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    Vacuum Fluorescent Display issue

    Hi All,

    Dear old Ma's ancient Toshiba microwave oven (model ER-7700) has an intermittent problem with the display, which is of the VFD variety. The display works fine - sometimes, but fades out or completely disappears during use. Tapping on the display usually brings it back, but only temporarily until it drops out again. I've had it apart several times looking for the obvious bad connection / solder etc. but no joy. Hoping someone on here can suggest a likely failure mode for this type of display and how best to go about troubleshooting it. I attached a short video clip to show the problem. Thanks.
    Attached Files

    #2
    Re: Vacuum Fluorescent Display issue

    resolder the first few pins at each end - or just all the pins.
    and post pictures of the board

    Comment


      #3
      Re: Vacuum Fluorescent Display issue

      Yes it looks like a bad connection on the display's filament circuit.
      The giveaway is the slow fade out when it cuts out.

      I would resolder the display's pins (filament pins are at the tube's outside ends) and I follow those board traces back to the small power transformer and resolder at that end as well.

      Comment


        #4
        Re: Vacuum Fluorescent Display issue

        Thanks for the replies. Re-soldering all the pins seems to have helped in that the display will now stay on for longer (30 - 40 mins ?) but eventually it still goes out. As can be seen in the pic there was some blackening around pin 1 which I didn't notice the last time I took it apart - but this was maybe 4 or 5 months ago and it has been steadily worsening since then, so maybe it wasn't as obvious back then. Anyway, still scratching my head as to where to look next.
        Attached Files

        Comment


          #5
          Re: Vacuum Fluorescent Display issue

          The bad connections may be at the source of the filament voltage, follow the two traces from the vfd and you will likely find the problem.
          Attached Files
          Last edited by R_J; 06-02-2023, 09:17 AM.

          Comment


            #6
            Re: Vacuum Fluorescent Display issue

            Apologies for the lengthy delay in updating this but have been out of the country for a couple of months. Also thanks for the replies so far. Sad to say I haven't been able to resolve the problem. Re-soldered the filament connections at both ends of the board, and used the solder-sucker to clean them out and then re-soldered again. After this attempt (today) the display stayed on constantly for over 10 hours. Thumping, banging, tapping, and knocking on it - no problem, it stayed lit. Put the cover back on it and brought it inside, then after several more hours, suddenly and without provocation, it went off. I'm afraid I'm out of ideas and ready to admit defeat. Such a shame as I hate to throw out such a classic piece of kitchen retro. If anyone can suggest anything else I can try I'm happy to have another go at it, otherwise it's time for a replacement. Thanks again.

            Comment


              #7
              Re: Vacuum Fluorescent Display issue

              your so close.
              does the heater go through an electrolytic capacitor?

              Comment


                #8
                Re: Vacuum Fluorescent Display issue

                Well i think i finally found the problem. Re-soldered the main molex connector (circled) that brings power to the boards from the mini-transformer, and fingers crossed the display has been fine for 2 days of normal use now. The solders on the connector looked fine but I guess maybe a hairline crack somewhere? Anyway, thanks again to all for the suggestions and encouragement.
                Attached Files

                Comment


                  #9
                  Re: Vacuum Fluorescent Display issue

                  Hopefully that's it. I just resolder the entire path for the filaments, end to end because some fractured joints are too hard to see.

                  How do the two boards connect to one another? That is another place to check.

                  Comment


                    #10
                    Re: Vacuum Fluorescent Display issue

                    Originally posted by redwire View Post
                    Hopefully that's it. I just resolder the entire path for the filaments, end to end because some fractured joints are too hard to see.



                    How do the two boards connect to one another? That is another place to check.
                    The 2 yellow ribbon cables (pic 1461) are soldered directly to each board. If it plays up again I'll go over these.

                    Comment


                      #11
                      Re: Vacuum Fluorescent Display issue

                      I once worked in a repair shop and it was very bad to have something brought back in, not fixed right. So I go after the problem- find the bad connection and then fix it so the Boss does not whomp my ass
                      The other techs who would guess and not fix it for sure had a lot of re-calls lol. It was one payoff for me, to troubleshoot deeper, it just worked out better at work.
                      For a home appliance though, you don't need to but what a hassle taking it apart again. The big range-top microwave ovens I hate taking down to fix. Last time I was covered in cooking grease and oil and the thing weighs like 40lbs.
                      It was because the exhaust fan chute can be set to go up into a duct to the roof, or vent out the front if you have no roof vent. The condo install crew had it vent out front even though there was a duct... everything was covered in cooking oil.
                      I know yours is a big table top microwave, probably just as heavy.

                      Comment


                        #12
                        Re: Vacuum Fluorescent Display issue

                        Originally posted by redwire View Post
                        I know yours is a big table top microwave, probably just as heavy.
                        Spot on.....as the saying goes "they don't make 'em like that any more". I'd say 40lbs is about right. Must have carried it out to the garage 5 or 6 times - it was a grunt !

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