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Hitachi SuperScan Pro 800 - No Picture, No B+

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    Hitachi SuperScan Pro 800 - No Picture, No B+

    Moved from this topic to improve exposure to members.

    Hitachi SuperScan Pro 800
    20" Color Monitor
    Max resolution: 1600x1200, 60-75Hz
    Model: CM800U

    According to ex-owner, monitor had a picture shrinkage problem that had gone on for some time. It made a click sound and would pull in from the sides. I know the sound well because I have the identical monitor. It is a relay, and in mine I get the click sound and the same result, reduced horizontal sweep. It seems a tap on the case clears the problem so I'm certain it's a cold joint or loose connector somewhere. Okay, back to the victim...

    While using the monitor one day, it suddenly went *pop* and went dark. Power indicator lamp stayed steady on. Cycle the power and it makes the degauss noise, but remains dark.

    Okay, I inherit monitor and get it on the bench. Let me say this is a beast and it is a technicians nightmare. Five (5) shield panels must be removed to get to the chassis. There is a large 11" x 14" panel that holds a microprocessor board standing vertically and plugged into the mainboard at the rear. While connected, the only chance for access to the components is over the horizontal output section, straight down from the top or from the underside of the mainboard. The mainboard is completely outlined in a plastic guard/insulator that comes up past the edge of the board and extends into the solder side a full inch. There is no access to this area of the board without removal of this "guard". There is no moving the unit on the bench without assistance, as you have exposed components at the edge once the guard is removed. So here it sits, on its side.

    Diagnosis continues in next post...
    veritas odium parit

    #2
    Re: Hitachi SuperScan Pro 800 - No Picture, No B+

    Diagnosis so far -

    - NOTHING accounts for the *pop* sound. No burnt smell, no burned, cracked, split, bulged parts, no arc marks, no scorching. It all looks like a brand new unit, sans dirt and expected discoloration for a 12 year old unit.
    - the click sound is a relay near the yoke connection that jumpers an inductor on the board. Same sound mine makes and makes sense that it's something to do with the width control for different resolutions.
    - no B+
    - no High voltage
    - B+ rises to 20-25 volts then shuts down and stays down until power cycle
    - High voltage pulses to 2-3kv then off, follows B+
    - unit has B+ switcher supply, a second separate switcher supply for all other main voltages, and a 5v standby circuit.
    - other voltages from second supply seem normal -12, 6.3, 12, 25, 80
    - Usual suspects (HOT) and surrounding power transistors all seem to test okay. Nothing shows shorted.
    - traced B+ into horizontal section, lifting component legs as I went and watching B+ rise to nominal 50-60 volt level. I reconnect the component and move on.
    - Horizontal sweep signal present at Base of HOT and at Emitter, but no amplification due to no voltage.
    - Pulling the horizontal yoke connector produces about -125v at HOT Emitter and B+ rises to 45v.
    - Inductance and Ring test on H yoke section seems fine. 86.5µH and 10-14 count on Sencore Z-Meter LC-53.


    HELP!
    veritas odium parit

    Comment


      #3
      Scoped Horizontal area readings

      1 - Base of HOT
      2 - Emitter of HOT
      3 - H-OUT pin of FBT
      Attached Files
      veritas odium parit

      Comment


        #4
        Re: Hitachi SuperScan Pro 800 - No Picture, No B+

        sounds like the flyback to me..
        arcing over, causing the noise and the "image shrinking", till the arcing finally destroyed it.

        just a guess though..

        Comment


          #5
          Re: Hitachi SuperScan Pro 800 - No Picture, No B+

          Originally posted by Toasty



          While using the monitor one day, it suddenly went *pop* and went dark. .
          Encountered the same problem with an Acer 76e CRT.
          But the screen would come back when I turned the power off then back on.
          Last edited by RJARRRPCGP; 03-05-2009, 05:25 PM.
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            #6
            Re: Hitachi SuperScan Pro 800 - No Picture, No B+

            @RJARRRPCGP-
            I wish that were the case here. At least I could get some readings with it working to track the failure.

            @Scenic-
            If it's the FBT, I'm afraid it will be a "spare parts for mine" unit. The only one I finding is from Meitone in China. BW00562 B

            However, I am confused as to the indications and readings I'm getting. I think it's kicking in the EHV limiter circuit. If that's an indication of the FBT being bad...
            veritas odium parit

            Comment


              #7
              Re: Hitachi SuperScan Pro 800 - No Picture, No B+

              https://cdn.badcaps-static.com/pdfs/...96564c4d75.pdf

              Keep in mind, your monitor will have 2 horizontal circuits, one for the horizontal yoke, one for HV. Use your scope probe's body, lay it against the flyback's core, you will get train of thin parabolas along mostly straight trace. This is how I can see if fly is working or not, same with the other transformer for the yoke. Do this same trick.

              You have lost the other feed for the yoke circuit. This happens when transistor shorted out, also find FET and resistors, they will be also bad. Find it.

              The waveforms on the emitter of the horizontal transistor, I don't like it!
              Is this emitter connected at ground potiential? Remember which horizontal transistor, for HV or for horozintal circuit?

              The loud snap and pic narrowing then gone is HV blowing things out.

              Cheers, Wizard
              Last edited by Wizard; 03-05-2009, 07:36 PM.

              Comment


                #8
                Re: Hitachi SuperScan Pro 800 - No Picture, No B+

                The Emitter scope trace is incorrectly labeled and noted above. That is the Collector trace. The Emitter is grounded.

                That transistor's Collector is connected directly to one side of the yoke.

                All transistors were again verified by ohmmeter as not shorted. FET's do not show shorted either. All 1 watt or better resistors check okay. Fusible resistors check okay. Two(2) large, high-voltage (1.6kV & 2.2kV) caps pulled and tested okay - no leakage and on capacitance spec.

                The pics were difficult to get while holding the camera and powering on the unit. They only last 1/2 second because B+ circuit shuts down.

                - Probe against FBT
                - H-OUT pin of FBT, 5µs
                - H-OUT pin of FBT, 10µs

                { Edit: Seems the forum doesn't present pics in the order they're uploaded. I will label pics directly from now on }
                Attached Files
                Last edited by Toasty; 03-06-2009, 03:07 AM. Reason: Pictures not in sequence presented
                veritas odium parit

                Comment


                  #9
                  Re: Hitachi SuperScan Pro 800 - No Picture, No B+

                  Fly is blown or bad parts in the circuit somewhere (after the fly judging by this traces).

                  Lot of noise in the trace. I'll show you what a good fly looks like some time which I happen to have a 3 CRT tv on bench replacing 2 CRTs (2.14H frequency but the design is exactly similar to monitor in most areas.)

                  Active pincushion, dynamic focus, blah blah.

                  Cheers, Wizard
                  Last edited by Wizard; 03-06-2009, 10:16 AM.

                  Comment


                    #10
                    Re: Hitachi SuperScan Pro 800 - No Picture, No B+

                    exactly similar ???
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                    Comment


                      #11
                      Wizard's response, updated info

                      Thank you Wizard. I was afraid of that. Most interested to see traces. Yeah, they're in some of my old books, but live pics are better.

                      More confirmation from previous owner. Screen was not just pulling in from sides as it was originally described as doing. It was an overall shrinkage, similar to having a 17" picture on this 20" screen. That was accompanied by a tic-tic-tic-pop sound, and then the pic would go back to normal. It had gone on for several days and then finally died.

                      The symptoms now sound exactly like what Scenic said a ways back.

                      I sent an email to Meitone to see if they can send me one at a reasonable price. I don't expect to hear from them until Monday, as it's already Saturday there.


                      >>exactly similar ???<<
                      Zactly. Like sorta-kinda-almost. Geeze...
                      veritas odium parit

                      Comment


                        #12
                        Re: Hitachi SuperScan Pro 800 - No Picture, No B+

                        Similar yes. What I'm referring is CONCEPT.

                        The basic circuit of deflection stuff is same, more circuits are added on to this deflection circuit. There are deflection-only circuit using a transformer *without* HV windings. Which you do have as well but behaves same on waveforms.

                        Here's the traces of a 2.14H (HD):



                        This following picture is +76V DC output monitored on the anode of this diode.



                        Cheers, Wizard

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