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    iMac mid 2010 - black screen on startup -

    Good evening everyone,
    the device in question is a iMac 21,5 pollici "Core i3" 3.06 (mid 2010) - A1311

    I replaced the video card because it no longer did its job, with a new one. Unfortunately it gives me black screen, the backlight is present, if I connect an external monitor everything works regularly. Then I also replaced the backlight inverter board but there were no changes. I then tested the LED strip of the screen and it is O.K.
    What I noticed at the completion of the start-up procedure is a screen turning on that lasts a second and then if I put the iMac in STOP from the power switch and immediately after I press it again the display, after a few attempts it turns on and stays on without problems.
    But if I turn it off the problem shows up again on the next reboot.
    The LVDS cable is O.K.
    I have read and tried various reset procedures without success.

    I ask the forum for help and advice to understand what it could be or what I need to check further.
    Thank you
    Paolo

    #2
    Re: iMac mid 2010 - black screen on startup -

    Please clarify if it's backlight problem or an image problem, you say "backlight is present" but you replaced backlight driver board anyway?
    What is the replacement graphics card?
    Were the symptoms the same before replacing graphics card?
    No damage to LCD connector or components around/behind it?
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

    Comment


      #3
      Re: iMac mid 2010 - black screen on startup -

      Hi Piernov,
      the display does not light up but if I point a flashlight on it I can see the image on it, I replaced the backlight inverter board, thinking it was the cause, but I was wrong.
      The graphics card I replaced is one ATI Radeon HD 4670 256 MB - 661-5308
      Symptoms before replacing the graphics card were: fourth diagnostic LED was off, no backlight, no external display signal.
      I confirm no damage to the LCD connector or the components around / behind it.

      After replacing the graphics card, the external display works correctly but the internal one I can turn it on only if I send the mac to sleep and immediately afterwards I press the button again (this I have to do several times to get the ignition).
      When I succeed in the maneuver, the display remains on until the next restart.

      I forgot, when the IMAC completes startup the display lights up for only a second.
      Last edited by poldo; 10-10-2020, 12:01 PM. Reason: text added

      Comment


        #4
        Re: iMac mid 2010 - black screen on startup -

        Hi. We have repaired 3 iMACs in the past few weeks with success. Granted that they are A1312 (2011), the issue may be similar to yours.

        We too saw that the 4th POST led was remaining OFF. Confirmed with the other broken models that the video cards are to blame. We have a 9 zone SMT oven in the building and setting to 215 C and running through the oven fixed each of the video cards. Replaced the thermal pads (T-Global @ 13 W/mK @ 1.5mm thick + Arctic thermal paste for the CPU and GPU surface) is a formula that has worked for each of these repairs.

        After the above process, found that the 4th LED was still remaining off on one of the units. The display from a working iMAC confirmed that the host motherboard was no longer the issue but rather the display itself.

        Quick solution is to buy another display but that is expensive and bulky to ship.

        Next, reviewed the non-working display itself and confirmed that the LVDS cable is not torn and firmly connected on the motherboard AND the target display. All good here.

        Next removed the shield off the backside of the display - lots of black and aluminum shielding tape and a few screws.

        After this removal, located the LG logic board (aka T-con board). Note the markings and find the replacement at your favorite store on Aliexpress. Often they are about $10 USD each + shipping.

        If shopping for replacement T-con boards, be sure to chat with the vendor to confirm they will supply the exact PCB and/or guarantee the compatibility.

        We are not patient people so reviewed that there are 4 tantalum caps onboard and 2 SMD large current diodes. Tantalums are pure evil and they will die over time, hence the reason we NEVER use them in our own product designs (we are an engineering company for large OEMs). Ordered the required 33uf replacement caps from Arrow - replaced each such cap on the T-con board. About $4 USD worth of parts and time..

        Working perfectly !!

        Back to your case, your model may NOT be the LED backlight version of the display. Rather, it may be the high voltage tube backlighting. Regardless, consider to source the driver (T-con) board for your LG display if you wish to pursue this repair. There are relatively low cost independent test gear (less than $50 USD) from Aliexpress that will allow you to use a HDMI or VGA signal to test your LG panel (ie. without the use of the iMAC itself). This way you can rule out that your iMAC power supply / video card as the root cause of this failure.

        Just sharing some of our experience to date.

        Be very careful on the high voltages inside the iMAC and also the multiplier voltage power supply on the actual LG display itself.

        If you can share pictures of the labels on your LG panel, perhaps can assist more. We are about to purchase a few of the spare driver boards and test gear from China so we can quickly test the panels without the iMACs.

        Hope this helps.

        Update:

        Just Googled your 2011 iMAC details and found this:

        https://www.amazon.com/Odyson-Backli.../dp/B01LWX4KID

        That is, you have a LED backlight. So the issue may be the power supply from the host iMAC - it will be the cluster of BLACK wires and on our A1312 - it is the inverter board on the LEFT side of the machine. Look for yours. Replacement inverter power supplies should be available for < $50 USD on ebay or similar. Even on Aliexpress.

        If this fails, then it is the T-con board - BTW - on the A1312, the LG T-con board has a Maxim LCD power supply controller MAX17014A.

        You can download the reference schematic and datasheet from their website. It is very helpful to study what LG is doing for at least the A1312 model.

        Using this datasheet as a reference, we knew that we had a chance to fix the T-con board.

        If you have the time, consider to replace the tantalum caps (and diode which are cheap) before replacing the inverter power supply board.

        Take quality pix of the T-con board and post them here and see if we can debug this puppy !
        Last edited by mon2; 10-25-2020, 10:20 AM.

        Comment


          #5
          Re: iMac mid 2010 - black screen on startup -

          Hello mon2,
          first of all I wanted to thank you for the excellent exposure.
          So: I can confirm that the backlight card is O.K., as well as the video card and motherboard.
          I installed another display, as a test, and it works fine.
          So the problem is precisely the display of which I posted the photos. In my case, unfortunately, it is not possible to replace the LG card as you can see.
          The LG card has no visible damage or burns.
          I also tested the led bar with Backlight Testing Instrument and they work fine.
          Attached Files

          Comment


            #6
            Re: iMac mid 2010 - black screen on startup -

            Hi. For some reason, did not receive an alert of your posting hence the delay in this reply.

            Excellent and clear pictures

            The board you are referencing is called the T-con board in the monitor industry = timing control board.

            Later today will share a store we found on aliexpress that seems to have spares for all such LG models and from the last request, about $10 USD each and they are 100% new.

            However, as noted in my earlier post, we faced a similar issue and the root cause was the T-con board on our LG panel (iMAC A1312). The sticker / label is very important to locate the proper replacement. Or better yet, order a few replacement parts and attempt to repair this T-con board.

            Review the large black tantalum caps with "22" marked on them. These are polarized 22 uf tantalums. Tantalums in general suck. They die over time and apply a short circuit across their contacts. Just planned obsolescence.

            The parts we ordered are Kemet p/n T521V336M025ATE040
            33uf 25V (7.3 x 4.3) - these are drop in replacements for the 22uf or 33uf onboard the T-con board.

            In our repair, we replaced each of the 4 such caps onboard. If you wish, check the capacitance of your caps with a capacitance meter to see if the caps are holding their charge. In our case, they were not.

            Since you have confirmed that the power supply is good, the actual LED strips are good, the issue is down to this T-con board.

            You can buy a fresh one or attempt to repair this one.

            BTW - The same aliexpress vendor offers a tool which when paired with a specific t-con board can allow you to test any A1312 display - kind of cool. However, since you have debugged the other regions of the iMAC, feeling very strongly the issue is this T-con board. Will study your pix more later but in our case, we had a MAXIM LCD controller onboard - very helpful to review the ref designs which LG used as well to determine the details of the caps; their voltages, etc.

            I think you are very close to fixing this if you proceed.

            Hope to write back later after a bit of quick shopping...

            Quickly...the power supply is a common part from TI. See the attached ref design. You can locate the Vin = should be 12V.

            But check on Vout which likely is DEFECTIVE. Very curious to hear of your values.

            Respectively, check on the TANTALUM cap values. Most likely they are dead due to age. These are < $ 1 USD for the parts to replace from Arrow or your local shop. Be sure to check on the SIZE of the cap so you can remove and drop in solder and the VOLTAGE rating - very important.

            Kemet worked for us.

            Bye for now.
            Attached Files
            Last edited by mon2; 10-31-2020, 09:21 AM.

            Comment


              #7
              Re: iMac mid 2010 - black screen on startup -

              Hi mon2,
              always impeccable and accurate in your advice, thanks.

              I unsoldered the two tantalum capacitors and measured their capacitance (26uF) and tested the pitches (with and without capacitors):
              Pitch C121 V = 0
              Pitch C116 V = 12
              I also tested the diodes D15 and D17 present on the T-con board and they are O.K.

              I found the ones you recommended online (Kemet T521V336M025ATE040) but before ordering I wanted to complete any other checks.


              I don't understand, what measurement did you want to know regarding Vout DEFECTIVE?

              See you soon
              Paolo

              Comment


                #8
                Re: iMac mid 2010 - black screen on startup -

                Hi Pablo. So now you have confirmation that the Vboost on the T-con board is defective / not working.

                Have some questions and comments to proceed further.

                1) Check for the +3v3 rail operation on the SWB pins of the TI QFN regulator IC. You can check for the switching output voltage on inductor L1.

                Do you see +3v3 on this output rail?

                2) On your cap checking, does the cap retain the cap value with your meter? It is still worthwhile to replace these caps but in our case, we found that the cap would charge and the sink back to close to 0. On our t-con board, we replaced 4 caps and the diodes which are all very common.

                The Kemet cap was selected for the low ESR value = higher current support for the end design.

                3) Would like to know if the pins on the TI switching regulator has pins 42 & 43 shorted as it appears on the picture of the PCB. The concern being that this is not what the TI datasheet is showing in their reference schematic.

                On this note, if the pins are indeed shorted, then this component is slightly different than the datasheet from TI itself. For these reasons, if this TI component is defective (or deemed to be faulty) - then best to source the same looking part from Aliexpress - they have many pictures of the exact component. Perhaps LG had this part custom modified for their designs.

                Otherwise, pin 42 = SWO and pin 43 = AVIN and THEY ARE NOT to be shorted according to the TI website. Confused on this relationship but could be my error as there is some silkscreen on the PCB covering up these 2 pins in your picture.

                That is, if you replace this QFN part - best to source the same part from Asia and not TI since the TI (official) part does NOT short these 2 pins. Originally thought that TI has a typo (we have corrected many in the past years in their documentation) but their EVB demo kit for this component matches the datasheet - pins 42 & 43 are NOT to be shorted. Yet they appear this way in your shared pic.

                4) The vendor we have had a long chat with on Aliexpress is MACSCREEN STORE. Search for "MACSCREEN STORE ALIEXPRESS" on Google to find their store.

                Encourage you to have a chat with them to ask about a new t-con board. We are building up a list of goodies and tools from them. Can ask about yours as well on the next chat.

                Suspecting highly that replacing out this PCB should get your panel to be operational. Any A1312 T-con panel from his shop (NEW) was @ $10 USD + shipping. Be sure to share the full details of your panel and the label from this thread so they can 100% match the t-con board.

                It is very possible for this single vendor to assist you to source the replacement TI component, etc. - many shops are cool to help when they can. This way, a single shipment, single shipping fee can supply the parts for this repair.

                5) While waiting, check the capacitance of the other ceramic caps on the PCB. With your meter at the highest setting, ground on ground, RED wire on the caps. Do you see the caps charging up and retaining their capacitance value? The inspected rail should not discharge to 0 (zero).

                Please see the attachments for guidance.
                Attached Files

                Comment


                  #9
                  Re: iMac mid 2010 - black screen on startup -

                  More comments:

                  There are other diodes onboard in the SOT-23 package. Please check for their status with your meter in DIODE mode. These diodes are dirt cheap and often < $ 0.05 USD each. See if they are still ok.

                  That is, diodes D13 and D16

                  How is the cap bank @ C107 - does the meter should a high bulk capacitance at this cluster?

                  Same question @ C105 / C106.

                  Comment


                    #10
                    Re: iMac mid 2010 - black screen on startup -

                    Paolo - wanted to add another comment.

                    Be sure that the cluster of black wires is properly seated on both sides of the cable and specifically, in the proper direction. On our A1312, we observed that the pins are unique and really should have been color coded. Respectively, the cable harness is seated backwards, the t-con board will not work.

                    For us, we recall the tiny 2 locking posts on the connector housing are facing the user. This connector cannot be reversed. Perhaps ok since you mentioned that 12V is incoming to the t-con board.

                    Also, be sure of the LVDS cable seating and that the LVDS connector is still properly soldered onto the motherboard. The LVDS cable is not torn? If in doubt, source a fresh one from Asia - they appear to be relatively low cost.

                    On a past macbook repair, we found that the gold LVDS contacts were dirty from likely a coffee (Tim Horton's??) spill. Cleaned it with alcohol and the macbook was back to life.

                    While you are in there, check that D19 is also ok (along with D13 & D16). The D13 & D16 appear to be dual diodes in a SOT-23 package.

                    Comment


                      #11
                      Re: iMac mid 2010 - black screen on startup -

                      Hi mon2,
                      sorry if I only answer you now.
                      I hope I can provide you with more information as advised and requested

                      1) output voltage on the inductor L1 = 3,34V


                      2) the pins on the TI switching regulator has pins 42 & 43 shorted


                      3) other ceramic caps
                      C105-C106-C107 still to be tested


                      4) D19 ok

                      D13 and D16 : I tested these two diodes to be unsoldered and from one direction
                      emitter - collector and open, in the other direction it is closed (0.6v).
                      Should they be open? Or am I wrong?


                      5) I double checked the voltage of the pads (C116 and C121) with the capacitors repositioned and the correct results are as follows:
                      C121 = 15,38V
                      C116 = 15,41V

                      6) led driver connector pin is entered correctly

                      7) LVDS cable tested on other equipment is O.K.

                      sorry again if I made you wait but due to force majeure.
                      See you soon
                      Paolo
                      Last edited by poldo; 11-08-2020, 03:12 PM.

                      Comment


                        #12
                        Re: iMac mid 2010 - black screen on startup -

                        D13 and D16 theme song = KJE X9
                        I can't find the datasheet
                        If it was necessary to replace them, what would you recommend.

                        Comment


                          #13
                          Re: iMac mid 2010 - black screen on startup -

                          Hmm. What is the history of the video card? This range of imacs are notorious for the video card issues. Many on ebay are abandoned due to video problems. The remedy is to reflow the video card. There is a great video from "Borderline OCD" for the A1312 video card repair. Seems like everything else has been explored.

                          Comment


                            #14
                            Re: iMac mid 2010 - black screen on startup -

                            Reflow/reball is not a solution. The GPU react to the heat, it'll often resurrect the GPU for a short time but it'll fail again, there's no way to tell if it'll fail at the next reboot or after a few months. Just heating it to 200°C for a minute and a half (without flux, no reflow happening there) gives the same result. Dead GPU is dead.

                            https://logi.wiki/index.php/iMac_A13..._Graphics_card
                            OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                            Comment


                              #15
                              Re: iMac mid 2010 - black screen on startup -

                              Originally posted by mon2 View Post
                              Hmm. What is the history of the video card? This range of imacs are notorious for the video card issues. Many on ebay are abandoned due to video problems. The remedy is to reflow the video card. There is a great video from "Borderline OCD" for the A1312 video card repair. Seems like everything else has been explored.
                              Hi mon2,
                              the graphic card is new (warehouse stock) and I was able to test it with a working display with which it did not give problems.

                              Comment


                                #16
                                Re: iMac mid 2010 - black screen on startup -

                                Interesting thread that is worth a quick read:

                                https://www.badcaps.net/forum/showthread.php?t=75340

                                With a flashlight, can you confirm that the dark display is working but just not backlit?
                                Last edited by mon2; 11-15-2020, 06:27 AM.

                                Comment


                                  #17
                                  Re: iMac mid 2010 - black screen on startup -

                                  Originally posted by mon2 View Post
                                  Interesting thread that is worth a quick read:

                                  https://www.badcaps.net/forum/showthread.php?t=75340

                                  With a flashlight, can you confirm that the dark display is working but just not backlit?
                                  Hi, I had already read the discussion of the "Misterkeeks" problem, the problem he encountered is identical to mine. Unfortunately they did not come to any conclusions.

                                  I can confirm that if illuminated by the flashlight the display is working.

                                  Comment


                                    #18
                                    Re: iMac mid 2010 - black screen on startup -

                                    In my case everything has now been tested, all that remains is the display.

                                    As for the display: I tested the led line with positive result. And also the LVDS cable with success.
                                    Last edited by poldo; 11-15-2020, 10:54 AM. Reason: text added

                                    Comment


                                      #19
                                      Re: iMac mid 2010 - black screen on startup -

                                      The inverter (backlight) board sources its voltage from the main power supply.

                                      Can you carefully check the status of the LED backlight voltages (cluster of black wires) that splits to the left and right LED strips?

                                      What are the voltages at the inverter board bottom connector when the display is dark? Once you play roulette and the backlight is working, what are the voltages on this connector?

                                      You are confident that the SMD led strip connectors are not broken of each strip? This is also a common issue due to the 2-tonne LCD display that can accidentally break the SMD connector that mates with the black wires. These SMD connectors are covered with the silver (aluminum) foil tape.

                                      If these SMD connectors are loose, this could be an issue. On this note, please be careful when inspecting this area as to not create a new problem if the SMD connectors are already solid. There are a number of youtube videos on this subject.

                                      If you feel comfortable, turn on the unit -> wait for the chime and gently (very gently) wiggle the led strip areas (one on the left; another on the right) - each at the bottom of the display. Do you see any change on the backlight?

                                      However, if you have confirmed that the panel lights up with another tool - which I think you have said, then perhaps these connectors are not the issue.

                                      Comment


                                        #20
                                        Re: iMac mid 2010 - black screen on startup -

                                        Hi,
                                        here I am again, still feverish, but anxious to understand what the hell is wrong with this screen.
                                        In recent days, despite myself, I have been able to repeatedly try the game of roulette but unfortunately without results.

                                        At the moment I can only give you information on the status of the LED backlight voltages (cluster of black wires) only when the display is dark:

                                        PIN1 = 0,017V
                                        PIN2 = 12V
                                        PIN3 = 0,006V
                                        PIN4 = 12V
                                        PIN5 = 0,018V
                                        PIN6 = 12V

                                        Comment

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