iPhone 6S Short on VCC-Main

[LastDeuS]

This iPhone 6S arrived looking nice with original screen never opened,
The customer claims the phone just shut down in his hands.

Opened and checked full short on VCC_Main out of the housing, On DCPS same as always just Q2300 gets hot.

Checked every Cap visually and they look as nice as they can be

Soldered a wire to the line and there is no heat up to 5A which my dcps got up to 2.45V only (chose 3.8V) (I normally don't like going that high) anywhere on the board used Flir and freeze spray also lips 0 heat.

I have only had a case like this in the past and started removing caps randomly until I got the guy but I'm pretty sure I'm missing something here.

Regards

[Jessa_the_Professa]

Are you sure vcc_main is short? What is diode mode reading? It could be that another line is short and that is why you are not seeing heat by injecting into main.

Consider lines around speaker amp, and backlight anode line. See if your multimeter finds a short on one of those lines. I'm suggesting those lines just because we know that in an unopened phone we have a mechanism for these lines to fail.

[LastDeuS]

VCC_Main is 0.001 on diode I'm using fluke 115

Backlight Anode is 0.185 not sure what other lines should I check here Cat1 and Cat2 have normal readings.

PP_SPKR_VBOOST is 0.437
I also poked around in diode mode for every other cap near the speaker amplifier but could not find any strong shorts, not that I know the value of those lines by heart.

So backlight anode is pretty low but should not be fully shorted in order for VCC_Main to be full short? Could C4023 be causing this? don't think so

thanks for the quick reply btw

[Jessa_the_Professa]

VCC_Main is 0.001 on diode I'm using fluke 115

Backlight Anode is 0.185 not sure what other lines should I check here Cat1 and Cat2 have normal readings.

PP_SPKR_VBOOST is 0.437
I also poked around in diode mode for every other cap near the speaker amplifier but could not find any strong shorts, not that I know the value of those lines by heart.

So backlight anode is pretty low but should not be fully shorted in order for VCC_Main to be full short? Could C4023 be causing this? don't think so

thanks for the quick reply btw

okay, so vcc_main is short and you don't see anything getting hot. There are times when a bona fide short does not generate enough to declare itself, but in this case you have 5A at 2.45V. Heat is generated by watts---and here you have V*A = watts = 12W. If you put freeze spray on a christmas tree and then plugged in the lights---you'd see the lights melt the freeze spray. So something isn't right here. One possibility is that the source of the short is wherever you've soldered the wire. That happened to Mark about two weeks ago. Try moving your wire where you are injecting into main and see if you can find some heat. It is also really common IF the problem is a bad cap, for that cap to have some teeny physical damage/discoloration.

In an unopened 6s, that has no other information or physical damage, then I've seen main shorts under audio ic (dramatic burns under the chip there) on the adjacent audio ic cap, on speaker amp caps, within tigris, and due to a handful of single main caps sprinkled around the board. 6s LOVES to get main shorts, and they can be all over the board. You can be a hero and show us a video using FLIR to shut me up about how thermal cam doesn't really help you fix phones....

[tinker_techguy]

Lol ha ha.. The FLIR Hero!

[crea2k]

I'd turn the board over and check that the wifi ic isn't getting hot. That thing can sink a lot of power before it heats up that much, iv seen a few phones with it shorted now. The problem is unless you have a programmer to unbind the wifi from the nand you can't change it anyway. If your using your flir can ignore the regular camera and hold the camera a max of 1 inch from the board. Now cycle the power off and on every second or two. You should see whatever is short flashing.
for zero ohm shorts I tend to use freeze spray but for ones that don't generate any heat flir cams win hands down, you just have to hold it very close to the board as the resolution is poor. At first it just looks like a blur of colour, but once you find your first component doing it youlll know what to look for.
i only get mine out though if I can't find it using freeze spray as it's a lot slower way of doing it, but it's great for finding very low heat shorts as long as you hold it close enough to the board to be useful as any further than an inch or so and the resolution is garbage.

[Sly]

I would love it if you could show us an example of that when ever you have a chance. What are you using for a FLIR?

[crea2k]

A flir one for iOS 2nd gen, iv got some videos on my phone so il see if I can upload them

[LastDeuS]

Alright I did record a couple of videos but just take my word for the other side of the board it behaves the same way

i tried this cap that you see on the video and the cap on the other end of the board as well and made no difference

the heat will only start and spread from the point of ground contact and the soldered cap on the line

desoldered the audio Chip and looked nice down there still Shorted and soldered back
same result for the speaker amp

https://youtu.be/g369ye7V2F4

https://youtu.be/oHr_AHCGCVk

https://youtu.be/BlHlbAHoSgw

[crea2k]

If the heat is spreading from your ground contact you need a bigger ground contact. I made this mistake when I started trying to do voltage injection and used to solder wires on the board. Now I just either user a crocodile clip for ground and old multimeter probe to inject the power or just two mulitimeter probes, as I found like you that the ground wire always got stupidly hot. Presumably because we are trying to force so much current through a tiny wire, or the connection is poor to the board. I just clip onto a screw hole or shield with the clip and probe with the other end. It's probably safer this way too as you can immediately remove the power probe.

[LastDeuS]

If the heat is spreading from your ground contact you need a bigger ground contact. I made this mistake when I started trying to do voltage injection and used to solder wires on the board. Now I just either user a crocodile clip for ground and old multimeter probe to inject the power or just two mulitimeter probes, as I found like you that the ground wire always got stupidly hot. Presumably because we are trying to force so much current through a tiny wire, or the connection is poor to the board. I just clip onto a screw hole or shield with the clip and probe with the other end. It's probably safer this way too as you can immediately remove the power probe.

I do not use a wire for the ground contact but a needle with a slightly round tip I'm not sure if it can be seen on the video but you think I need something bigger? it's actually bigger than my probes which are super fine

Also how much current can you push with your old multi-meter? I saw someone on the group mention they used even more than 10 amps sometimes to find the short but my multi-meter is the same one jessa recommends only goes to 5A

[Jessa_the_Professa]

Current is not pushed—voltage is pushed, current is consumed. I almost never go above 2.5A.
i would solder a thick wire and not use anything fine if you are looking for heat.

[eDigitCom]

I be afraid to put more then an 1A into an iPhone. has II see when it powers up at 0.6 A and may go to 0.9A with a 3.9V Jessa when you say you not go above 2.5A would this be with a voltage of 3.9V. To go to 5A I be thinking the phone would blow UP UP and UP

[Jessa_the_Professa]

I watched your video. You have too much heat. Turn the current limit down so that you give the board a chance to let the heat from the component declare itself.

[crea2k]

Zero ohm / low on shorts are way easier to find with low voltage and freeze spray anyway. As if you go blasting 4 volts into it and your power supply doesn't have a current knob like mine you end up blasting 10 amps into the board which isn't ever a good idea, plus the board heats up that fart you can't see what heated up. Il start at like 1 volt or something and work my way up if it's a higher voltage line. I deal with a lot of water damaged boards so most of my shorts are total phone dead zero ohm ones so easy to find with 1 volt and freeze spray.

[LastDeuS]

I always use only up to 1A to search for the heat and rarely go to 2A if I cannot find anything in this case I used 5A on the video because that was the last attempt to make the culprit burn if possible but not even at 1A and patience could find anything and as usual my customers cannot wait over 3days lol so had to let this one go
thanks anyways for the help Jessa and crea2k

[LastDeuS]

Zero ohm / low on shorts are way easier to find with low voltage and freeze spray anyway. As if you go blasting 4 volts into it and your power supply doesn't have a current knob like mine you end up blasting 10 amps into the board which isn't ever a good idea, plus the board heats up that fart you can't see what heated up. Il start at like 1 volt or something and work my way up if it's a higher voltage line. I deal with a lot of water damaged boards so most of my shorts are total phone dead zero ohm ones so easy to find with 1 volt and freeze spray.

This kind of short makes no difference the Voltage I choose on DCPS even if at 4V when connected to the board the voltage dropped to 0.3V for 1A and if you increase the Amps to 2A then goes 1.1V and so on

[crea2k]

I think it depends on the type of power supply, trying to think which YouTube channel I was watching the other day that explained it better. For example iv got two different ones, one is next to useless for short finding, as if I put a zero ohm short on it, all the red lights come on and it limits the voltage and current, where as my other one is really good, it'll just keep blasting it in until either the board blows up (never a good idea) or the power supply starts to get hot. I only try to hold the probes on for a few seconds though as the big one can chuck in 10 amps if it wants to which is major overkill.