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    #1

    Multimeter LCD display blob

    Anyone know what this strange blob on the multimeter LCD display is? Ideas to repair it?

    Picked up the Beckman TECH 360 bench multimeter from fleabay in new condition. It's just been sitting in storage.
    I thought a polarizing film or heat, but the G segment looks dead on a digit.
    Attached Files
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    #2
    Re: Multimeter LCD display blob

    that can be caused by heat - it's in the glass.
    the digit is potentially another issue.
    have you stripped it yet to see how it's built?

    Comment

      #3
      Re: Multimeter LCD display blob

      It looks like this display has been subjected to uneven heat or something was up against part of the display

      Try putting the display in the sun and wait for the display to turn black and let cool down evenly and maybe it will be better if not then the display is ruined because of age I have seen this before but normal start on one of the edges and grows to the center of the display

      On the digit that not all the segments are there put a little pressure on the display where it is missing and see if appears if so the display is separating and no hope for it if it does not appear then something is wrong with the ic chip that controls the display

      Or the bounding wires that are incased in the glass have separated and the display is really going bad I have seen this as well or if the display is on a ribbon connector is not make a good connection or if it is in a ic socket holder it not making a good connection either

      I hope this helps you
      Last edited by sam_sam_sam; 06-06-2021, 06:20 AM.
      9 PC LCD Monitor
      6 LCD Flat Screen TV
      30 Desk Top Switching Power Supply
      10 Battery Charger Switching Power Supply for Power Tool
      6 18v Lithium Battery Power Boards for Tool Battery Packs
      1 XBox 360 Switching Power Supply and M Board
      25 Servo Drives 220/460 3 Phase
      6 De-soldering Station Switching Power Supply 1 Power Supply
      1 Dell Mother Board
      15 Computer Power Supply
      1 HP Printer Supply & Control Board * lighting finished it *


      These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

      1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
      2 Hem Saw Computer Stack Board

      All of these had CAPs POOF
      All of the mosfet that are taken out by bad caps

      Comment

        #4
        Re: Multimeter LCD display blob

        this is good for a project, led conversion.

        Comment

          #5
          Re: Multimeter LCD display blob

          Fixing this LCD multimeter by converting to LED seems like it would fall under thread https://www.badcaps.net/forum/showthread.php?t=63483 ...

          Comment

            #6
            Re: Multimeter LCD display blob

            well it's been done before - gearhead did a fluke 77 i think.

            Comment

              #7
              Re: Multimeter LCD display blob

              Lots of inspiration at

              http://mrmodemhead.com/blog/all-posts/
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              Comment

                #8
                Re: Multimeter LCD display blob

                I grabbed a spare Beckman LCD I have and unfortunately it shows the same LCD rot has started. Both displays are old, the one with a blotch is REVB 09/81, and the other is REVC 02/1982. It's not due to heat in use or storage.

                The problem seems to be the polarizer aging and going bad.
                The LCD display is a sandwich of two glass sheets, with reflective aluminum backing that likely has the polarizer on it? I haven't taken it apart.

                I've ordered a NOS 1991 part and will see how that does.

                Sorry but I love these old Gen. 1 Beckman multimeters, made in USA and just great-built for repairing gear. This bench Tech360 has a fast A/D, AC or AC+DC true RMS, 20 ohms scale, 4mA ohms source, which is good for testing parts, wire cables etc.
                I'd looked at Brymen but they are still cheap crap, problems with LCD contrast and a cheap rotary switch. Taiwan-build multimeters, not so great.

                The guy who got a custom replacement LED display for the old Fluke 8840, 8842 VFD looks nice.
                https://www.eevblog.com/forum/buysel...n-damaged-vfd/
                Some hassles because the VFD driver is 30V and the LED's are 3V though.
                Attached Files

                Comment

                  #9
                  Re: Multimeter LCD display blob

                  Perhaps the LED substitution would be a product idea after all, if there are so many of these meters out there with the bad display

                  Kind of surprised the IC can drive so much current, I mean, even the ICL 7107 had restrictions when running on LEDs that the 7106 did not because the 7107 would heat up while driving LEDs, affecting its accuracy.

                  Alas I already have two LED meters, both of which were designed with LEDs...

                  (Personally I think a backlit transflective LCD is best, so we can still use the DMM out in the sun...)
                  Last edited by eccerr0r; 06-06-2021, 06:14 PM.

                  Comment

                    #10
                    Re: Multimeter LCD display blob

                    I'm going to make an LED multimeter if I can source the HY3131 DMM IC. It seems to be locked down by NDA agreements or something. I have one Wavetek BDM-40 4-1/2 digit in the shop and it's so easy to read. It uses ICL7135 with driver transistors and IC. But I sorta killed it with a 10kV zap, it's not a tough multimeter lol.

                    Beckman Tech 350, 360 uses some strange custom Motorola zener diode for the protection clamp, not sure how it works at 1,500V
                    Tech 300, 310 use a gas tube.

                    Comment

                      #11
                      Re: Multimeter LCD display blob

                      I have an HP 4½ and a Viz/RCA 3½ which are LED based. I don't have batteries for either of these two meters so on AC power they stay.

                      Still having a tough time finding cal info for the Viz, so many pots in the meter...

                      Comment

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