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ONN 100012588 Has fluctuating Voltage on PSU 12v

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    ONN 100012588 Has fluctuating Voltage on PSU 12v

    Hello all got another TV here im puzzled by. why cant they all be easy fixes that just need a little love and some tape???

    anyway i go to this guys house to look at an ONN 100012588
    this is my first time looking at one of these brand of TV's.
    TBH i have low expectations because i see ONN as the cheap walmart brand that suddenly popped up selling the cheapest version of all kinds of tech things. and someone sent me a ONN flash drive with some data on it with some recordings they wanted me to check out and it immediately broke and corrupted the data and i was unable to do anything to salvage either the data or the drive as a usable device. so already i think this brand may be cutting corners!

    anyway back to the story:
    i show up and sure enough the TV shows no signs of life.
    i really need to start taking better notes because i cant say for sure if it had a blinking red LED or not but at any rate the TV would not turn on.
    so i take the back off and test the backlights. there are 2 separate 2 wire connectors that go to the LED strips and i am able to get both of them to light up so i declare "its not the backlights!"
    moving on, i plug in the Power supply without the MB attatched to see if maybe it has one of those nice "self power on and backlight test" features that make things easy. nope it doesnt have that. nothing happens.
    so i test voltages and notice that the 12v is not a steady 12v, its swinging between 10.5 and 12v or so.
    i also see that there is a marking on the board for 5VSB but it has no voltage on it.
    So i say "Looks like a bad PSU!"
    i have never seen voltage fluctuating like this on a GOOD PSU!
    so the new PSU comes in, and i plug it in (but not to MB), and i notice that it ALSO has this fluctuating 12v and no 5VSB ... so now im thinking...wait. is this NORMAL?
    or did the guy send me another PSU with the same issue?
    cross my fingers and plug in the MB,
    Notice that the 12v becomes stable
    The TV turns on, stays on. has good picture. everythings fine! turn on and off a few times...let run for a few minutes...
    call it good...dont question it!
    but in the back of my mind i feel like i will be back and sure enough just one week later he calls to say the TV is dead again


    so i come back and sure enough the tv wont turn on. this is when i notice for sure that the red LED is just blinking faintly over and over...
    i notice that the PSU voltage is fluctuating again even with the main plugged in. but also that it dips real low when the main is plugged in. down as low as 5v. and this fluctuating seems to coincide with the red LED blinking. basically the MB is trying to boot up, so initially the LED comes on but then it quickly fails and so the voltage drops and the LED turns off, and then it tries again over and over.
    it sure seems like it would be because of the fluctuating voltage on the PSU causing this, but we already changed the PSU and it didnt fix the problem so we go ahead and order the Main Board.

    sadly, the mainboard comes in and doesnt change the situation at all.

    so now im left a bit confused.
    did the guy send me a PSU with one week of life left in it?
    is the TV breaking from some other reason due to the clients house or use situation?
    do i have two good power supplies but was actually sent a bad mainboard?
    is that voltage fluctuation on the PSU normal?
    am i kind of losing my mind on this one? yes! and my ass too!
    between my time and his money a lot has been invested so i cant just give up! someone out there please flip my coat in the right direction. has anyone worked on these ONN sets and can report about the fluctuating voltage?

    oh another wrinkle in the plot. come to find out the PSU that i ordered... the seller doesnt accept returns! how did i not see that before ordering?


    i sent the ebay seller a message asking if they were serious about the no returns, and also told them about the fluctuating voltage.
    They do have a few of these tvs apparently, i see them still selling parts for it. Maybe they will actually go check and report back to me but somehow i doubt it!

    if i cant get some answers somehow, i may end up buying another PSU! I will be crossing every bone in my body at that point. help me out of this jam, my friends! if you can!
    Attached Files
    Last edited by triplefour; 09-14-2022, 07:52 PM.
    Don't fear the repair...

    #2
    Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

    https://www.badcaps.net/forum/showth...ight=100012588
    PS i read this thread, the only other one here on this TV and i do not have this similar problem, but i can confirm that this board holds a nasty charge in 2 other places besides the primary filter caps. those PFC discharge nicely over time but the other 2 dont, and hold for hours. and i got bit once, by handling the board when i thought i had discharged everything. careful!
    Don't fear the repair...

    Comment


      #3
      Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

      can try to verify backlights and powerboard with stand alone powerboard test, unhook cable from powerboard to mainboard, use three 1k resistors to jump pson, bk, adj, to +5vsb, plug power cord into powerboard, see if backlights come on and stay on, can check if you have steady voltages also.

      Comment


        #4
        Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

        i did that. the backlight would only flash on for a second then go off. voltages do not stabilize. but with backlight tester, backlights test fine. backlights shouldnt matter though. even with backlight disconnected, the main should be able to boot up...but it just keeps blinking red light in time with the fluctuating voltage as it drops to around 5v and then back up to 12 over and over. power supply fluctuates on its own but then fluctuates even lower when MB is connected. no response from power button of course.

        i have taken the main and PSU boards, and left the TV and backlights there so i cant do tests on BL, only on PSU and MAIN without going over to the guys house...which isnt close

        how do we know to give 5v to adj? is that just what it usually is on other tvs?
        Last edited by triplefour; 09-15-2022, 12:41 PM.
        Don't fear the repair...

        Comment


          #5
          Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

          ok, I think if you use those jumpers with just the powerboard and nothing else connected and you still have fluctuating readings, like even the standby is fluctuating, then must be a powerboard issue, can be bad solder joint/s, bad capacitor/s, bad voltage regulating diode etc., simple things first, look over the joints, check all diodes and resistors, suppose it could also be bad backlights blowing out each powerboard that you try??

          Comment


            #6
            Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

            There is no 5vsb. This is one of those boards that doesn't have it. So I have to inject 5v with a little USB adapter I canibalized. I don't see how it could be backlight problem when they test OK with the tester. I am trying again to put 5v to all three of those pins but I noticed something. I connect 3 wires I made with needle points on each end and a 1k resistor in the middle. All pins read 5v after the resistor as they should. But when I plug them into the board, the voltages drop. Measuring I get 2.8v on PSON, 3.88v on BK, and 3.99v on ADJ. I'm "giving" each pin 5v but they are pulling the voltage down. What is happening here? This is without giving the board AC. When plugging the board in, the voltages rise a little. Now I see 5v on ADJ and 4.6v on PSON and BK. But i still have the swinging voltage.
            Last edited by triplefour; 09-15-2022, 01:21 PM.
            Don't fear the repair...

            Comment


              #7
              Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

              connector 201 in your pictures has +5vsby, are you saying it's not connected or mislabeled?

              Comment


                #8
                Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                do you get your other correct voltages 12v etc? when jumped.
                Last edited by nomoresonys; 09-15-2022, 01:33 PM.

                Comment


                  #9
                  Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                  are you getting about 400 volts on the main filter cap/s?

                  Comment


                    #10
                    Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                    Originally posted by triplefour View Post
                    There is no 5vsb. This is one of those boards that doesn't have it. So I have to inject 5v with a little USB adapter I canibalized. I don't see how it could be backlight problem when they test OK with the tester. I am trying again to put 5v to all three of those pins but I noticed something. I connect 3 wires I made with needle points on each end and a 1k resistor in the middle. All pins read 5v after the resistor as they should. But when I plug them into the board, the voltages drop. Measuring I get 2.8v on PSON, 3.88v on BK, and 3.99v on ADJ. I'm "giving" each pin 5v but they are pulling the voltage down. What is happening here? This is without giving the board AC. When plugging the board in, the voltages rise a little. Now I see 5v on ADJ and 4.6v on PSON and BK. But i still have the swinging voltage.
                    Without AC the board is only getting power from your USB adapter. 5v 500mA, it's not enough.

                    Comment


                      #11
                      Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                      Originally posted by diif View Post
                      Without AC the board is only getting power from your USB adapter. 5v 500mA, it's not enough.
                      but wouldnt this still be the same situation even with AC plugged in? those pins normally have no voltage on them, and the only voltage they are getting is still only coming from my usb adapter is it not? should be same voltage and current in my mind...

                      so why the change?


                      and to answer a previous question yes i believe the 5vsb is mislabeled on the board. there is no wire from the connector that goes to it, so it is not used by the mainboard. no idea why it is marked there. maybe another version of this PSU DOES have 5vsb
                      Don't fear the repair...

                      Comment


                        #12
                        Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                        Originally posted by nomoresonys View Post
                        do you get your other correct voltages 12v etc? when jumped.
                        the only voltage rail there is is the 12v and it is there even in standby...but it goes up slightly (about a volt) when jumped on.

                        are we in agreement that a voltage should never be swinging like this?
                        the guy sent me a bad PSU with the same problem?
                        no idea how it fixed the tv for a week tho...
                        Don't fear the repair...

                        Comment


                          #13
                          Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                          This power supply is an always on power supply, in standby the pfc circuit is off and the main switching ic is likely in burst mode, that is why the voltage on the 12v line is low, anywhere from 8 to 10 volts is fine in standby. The main board has regulators that can handle the lower voltage and supply the +5v or +3.3v for the microprocessor.
                          When the power button is pressed, 3.3~5v is supplied to the power supply (PSON) to tell the main smps ic to go full on and also turn on the pfc section, that is when the 12v is at full and also the the supply for the backlights is full voltage.

                          If the PSON does not change when the power button is pressed, the likely suspect is the main board.

                          Comment


                            #14
                            Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                            test the tcon in stand alone buy supplying 12 and then test sub voltages..

                            Comment


                              #15
                              Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                              Originally posted by R_J View Post
                              This power supply is an always on power supply, in standby the pfc circuit is off and the main switching ic is likely in burst mode, that is why the voltage on the 12v line is low, anywhere from 8 to 10 volts is fine in standby. The main board has regulators that can handle the lower voltage and supply the +5v or +3.3v for the microprocessor.
                              When the power button is pressed, 3.3~5v is supplied to the power supply (PSON) to tell the main smps ic to go full on and also turn on the pfc section, that is when the 12v is at full and also the the supply for the backlights is full voltage.

                              If the PSON does not change when the power button is pressed, the likely suspect is the main board.
                              but what about the swinging voltage? is that normal for this PSU? even when i put PSON and BK to 5v i get this swinging voltage.
                              to recap: i originally diagnosed as bad PSU, replaced the PSU and the tv was fixed for one week. voltages were swinging without MB plugged in but when MB plugged in, voltages were stable. now they swing even with mainboard plugged in. ordered new Mainboard and it did not change the situation at all.
                              Last edited by triplefour; 09-17-2022, 02:54 PM.
                              Don't fear the repair...

                              Comment


                                #16
                                Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                                Then ok, let's suppose both Power boards are faulty, then try replace the optocoupler and the shunt regulator on the under side, it is connected to optoc. and marked 431.. a good replacement for example AS431..

                                Comment


                                  #17
                                  Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                                  .
                                  Last edited by R_J; 09-17-2022, 06:23 PM.

                                  Comment


                                    #18
                                    Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                                    My instructions were to unplug mainboard, which he did.

                                    Comment


                                      #19
                                      Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                                      My money is on bad backlights.
                                      Last edited by R_J; 09-17-2022, 06:24 PM.

                                      Comment


                                        #20
                                        Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

                                        Originally posted by R_J View Post
                                        My money is on bad backlights.
                                        But the psu should be able to power on the main without backlights or tcon attached... not just blink like crazy and fluctuate voltage, right ? Plus I tested the backlights. I know my tester only puts out a small current so it can give a false positive...but thats pretty rare.
                                        Don't fear the repair...

                                        Comment

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