start digging around with resistance measurement on various spots, will see. One thing also i noticed was that the CPU was heating up, not too much, but still it was warming up when plugging the charger in, so some shorts somewhere there must be.

I’m pretty sure that cap which you removed from below the max IC is on your 1V8PDR, and I’m pretty sure the cap your reffering to to the left of the BQ IC is on your SYS rail, so your suspected shorted cap below the max IC would not cause your SYS rail to become short to ground as a result, it’s not possibe

Which much like Northridgefix, it’s highly likely the actual fault was on the Max77621 (possibly corrosion below it, I don’t know… your board looks spotless), which is connected to both your 1V8PDR and your SYS rail, and heat when removing the cap has likely (and possibly only temporarily) resolved this issue.

It’s pretty normal for the SoC to warm up up in these instances and doesn’t really indicate a fault

Understood your point, makes perfect sense, and as I use flux it also removes a bit of corrosion I guess. Would you suggest me to replace the Max in this case? I already done Max77620, since I didn’t succeeded in recalling (was trying without stencil like theCod3r shown in a video, got 3 balls merged 2 times and didn’t had the courage to redo it again)with no luck so far. However I replaced the original BQ and fuel gauge, they were looking like mint. Will find the relevant info about the sys rail in the forum and start to troubleshoot with the ad-hoc test points
Will let you know.

It really depends on the severity of the liquid/corrosion, in the case of the Northridgefix video, notice how the liquid/corrsion was black in colour, this is typically as a result of soft drink spills, with cola being the worst offender as the liquid drys out it leaves behind the sugar which turns to carbon and acts as a really great resistor :wink: In some cases blasting it with flux will effectively dilute this carbon mix and will relieve shorts but ultimately, whats going to happen is it’s once again going to dry out… In his case, the bare minimum would have been to pull the IC, clean it and the board pads, and reball, but given this is a CPU regulator I would lean more on replacing it… it is really not worth the risk.

I guess you cleaned the board, but do you have any pics of it in it’s original state so I can possibly see where the liquid corrosion was?

As for reballing the ICs, pick up a bunch of iphone stencils and some decent solder paste, much easier than doing it by hand

I only have that one where we see the battery connector, the area around the Max77621 IC was in a slightly bette shape. Nothing on the rest of the board .
Yes, I think I will need to invest, when I see the time it took me and I didn’t succeeded anyway. Do you have something to recommend for the solder paste? Is the one from Mechanic any good, or better check for a non-chinese brand? Problem with everything outside Chinese brand is that is will be leaded free, I live in Europe.

If you can order from Mouser I would get a tub of the Chip Quik 63/37 paste as that’s pretty good quality. I’ve been testing the BST 63/37 brand (tub version) and it’s alright, consistency is decent but the resulting balls are never shiny… dunno if that’s because the alloy isn’t 100% correct or it’s an issue with the flux they use in it but overall it’s acceptable I suppose… I would avoid the Mechanic brand, I have used there solder wire before and it’s either not leaded or the alloy is some other blend as it does not melt at leaded temps as well as it being incredbly dull (at least in contrast to Chip quik solder wire)

Thanks for your advise, would this and that work in your opinion ?
https : // www . aliexpress . com/item/1005001848426567.html
https: // www . mouser . be/ProductDetail/Chip-Quik/TS391AX10?qs=1mbolxNpo8c8ecy0j0g43w%3D%3D

The syringes will dry out and become unusable whereas at least with a tub you can mix in fresh flux when it dries out

Stencil s alright but is missing lots, get an assortment of iphone stencils to cover the rest

Got it, ordered, thanks, i didn’t know that Mouser is free shipping above 50€ and they seem to not remove leaded product even if you order from Europe. This is nice to know, in the past i remember that the shipping cost was a show stopper.
I also took the stencil i showed you, one for iPhone and one for Samsung , i think it will make it https : // www . aliexpress . com/item/1005001890740971.html?spm=a2g0o.cart.0.0.1d7a3c00O1hTAK&mp=1.
https : // www . aliexpress . com/item/1005003661364185.html?spm=a2g0o.cart.0.0.1d7a3c00O1hTAK&mp=1
Next thing i need to find, a good BGA holder, i have this one https : // www . aliexpress . com/item/33034033566.html?spm=a2g0o.9042311.0.0.dcd44c4dNOZ3UD
but i am not very satisfied, it isn’t really working great, or i can’t use it.

Seems a bit pricey to me

It’s not really made for the smaller ICs, they’re meant for SoC, CPU, GPU etc

This style is best

But as I say, only for big stuff like an SoC with preformed balls. The smaller stuff use the direct heat stencils and paste - no jig needed

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Awesome, thanks, i ordered the magnetic reball holder. I wanted to replace the Max77621, but what a dumb, i only have Max77620, i never ordered the other one, i will have to wait for a new one and give you some feedback. I notice there is a thread “Tools” or so, i will dig into it, just to see if there isn’t any tools i would have miss and someone report good feedback.

Cancel that if you can… waste of money, I beleive @Insomniac had one of these and they’re a gimmick for the most part… magnets don’t like heat

So you only use direct heating stencil without any BGA holder then ? how do you maintain your ic and stencil in place during procedure ? Hopefully i didn’t validated the order yet, because i wanted to buy some Max77621 at the same time :slight_smile:

Right, just hold the stencil down with tweezers

Once you start getting to Ram size and bigger you’d use the jig I mentioned earlier with dedicated stencil and preformed balls

Right, stencil holding, why haven’t i thought about that one :smiley: haha, ok, great, hope to get my stuff soon so that i can report back some good news.

It wasn’t me with the magnetic one, I have been doing it without a jig. Just manually placing a few balls on at a time.