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    #1

    Fujitsu Siemens C383FA

    Hey there, totally new to the forums and in fixing electronics in general!
    I'm studying telecommunications at the Uni but I had very few hours of practice with electronics and stuff ... so I'm kind of inexperienced.


    Now to the actual problem regarding this monitor. One day after electricity jump both my samsung 740B and FS just refused to turn on.
    - I was able to successfully repair the Sammy (had to replace 3x caps and a blown fuse), even though I was unable to find a proper fuse to stick it into there.
    - On the Siemens unit even the light on the front panel wouldn't come on, so I knew it was something related to power.

    This unit has this kind of PSU PCB that is located in the monitor's stand.



    Now, after taking it apart and inspecting it seems that the big SAMXON 120uF 400V capacitor has a bulged top.
    All the other caps are SAMXON as well and seem to be OK.
    Also the glasstube fuse rated 6A/250V is broken.

    The black thing besides the big capacitor and the coil appears to be dead as well.
    The textolite has turned yellowish-brown underneath the board, but the mosfet (is this even a mosfet?) responds to multimeter Ohm readings.


    May be I'm testing it wrong, I just have no proper skill yet, may be someone could point me in the right direction?

    As of yet my questions are the following:

    1. How do I test the mosftet (??) with a multimeter to determine wether it's dead or not? It has 4 pins I believe, haven't desoldered it yet.
    2. Can I replace the fuse with any 6A rated or it should be the glass tubing one?
    3. Initially the big capacitor was wrapped in some kind of isolation that looks like shrinking tube of some sort, it this obligatory to put it on after replacing or it's just there for some odd reason ?


    P.S. Excuse my lame english, it's not my mother tongue and thanx in advance !
    Tags: None
    #2
    Re: Fujitsu Siemens C383FA

    that black box is the bridge rectifier. looks like it got pretty damn hot..

    the fuse.. well.. replace it with a fuse rated for 250V and you should be set. just by the way.. its a 1.6A fuse... not 6A :O

    the heatshrink tubing around the cap is for insulation. should be put back on the new cap (tape the open part shut) or redone with a new heatshrink tube..

    edit: i've got an older version of this monitor (so old that it's labeled Siemens Nixdorf instead of Fujitsu Siemens).

    i had some glitchiness going on on the screen. wavy lines and stuff like that.
    the output caps were visibly OK, but dried out. so i replaced ALL caps in that powersupply (don't forget the tiny one next to the transformer). lines went away..

    just by the way.. i mean.. you're in there anyways
    Last edited by Scenic; 07-21-2010, 08:23 AM.

    Comment

      #3
      Re: Fujitsu Siemens C383FA

      Originally posted by Scenic
      that black box is the bridge rectifier. looks like it got pretty damn hot..
      yeah, it pretty much fried the board around it. but how do i actually verify if it's operational?
      Originally posted by Scenic
      the fuse.. well.. replace it with a fuse rated for 250V and you should be set. just by the way.. its a 1.6A fuse... not 6A :O
      Oh, my bad, I even thought to myself for a moment that even 3A is a high rating but 6A ... oO yeah 1.6A ... at least I have those around.

      Originally posted by Scenic
      i had some glitchiness going on on the screen. wavy lines and stuff like that.
      the output caps were visibly OK, but dried out. so i replaced ALL caps in that powersupply (don't forget the tiny one next to the transformer). lines went away..
      Mine hasn't suffered from these when it was functional. As a matter of fact I have some 1000 uF 25V rated left over from Sammy repair, those on the Siemens PCB are rated 1000 uF 16V. Will 25V still be ok ?

      Comment

        #4
        Re: Fujitsu Siemens C383FA

        Ok desoldered the components.

        All the electrolytic stuff from the largest capacitor was underneath the actual component, covering the PCB (go rubbing alcohol! )
        The fuse is rated 250V 1.5A not 1.6A as stated on the board, but oh well .. Ive got some 1.6 spares around
        The rectifier left a deep burn marks on the PCB. Its a KBP205G and I seem to be unable to find a replacement at my local stores (I happen to reside in Europe, Latvia)... any other options are possible?

        Comment

          #5
          Re: Fujitsu Siemens C383FA

          A bridge rectifier is basically just 4 diodes, so test them as such.

          take a multimeter and switch it to ohm.
          test between one of the “~” and “+” legs.
          You should get an almost-zero reading in one direction, and when you reverse the test probes (on the same 2 pins), you should get an almost infinite reading.

          Repeat the same tests with the other legs.

          if it doesn't make a difference what you connect to where (reversing multimeter cables) or if it always reads near zero (shorted) or infinite (open) between pins, it's bad.


          as for the caps.. if they physically fit (and they're good brand low esr caps), they're ok. the voltage on caps is just the maximum they can handle.

          edit: KBP205G is a 2A bridge rectifier. replacing it with a more beefy one (4A for example) shouldn't be a problem (if it physically fits.. again)
          Last edited by Scenic; 07-21-2010, 09:54 AM.

          Comment

            #6
            Re: Fujitsu Siemens C383FA

            Thank you very much yet again, it was very informative!
            Well, it gives 0.0x both ways if probing "~" and "+" pins, so it fried after-all (oh, how predictable this is ... considering the burn marks it left).

            Can you, by any chance, suggest any rectifier with the given 4Amps ?
            Will THIS kind of bridge rectifier work? Oh, and, assuming the fuse is 250V rated the rectifier should be no way more than this, right ? Somewhat around 250-ish V ?

            Comment

              #7
              Re: Fujitsu Siemens C383FA

              the original one was rated for 400V... shouldn't go lower than this..

              if i remember correctly, the rectified voltage coming out is 1.4 times the input voltage.
              so for example 230V * 1.4 = 322V .. (that's also why there's usually a 400-450V primary cap)

              the fuse is before the rectifier, so it would "only" get around 230-240V or 115-125V (depending on your location)..

              Comment

                #8
                Re: Fujitsu Siemens C383FA

                OK ordered new parts, will update as soon as I get and install them.

                - Jamicon (?) 120uF 400V cap
                - Jamicon 47uF 35V cap
                - Jamicon 1000uF 16V caps x2
                - KBP207G diode bridge rated 2A / 1000V
                - Micro fuse fast tr5 1.6 (RFS_1.6)

                These are being shipped from Sweden so itll take roughly 5 days to arrive here.

                Comment

                  #9
                  Re: Fujitsu Siemens C383FA

                  Jamicon?

                  Jamicon don't make capacitors suitable for power supplies as far as I'm aware.

                  Comment

                    #10
                    Re: Fujitsu Siemens C383FA

                    oh snap, am I screwed ?

                    Comment

                      #11
                      Re: Fujitsu Siemens C383FA

                      Originally posted by TimeWalker
                      oh snap, am I screwed ?
                      They will probably work okay, but for switch mode power supplies, you want low ESR type caps.

                      For your next order, folks here will give you plenty of feedback if you say something like ...

                      Can someone do a sanity check to make sure company xyz cap type abc series zz works in a switch mode power supply for a computer LCD monitor?
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                      We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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                      Comment

                        #12
                        Re: Fujitsu Siemens C383FA

                        Yikes Jamicon those are the caps I usually shotgun on sight.

                        Any low ESR series from Chemicon, Panasonic, or Nichicon will suffice.

                        Panasonics FCs or FMs for example would work well on any PSU secondary.

                        Check the switching FET too usually the fuse blowing signifies a problem on the primary side the big semis that blow from surges are the bridge rectifier and the switching FET. The primary filter can fail too but it's rare.
                        Last edited by Krankshaft; 07-23-2010, 10:46 PM.
                        Elements of the past and the future combining to make something not quite as good as either.

                        Comment

                          #13
                          Re: Fujitsu Siemens C383FA

                          Originally posted by seanc
                          Jamicon?

                          Jamicon don't make capacitors suitable for power supplies as far as I'm aware.
                          they do have Low ESR series (for example WL or MZ).. but i don't consider Jamicons in general to be reliable/long lasting..

                          Comment

                            #14
                            Re: Fujitsu Siemens C383FA

                            Originally posted by retiredcaps
                            Can someone do a sanity check to make sure company xyz cap type abc series zz works in a switch mode power supply for a computer LCD monitor?
                            Thanx for the hint, next time im definitely doing this
                            Originally posted by Krankshaft
                            Check the switching FET too usually the fuse blowing signifies a problem on the primary side the big semis that blow from surges are the bridge rectifier and the switching FET. The primary filter can fail too but it's rare.
                            Uhm, any tips on how do i actually do this ? as ive said before im kind of inexperienced in this matter ...
                            ... at the uni ive been doing just the basic stuff, working with coils, capacitors , resistors/thermistors and doing their measurements ... no transistors or any other components as of yet, so a few tips would be helpful.

                            Here are some close-up pics of PCB i took after taking out the rectifier and the big cap. These may help to identify components/problems.







                            It is kind of sunny here after raining for two days, so some photos might be sun-spoiled ...

                            Comment

                              #15
                              Re: Fujitsu Siemens C383FA

                              OK got the components yesterday, replaced the big fella, diode bridge and the fuse.

                              The unit powered on just fine, but when its in idle state the monitor makes a strange hissing noise if you hear very closely i.e put your ear to the base-stand where the PSU is located. When its heated up it wont do this. I have the other replacement caps but those, as mentioned before, are low quality Jamicon ones, some of them are even 85C rated ...

                              Should I do them anyways ?


                              HD: http://img.bagem.lv/images/236591497.jpg

                              Heres a pic of Live TV playing on it.

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