Bush ltf22m4 mosfet replacement

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  • Studley
    Member
    • Feb 2013
    • 18
    • Uk

    #1

    Bush ltf22m4 mosfet replacement

    Can anyone help me with a replacement mosfet. The attached photo shows the mosfet I'm trying to get hold of. The tv is a Bush LTF22m4 the board number is:- msdv 3206-zc01-01 (b)

    Thanks in advance.
    Attached Files
  • selldoor
    Slow Learner
    • Dec 2010
    • 7870

    #2
    Re: Bush ltf22m4 mosfet replacement

    Are you sure its a mosfet and not a 1084 votage regulator?

    test is here
    https://www.badcaps.net/forum/showthread.php?t=22231
    Last edited by selldoor; 02-15-2014, 05:10 PM.
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment

    • Studley
      Member
      • Feb 2013
      • 18
      • Uk

      #3
      Re: Bush ltf22m4 mosfet replacement

      Thanks selldoor, that does seem to be the case. Is this a case of searching the 1084 number and replacing with the same or are there different variants of voltages?

      Comment

      • selldoor
        Slow Learner
        • Dec 2010
        • 7870

        #4
        Re: Bush ltf22m4 mosfet replacement

        Do you need to replace it? if you were testing as a mosfet you need to test as a voltage regulator? or has it burnt up and this is not your board?
        I cant tell from the picture as you have cut it off but as it doesnt indicate a voltage eg 1084-33 1084-5 it is probably an adjustable - it will have small resistors between the adjust leg and vout leg.
        The 1084 is a hefty LDO and replacement needs to be 5A there are a number of
        makes of 1084 but we have looked before and cant find who makes the one with the ( כ|| ) logo. They should all be a similar size but if you can find a datasheet for the one you decide on best just to check it going to fit.
        Oh and you also need the same package with 3 full legs or 2.5 legs again I cant quite tell from the picture.
        Last edited by selldoor; 02-16-2014, 03:32 AM.
        Please upload pictures using attachment function when ask for help on the repair
        http://www.badcaps.net/forum/showthread.php?t=39740

        Comment

        • Alastair E
          Chief Womble
          • Mar 2013
          • 1963
          • U.K.

          #5
          Re: Bush ltf22m4 mosfet replacement

          Maybe we need to go back to basics....

          That reg could well be just fine, O/P mistakes it for MOSFET.....

          What is wrong with the set? Symptoms, and a picture of the results on the screen--If any!
          TELEFIX

          How PLASMA SCREENS WORK, X-SUS and Y-SUS what they do--
          http://www.irf.com/technical-info/appnotes/an-1088.pdf
          PLEASE DO NOT EMAIL ME PRIVATELY FOR REPAIR ADVICE. QUESTIONS BELONG ON THE FORUM!

          Comment

          • Studley
            Member
            • Feb 2013
            • 18
            • Uk

            #6
            Re: Bush ltf22m4 mosfet replacement

            More information; The tv powers up and works fine on hdmi and av inputs. The problem is with the DTV. When selected, the channel comes on with good sound and picture but after about 30 seconds picture freezes and the sound ceases and doesn't come back on unless you turn off and back on again. On investigation of the board I managed to burn my finger on that particular voltage regulator. Its also situated in the area of the tuner which has led me to conclude its the culprit at fault.

            Comment

            • selldoor
              Slow Learner
              • Dec 2010
              • 7870

              #7
              Re: Bush ltf22m4 mosfet replacement

              I said it was a beast - they are supposed to work hot 5 amps is hot some of these work at 300 ma.
              You really need to test it - I gave you the link..
              I suppose it could be extra hot if the caps around it are bad making it work harder. I say test it first then consider replacing the caps
              Please upload pictures using attachment function when ask for help on the repair
              http://www.badcaps.net/forum/showthread.php?t=39740

              Comment

              • Studley
                Member
                • Feb 2013
                • 18
                • Uk

                #8
                Re: Bush ltf22m4 mosfet replacement

                Will get and test it later today and give the voltages. Just for your info, I have attached a larger view of the pcb. Thanks for all your help so far.
                Attached Files

                Comment

                • selldoor
                  Slow Learner
                  • Dec 2010
                  • 7870

                  #9
                  Re: Bush ltf22m4 mosfet replacement

                  Ok - test the other one as well. Did it not n=seem as hot? what make series of caps are they? The one above looks like a changii but the other two cant tell.
                  Please upload pictures using attachment function when ask for help on the repair
                  http://www.badcaps.net/forum/showthread.php?t=39740

                  Comment

                  • Studley
                    Member
                    • Feb 2013
                    • 18
                    • Uk

                    #10
                    Re: Bush ltf22m4 mosfet replacement

                    Have now measured the voltages of both the regulators. The suspect one is;- pin1, 6.60v pin2, 7.85v pin3, 20.01v
                    The one adjacent is;- pin1, 3.75v pin2, 4.99v pin3, 7.82v (this one is the coolest)
                    The caps adj are made by Aishi which I have changed out as some of the 470uf were reading just over 500uf. The others I have also changed. This has made no difference to the tv cutting out when on DTV.

                    Comment

                    • tom66
                      EVs Rule
                      • Apr 2011
                      • 32560
                      • UK

                      #11
                      Re: Bush ltf22m4 mosfet replacement

                      What happens to suspect's pin voltages when fault occurs?
                      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                      Comment

                      • Studley
                        Member
                        • Feb 2013
                        • 18
                        • Uk

                        #12
                        Re: Bush ltf22m4 mosfet replacement

                        The voltages don't seem to change.

                        Comment

                        • tom66
                          EVs Rule
                          • Apr 2011
                          • 32560
                          • UK

                          #13
                          Re: Bush ltf22m4 mosfet replacement

                          Do you have any freeze spray? I would try cooling it with that, see if you can get picture/sound to come back. If you don't have any, PoundLand have cans 200ml for £1 which is cheaper than ebay.

                          I think that's an 8V regulator, for the audio circuit or such, the other regulator then uses the 8V, dropping it down to 5V for some other logic.

                          Very odd to see a 20V rail in a 22" TV, are you sure about that?
                          Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                          For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                          Comment

                          • Studley
                            Member
                            • Feb 2013
                            • 18
                            • Uk

                            #14
                            Re: Bush ltf22m4 mosfet replacement

                            Will have to buy some spray in the week. Glad you said 200ml cans are a pound because the most common question asked in poundland is "how much"? lol. The reason for the 20v I think is down to the mains adapter is rated at 20v output DC.

                            Comment

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK

                              #15
                              Re: Bush ltf22m4 mosfet replacement

                              Ah that makes some sense, 12V is most common. If so the heat in that chip is not at all unexpected, does TV have a USB port? If you attached 200mA load to USB port (typical when flash drive playing movie file) then the 8V regulator (the 5V ties into it) would dissipate 2.4 watts -- which would put it around 100°C. Just an example. Other loads would heat it up further.
                              Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                              For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                              Comment

                              • selldoor
                                Slow Learner
                                • Dec 2010
                                • 7870

                                #16
                                Re: Bush ltf22m4 mosfet replacement

                                Looks like we are looking elsewhere for the problem. Can you post full pictures of your boards
                                Please upload pictures using attachment function when ask for help on the repair
                                http://www.badcaps.net/forum/showthread.php?t=39740

                                Comment

                                • Studley
                                  Member
                                  • Feb 2013
                                  • 18
                                  • Uk

                                  #17
                                  Re: Bush ltf22m4 mosfet replacement

                                  Tom, I think i've just spotted the problem. I bought this tv from a guy who said the tv kept freezing and couldn't put up with it any more. You saying to me about it being strange having 20v at the regulator, I just double checked and yes the power adapter is 20v but noticed on the back of the tv, it says 12v dc input 3amp!! Conclusion, this guy has accidentally pluged the wrong power adapter by mistake thus creating this problem. The adapter he gave me is a Lenovo, (which I guess is for a computer?). Going to see if i can find something rated at 12v 3amp and give it a try. Can't believe this!!!

                                  Comment

                                  • selldoor
                                    Slow Learner
                                    • Dec 2010
                                    • 7870

                                    #18
                                    Re: Bush ltf22m4 mosfet replacement

                                    Sounds like that would do it- good catch.
                                    Please upload pictures using attachment function when ask for help on the repair
                                    http://www.badcaps.net/forum/showthread.php?t=39740

                                    Comment

                                    • Studley
                                      Member
                                      • Feb 2013
                                      • 18
                                      • Uk

                                      #19
                                      Re: Bush ltf22m4 mosfet replacement

                                      Hi selldoor and Tom, have just found a 13v adapter and tv is fine.
                                      So lesson for today.....get right back to basics, even down to other people giving out the wrong information. I can't tell him he plugged the wrong adapter in.... only gave him £20 for the tv.

                                      So whats he using the Bush adapter for?

                                      Comment

                                      • tom66
                                        EVs Rule
                                        • Apr 2011
                                        • 32560
                                        • UK

                                        #20
                                        Re: Bush ltf22m4 mosfet replacement

                                        A friend had this problem before. Received a new 24" Bush LED TV for signing up to one of those life insurance things -- Argos direct -- inside the box was a 9V DC adapter for a cordless phone! The power light just flashed. Found a 12V adapter and it worked fine.

                                        TBH, I'm surprised the 20V didn't blow anything up!
                                        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                        Comment

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