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Hanns-G HH251 Does not Power Up.

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    #1

    Hanns-G HH251 Does not Power Up.

    Thank you guys for the wonderful site and willingness to help. I used the information to recap and repair a 19" LCD with obviously bad caps and got a great deal of satisfaction when the screen came back to life.

    This board seems a bit trickier.
    I Have done a little probing on the board and here is what I have come up with.

    Monitor will not Turn on but the switch checks good.
    Capacitors all look good but they are all cheap Taicon.
    I have 110 AC to the first Transformer and 65v out
    I have 45 v out of the second transformer with 65v in.
    The power connector that goes to the 2nd board has no power out 12vdc or 5vdc.

    I guess what you could help with is to give me the next logical things to check and how. Should I recap the board? Can caps cause a complete loss of power?

    Should I pull the Mosfets? off the heatsinks and replace them. I have checked them in circuit and a couple appear to be shorted.

    Picture of the Power Supply board is attached.

    Also is there a source for a service manual for this beast.

    Thanks in advance for your help
    Attached Files
    Last edited by ZappedAgain; 12-14-2011, 11:57 PM. Reason: Added pic of back
    Tags: None
    #2
    Re: Hanns-G HH251 Does not Power Up.

    1) Thank you for a clear focused picture using the manage attachment button. Thanks also for punctuation, paragraphs, and not the poor quality crap we have had to deal with lately.

    2) What is the DC voltage across the largest capacitor (just under the word Primary)? It should be around 165 V DC if working properly.

    3) What is the DC voltage of the cap (looks like C120) just above JP103? Is it steady or fluctuating?

    4) We will probably need a clear focused pic of the backside as well. We are looking for possibly a 8 pin IC that is the SMPS chip.
    Last edited by retiredcaps; 12-14-2011, 11:51 PM. Reason: added C120 and look for SMPS chip
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      #3
      Re: Hanns-G HH251 Does not Power Up.

      5) F240 and F260 are fuses. A good fuse should measure less than 1.0 ohms.

      6) Is that a solder blob on ZD260 and R263? Piece of straw?
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        #4
        Re: Hanns-G HH251 Does not Power Up.

        Originally posted by retiredcaps View Post
        6) Is that a solder blob on ZD260 and R263? Piece of straw?
        Looks more like a strand of the white glue stuff. Same thing on the coil near the AC input fuse (above the yellow block cap)

        Comment

          #5
          Re: Hanns-G HH251 Does not Power Up.

          7) What is part number U101 on the backside? This should be the SMPS chip.
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            #6
            Re: Hanns-G HH251 Does not Power Up.

            For Retired Cap

            1) I have been accused of many things but never good punctuation.

            2) What is the DC voltage across the largest capacitor (just under the word Primary)? It should be around 165 V DC if working properly.

            DC Voltage is 167v and steady

            3) What is the DC voltage of the cap (looks like C120) just above JP103? Is it steady or fluctuating?

            Jumps between 8vdc and 13vdc

            4) We will probably need a clear focused pic of the backside as well. We are looking for possibly a 8 pin IC that is the SMPS chip.

            5) F240 and F260 are fuses. A good fuse should measure less than 1.0 ohms.

            I am reading 2.9 ohms across both. I need to calibrate my meter leads shorted reads 1.8 ohms.

            6) Is that a solder blob on ZD260 and R263? Piece of straw?

            It was a strand of Glue. (since Removed)

            I added it to my original post.

            Comment

              #7
              Re: Hanns-G HH251 Does not Power Up.

              Originally posted by ZappedAgain View Post

              3) What is the DC voltage of the cap (looks like C120) just above JP103? Is it steady or fluctuating?

              Jumps between 8vdc and 13vdc
              That small cap could be the root cause. It should be a steady voltage. The SMPS IC Vcc pin probably is tied directly to this cap. If the cap DC voltage is fluctuating, the SMPS won't startup properly.

              Generally, we recommend replacing all electrolytic capacitors (with something like Panasonic FR/FM/FC series) on the board except the largest which rarely, but not never, fails.

              For the purposes of finding root cause, I would like you to replace JUST C120. If your monitor works, then recap the rest.
              Last edited by retiredcaps; 12-15-2011, 12:43 AM.
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                #8
                Re: Hanns-G HH251 Does not Power Up.

                Originally posted by ZappedAgain View Post
                I am reading 2.9 ohms across both. I need to calibrate my meter leads shorted reads 1.8 ohms.
                Either calibrate or your probes are frayed internally and/or your battery is dying which causes inaccurate readings.
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                  #9
                  Re: Hanns-G HH251 Does not Power Up.

                  Originally posted by retiredcaps View Post
                  7) What is part number U101 on the backside? This should be the SMPS chip.
                  Wow. that is tiny print for these old eyes.

                  Best I can tell it is 131427448-40T

                  Comment

                    #10
                    Re: Hanns-G HH251 Does not Power Up.

                    Originally posted by ZappedAgain View Post
                    Best I can tell it is 131427448-40T
                    Is it written like

                    1314
                    27448
                    40T

                    or some variation of the above?
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                      #11
                      Re: Hanns-G HH251 Does not Power Up.

                      Originally posted by retiredcaps View Post
                      Is it written like

                      1314
                      27448
                      40T

                      or some variation of the above?
                      Written Just like this

                      131427448-40T

                      Comment

                        #12
                        Re: Hanns-G HH251 Does not Power Up.

                        Originally posted by ZappedAgain View Post
                        Written Just like this

                        131427448-40T
                        Wow, all that fit on the 6 pin IC? Anyway, I had no luck finding a datasheet for it so replace that small startup cap and retest your monitor.

                        I'm guessing it is a 22uF or 47uF 50V cap.
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                          #13
                          Re: Hanns-G HH251 Does not Power Up.

                          Originally posted by retiredcaps View Post
                          Wow, all that fit on the 6 pin IC? Anyway, I had no luck finding a datasheet for it so replace that small startup cap and retest your monitor.

                          I told you it was tiny print

                          I'm guessing it is a 22uF or 47uF 50V cap.
                          47uf 50v

                          I will get a full set of caps ordered and post after I replace.

                          I will start with c120 and see if it fires up.

                          Thanks tons for your help so far.

                          Comment

                            #14
                            Re: Hanns-G HH251 Does not Power Up.

                            Originally posted by retiredcaps View Post
                            7) What is part number U101 on the backside? This should be the SMPS chip.
                            I took a little alcohol and cleaned the top of U101 then took an extreme closeup with my scanner. Revealed a whole other line of numbers.

                            Image is attached
                            Attached Files

                            Comment

                              #15
                              Re: Hanns-G HH251 Does not Power Up.

                              Originally posted by ZappedAgain View Post
                              I took a little alcohol and cleaned the top of U101 then took an extreme closeup with my scanner.
                              That helps alot. I love helping people who do some extra work.

                              Datasheet is at

                              http://pdf1.alldatasheet.com/datashe.../SG6741SZ.html

                              Pin 7, Vdd, requires at least 15.5 V (min) to start with 16.5 (typical), and 17.5 (max). So 8 to 13V DC from C120 won't be enough to start the SMPS.
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                                #16
                                Re: Hanns-G HH251 Does not Power Up.

                                This is an excellent job by all concerned. I'd like to add a few points.

                                It is likely that replacing C120 will bring the monitor back to life. Replacing the rest of the caps as planned is an excellent approach.

                                In the event this does not fix the problem, in this design the SMPS controller generates the startup voltage internally. We have seen a number of failures of ICs using this approach. The SG6741SZ is available on eBay.

                                Another potential problem is a shorted output diode in the SMPS, or other secondary short.

                                PlainBill
                                For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                                Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                                Comment

                                  #17
                                  Re: Hanns-G HH251 Does not Power Up.

                                  Originally posted by PlainBill View Post
                                  The SG6741SZ is available on eBay.
                                  findchips says

                                  http://www.findchips.com/avail?part=SG6741SZ

                                  mouser has 2,137 for 78 cents.

                                  You can try measuring the resistance between Vdd and GND to see if it is shorted while waiting for the caps to arrive.
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                                  Comment

                                    #18
                                    Re: Hanns-G HH251 Does not Power Up.

                                    Hi all,

                                    I know this thread is a few years old, but i was wondering if replacing c102 cap fixed the problem and also if any one knows what c102 is as i have the same monitor and the same symptoms, but c102 is melted so cant tell wheat the value is.


                                    Thanks for any help

                                    Comment

                                      #19
                                      Re: Hanns-G HH251 Does not Power Up.

                                      I also would like to know a: the value of C120 and b: did it fix the problem.

                                      I have a 3 yr old HH251 and the other day it just went black after a couple seconds (power LED stays green). Power it off and restarting does the same thing every time.
                                      I have taken the monitor apart and visually the caps look fine (none swollen or leaking).

                                      Sam

                                      Comment

                                        #20
                                        Re: Hanns-G HH251 Does not Power Up.

                                        Carry out the '2 secs to Black' tests ,as shown in the Sticky

                                        Comment

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