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iphone 6s Baseband PMU outputs disappearing

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  • iphone 6s Baseband PMU outputs disappearing

    Initially I thought my soldering was causing this, now I'm not so sure. I took a working icloud locked motherboard and measured the power rails with my multimeter. Initially the voltages were there... but as I continued to recheck the voltages the oddest thing happened - the voltage where I was measuring started to fluctuate downwards. Then when I rechecked all the rails - all the voltages were gone. My first thought was that I must have inadvertantly shorted the IC during measurement?(note I also did the same on another icloud locked 6s and had EXACTLY the same result! I then took an iPhone 5s and measured its baseband PMU voltages - no problems - rock solid, measured again - no problems rock solid. And the voltages are still there! Regards the 6s's - the (Baseband) PMU voltages never returned! Right my feeling with the 6s's is one of voodoo - maybe there's a With doctor in New Orleans sticking pins in 'dolls' of my 6s's? But seriously what could have gone wrong?

  • #2
    hello l2l :-) Jessa and all,

    did you remember that the iphone 6s turns off the voltage over time, leaving only the main and wake-type rails (power consumption dropping down while switch to suspend mode to less than 0,1A) ?
    You have to look after that screen should be on when you take the measurements most lines (except ...main, ...always lines and few sensors).
    By the way, why do you measure the BB_PMU outputs ? What kind of fault you trying fix?


    • #3
      Hello tojaert. Thankyou

      The original 6s phone I am investigating is in setup mode stuck on searching and unable to activate. When I connected to 3U tools I noticed the IMEI was not there. I am assuming the Baseband EEPROM is either dead or just not receiving power from Baseband PMU(hopefully the later).

      This iphone 6s, another phone which is icloud locked, I was only trying to validate my skills against BEFORE I tackled the phone with the searching issue but was getting trolled by the power rails 'disappearing' during measurement.
      1. check for IMEI
      2. check Baseband PMU power rails present
      3. desolder/reball/resolder
      4. check power rail voltages still present
      5. check for IMEI


      • #4
        hello l2l, hello all,

        my friend, you are wrong. Unfortunately, when iPhone is reseted, we lose a first and basic diagnostic tool which is operated iOS. Without that we are blind at all.
        When iPhone is on and system is loaded we got a wide field of view our situation. Why a phone has "no service" issue? Is it just "no service" on the screen, no imei when tap *#06#, no imei in settings or no firmware modem, sim autoryzation problems, no acces to the provider etc. That is a kind of tip (like instruction: what is to do).
        Now, you have two paths: to find and use built-in diagnostic of installed components or change part after part and test their status every time.
        In first path - you need lots of time to learn about linux systems and rules prevailing there.
        ( I used my experiences and knowledge from the "digital alpha unix" from the 90's, which turned out to be extremely useful:
        It is unusual among commercial UNIX implementations, as it is built on top of the Mach kernel developed at Carnegie Mellon University by Avie Tevanian.
        Other UNIX and UNIX-like implementations built on top of the Mach kernel are GNU Hurd, NeXTSTEP, MkLinux, macOS ! and Apple iOS ! :-) and suprise : Mach is originally developed by, Avie Tevanian, was formerly head of software at NeXT (that's so fantastic), then Chief Software Technology Officer at Apple Inc. Are the blocks starting to fall into place :-) ? But this is a story for different time ).
        In second path, as Jessa informed some time ago: in "no service" cases we just can change PMU, sometimes do reballing of BB_CPU or correcting some pads etc. I thing we have got some more possibilities. But yes - tx/rx system is really complicated and it's hard to fix with no understanding of technical rules.
        Firstly in my advice - install all passive components. Be carefully - don't overheat a board. Install a motherboard into known housing and screen. Reinstall software. Read with understanding (or post here) record installation log. This is no matter which system you use for it: iTunes, 3u or other. I prefer 3utool. You will find out if the BB_CPU chip works and accepts the software.

        Last edited by tojaert; 10-10-2020, 11:44 AM.


        • #5
          Hello tojaert.
          Thanks for the reply and insights.
          Ok, to be sure I understand you correctly, When the iphone is in setup mode after a reset the IOS system isn't fully loaded and neither 3U Tools, nor we(manually executing system commands) are unable to read certain information, such as firmware modem, provider details, IMEI?
          Work I did before investigating (Baseband) PMU
          (1) Reballed then, when that didn't work, replaced the tranceiver IC
          (2) Reflowed, then when that didn't work, reballed Baseband CPU.
          Then, when that didn't work, connected the phone to my computer and opened up 3U tools to search for clues. I thought the missing IMEI was a clue. *duh*
          (3) I started up the phone and tested Baseband PMU's power rails for output but could not find any - ever. So I reballed Baseband PMU.
          (4) When that failed I decided to take Baseband PMU off an icloud locked board(a known good - at least the network connectivity of the phone was working - ie could connect to the icloud server and confirm it's activation lock?)... but first decided ro remove, reball and restore Baseband PMU on the icloud locked board first and test for Baseband PMU outputs(just to verify my own work), before getting trolled, assuming it must have been something I did when I measured and PMU outputs were no longer there.

          Yes, I suspected network connectivity issues ARE hard to fix on any mobile phone (unless it's a signature problem) thanks to the complexity of the circuit. I suspect that even with good knowledge it could take hours and even then eventually end in a rabbit hole.


          • #6
            Hello tojaert,
            I will try your last advice and see if BB_CPU is actually working/accepting the software and post


            • #7
              hello L2l, Jessa and all.

              very simply - yes and no :-) . In setup mode we can find just info but it is glitch effect not reason of a fault. Deeper search will show modem or not but also it's also a resulting of a fault.
              In system setup mode a phone is fully loaded but service isn't started ( +activating = started and configured main apple services, serial no. and hardware id confirmed - UI must be ON and have status - READY). You can't pay by apple pay service with no configured and accepted. It has standby status. You can't make a call with no confirmed your position and access in proper cellular mesh (there are exceptions) - system "calling" is loaded but not configured - on standby mode etc. Just in few words: system status in IOS isnt online for every component. That is fact. Imei status in information mode is not online but is result of core queries about components readiness.
              Walking down Jessa's school - why the fault occurred or when, at what point. At which stage the phone was reset. These are important questions which should be asked before (not when reball or swap ic's does not working).
              Answering your question - have you imei on information mode? yes/no (that's info). Have you imei in settings/system? yes/no (that's info), have you modem no. settings/system? yes/no (that's status), can you call? yes/no (that's info), have you SEID? yes/no (that's status), have you ICCID? yes/no (that's status) - most is off-line readings but modem firmware is an exception and finally have you *#06#? that's effect of question to a transceiver module. After system reset you can't make a question above - because your UI can't read information from the system. UI can't be set up because can't finish diagnostic of radio-system because "unexpected error". That's all.
              We are waiting for the effect of filling the gaps in circuits and replacing the software.

              Last edited by tojaert; 10-12-2020, 10:25 AM.


              • #8
                Hello tojaert. Thanks for the reply.

                I think I get your point. The first thing I should have done to was try and reinstall the software, from either recovery or DFU mode, and then see if that cleared the problem.

                I'm not sure that I underastand ALL of what you're saying regarding system info and when it is available to be read, honestly SEID and ICCD(Engineering stuff?) are 'iddish' to me, but I can see you're highly knowledgable. From my limited understanding I 'thought' the only information Apple's icloud servers were interested in were in the handset identifying it's IMEI and serial number which they used to determine whether it is locked to an Apple account. If the handset can't pass/the Apple servers can't read the IMEI and/or serial then setup can't proceed and the phone get's stuck. I thought, when the spot for IMEI for this phone was vacant in 3UTools this may have been a symptom of this particular searching/no service issue.

                But, this phone, has been problematic from the word go. Originally I purchased it from an Ebay seller as a 'no power up' phone. They said it would not turn on(not quite true - ).
                1. It had a broken screen
                I replaced the broken screen and then discovered it was suffering from random shutdowns - battery level misreads - I may have replaced the battery to resolve - I cant remember now.(no this handset is not the same iphone 6s I recently posted on this forum with the same issue).
                2. Then later on the phone developed a short, which caused the phone to run extremely hot . The short(which I removed) was caused by two capacitors on two of Baseband PMU's power rails(no magic here I used visual clues to diagnose - one cap was damaged - the other discolored).
                I thought my woes were over so I factory reset and now the present issue posted on this forum.
                But, at this stage, because of these multiple emerging issues, I'm beginning to suspect that this phone may have water damage. I think I might, at this stage, just desolder ALL the shields for a good look see.


                • #9
                  Just checked my old records for working on this device. As it turns out I did attempt to update the software before mucking around with the ICs......
                  29/07/2020 after attempting to setup the phone standalone. I connected it to itunes.
                  The error from itunes was" iphone could not be activated because the activation information could not be obtained from the device".
                  Then, from itunes, I executed restore and update. Restore and updated completed DFU mode.
                  No change. Still stuck on searching then "no service".
                  25/08/2020 Reflowed Baseband CPU. No change so I desoldered, reballed and restored Baseband CPU.
                  26/08/2020 Reassembled into my known good parts for testing frame.
                  Cycling signal bars searching then 'no service'
                  2/09/2020 replaced tranceiver with known good from icloud locked board. 0mA current draw thru USB, no boot.
                  2A current draw before prompt to boot DCPS. Removed discolored cap - tested short off the board BUT short still on the board.
                  (The phone booted after I located and removed the 2nd shorted cap - both of which it seems were on the main power rail, NOT a sub rail).. ah the value of keeping records when you forget exactly what the problem was. these two caps WERE around the perimeter of Baseband PMU but on the MAIN power rail.
                  unable to activate "no service" 3U Tools doesnot read IMEI as tested assembled in parts for testing frame.
                  removed from parts for testing frame.
                  No outputs from Baseband PMU. 3U tools still does not read IMEI.

                  Phone is a bitch. I'm deslodering the shileds to check for water damage!


                  • #10
                    WATER damage! Enjoy the wonderful view of a water damaged phone! Staring me in the face ALL the time as plunged into the eternal rabbit hole!. What a dick am I? Bidding on ebay for a not working for parts only phone ALWAYS ask if they're the original owner and if the phone has ever been exposed to liquid, water. If they don't reply, don't buy! And if they lie..... you're entitled to return it as NOT as described for a refund.
                    Attached Files


                    • #11
                      I do have one final question. This is an unlocked motherboard. If, for arguments sake I successfully transferred CPU(yes probably next to impossible but not impossible), Baseband CPU, NAND? and EEPROM to an otherwise clean(not water damaged) icloud locked motherboard could I make a reliably working phone?


                      • #12
                        hello l2l, Jessa and all.

                        no, firstly you should have done is checking all marks of "no service" to confirm it or not, on loaded original system (not reseted I mean). But... all in the right order.
                        You have wrong understanding of me. Absolutely. Apples servers are not interested your handset on this level. The clue is cpu, which is need to confirm stability of all platform to be working condition at all.
                        Cpu must confirm installed BB_CPU and validate its number with itself and data in eeprom (in few short words). If pass, goes to activating and ahead. After that we can to registration into iCloud services, but it is not essential for normal work like calling. If not, cpu says: stop! activating problem, go to apple store "(...) and replace your handset (pay extra for 11) or go hell" - that is a joke :-) but some in this style.
                        I skip the theft stage, the blocked icloud account and the previous user's data in it. We're not talking about it. If everything is clear, let's move on.

                        If some software, like 3utool shows blank imei, serial no or other abnormalities that is, something is not working properly or has been installed incorrectly by software. For a thousand different reasons.
                        The same you can find on information page, on reseted handset (mostlly), in settings page in a phone etc.

                        And yes, if imei is blank after reset your handset it is mean you have got "no service" problem. The question is what is the reason for the "no service" fault?
                        We have got few answers on it.
                        it would be a great help to check the phone settings and confirm the numbers in the settings or not. But if the phone was reset beforehand, this solution cannot be used. The milk has run out. All checks have to be done by hand - and that costs time and knowledge.

                        Now, you have to stop work before you devastating your board. And it is not a joke.

                        Tell us some about that two caps which were shorted and decolored. Where it was, what was their values, what lines. When you threw them away, is there at that pads a short circuit at this point? That are a important questions and need be a answered.
                        And finally: start this motherboard on DCPS and screen only. Start it by tweezers. No housing, no Touch button and cams. Just motherboard "saute"