(Topic ID: 227783)

Vacuum Fluorescent Display


By BlueSea

7 months ago



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  • 21 posts
  • 7 Pinsiders participating
  • Latest reply 7 months ago by BlueSea
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    IMG_4435.JPG
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    3.8 ohm.PNG
    oven 1 (resized).jpg
    Oven display.jpg

    #1 7 months ago

    I have exhausted my resources on general electronics forums, and am taking a guess that pinball machines at some point used Vacuum Fluorescent Display or VFD. From the looks of this display (bright in middle, dim on top and bottom), is this a recognizable problem that can be fixed? The consensus I received on general electronic forums is that the display is worn out and cannot be fixed. I already changed all the caps and tested all the diodes. My goal is to return the display to full brightness. Thanks for any thoughts.

    Oven display.jpg
    #2 7 months ago

    Hopefully it does not need re-gasing

    #3 7 months ago

    On pinball displays, you can "recharge" them by running 9v through the filaments for 5-10 seconds to burn off the build-up & corrosion on the filaments.

    #4 7 months ago

    Did anyone else except Gottlieb use VFDs?

    I was taught that they couldn't be recharged, but.. I'd be curious to know for sure now.

    #5 7 months ago
    Quoted from Coyote:

    Did anyone else except Gottlieb use VFDs?

    Wico did on Af-Tor. I'd venture to guess they were used by some other oddball manufacturers as well.

    #6 7 months ago

    There was a Bally prototype for an early solid state design that used vfd displays.

    I'm pretty sure Gottlieb was the only one that used vfd displays extensively. They sure made the right decision to not go with plasma displays, IMHO.

    #7 7 months ago
    Quoted from ForceFlow:

    They sure made the right decision to not go with plasma displays, IMHO.

    For sure. I also really love the way they stand out in a gameroom. The rich blue/green on all their games definitely stands out.

    I just hate the fact that the A/N displays are essentially unobtainium. Especially the lesser used larger font units used in System 3. Good thing they last forever.

    #8 7 months ago

    Like anything else - I would start by ruling out more fixable items such as the power supply. Low voltage on the supply? Simply replacing caps and diodes doesn't mean a fully functioning supply.

    #9 7 months ago
    Quoted from mbaumle:

    For sure. I also really love the way they stand out in a gameroom. The rich blue/green on all their games definitely stands out.

    I was mainly referring to their longevity.

    Quoted from mbaumle:

    I just hate the fact that the A/N displays are essentially unobtainium. Especially the lesser used larger font units used in System 3. Good thing they last forever.

    I got some NOS glass and blank PCBs at some point, so theoretically, I could make my own. However, now that I think about it, I don't exactly recall what sizes/models the glass and PCBs we're, so I'm not sure if they'll match up. Hmmm

    #10 7 months ago
    Quoted from russdx:

    Hopefully it does not need re-gasing

    Thanks, I believe it is a vacuum so there should not be gas in the tube. The tube has a getter located in the upper left hand corner of the display (picture attached) which is still black. The getter is supposed to turn white if there is a leak.

    Wiki "A getter is a deposit of reactive material that is placed inside a vacuum system, for the purpose of completing and maintaining the vacuum. When gas molecules strike the getter material, they combine with it chemically or by absorption. Thus the getter removes small amounts of gas from the evacuated space." https://en.wikipedia.org/wiki/Getter

    oven 1 (resized).jpg
    #11 7 months ago
    Quoted from ForceFlow:

    On pinball displays, you can "recharge" them by running 9v through the filaments for 5-10 seconds to burn off the build-up & corrosion on the filaments.

    Thanks, the display is not uniformly dim, rather it is brighter in certain spots. Is that a characteristic sign of build-up and corrosion on the filaments?

    Also, 9v sounds like I should use a 9v battery. Should I run wires straight from the battery to the cathode pins? Or do I need to limit the current from the 9v battery? Thanks.

    #12 7 months ago
    Quoted from G-P-E:

    Like anything else - I would start by ruling out more fixable items such as the power supply. Low voltage on the supply? Simply replacing caps and diodes doesn't mean a fully functioning supply.

    Thanks. What would you suggest testing? Sounds like I need to measure the current going into the cathode and anode pins while the unit is connected to AC power. That seems like the only way to know for sure if the transformer and rectifier are passing along the correct DC voltages. I know the unit is getting AC power as other functions are working, like the spark module which uses 120v AC. The display is from a gas oven.

    #13 7 months ago

    Hard to say without seeing schematics on that specific version.

    There is usually a filament voltage in addition to cathode and anode voltages. Without any form of schematics, tough to say if any are missing. But based on photo in first post - I would check the filament voltage. Now what that voltage is and where to find it is particular to the specific display on that board -- impossible to define without schematics or further information.

    #14 7 months ago

    Who's your friend? Google is your friend. I Googled: "recharging gottlieb displays" and got instructions, Youtube videos and everything else you need to do this safely.

    Give it a shot, you don't have anything to lose.

    Don C.

    #15 7 months ago
    Quoted from Don_C:

    Who's your friend? Google is your friend. I Googled: "recharging gottlieb displays" and got instructions, Youtube videos and everything else you need to do this safely.
    Give it a shot, you don't have anything to lose.
    Don C.

    Keep in mind, this is *not* a VFD that Gottlieb used. This is something else, which may (and likely does) have a completely different pinout on the glass. Connecting voltage to the wrong pins may (and probably will) cause damage.

    #16 7 months ago

    Guess he'll have to cook in the dark!

    Don C.

    #17 7 months ago

    Thanks for the Gottlieb reference. I previously tried a 9v battery but when the filaments turned red after 1 second I got concerned and pulled the battery. The Gottlieb video (the one by Todd's Tips) addresses the amp question. Rather than use a 9v battery, he suggests using a wall adaptor that is 9v and 500 to 700 ma, cutting off the end of the adaptor and replacing with alligator clips, and applying power to the horizontal filaments for 10 seconds. The outside pins on the Gottlieb are the same on my unit - they are for the horizontal filaments (i.e., the cathode). I have an extra 9v adaptor and I am going to follow the steps in Todd's video. Link to Todd's video below. Thanks, I will let you know if it works.

    #18 7 months ago
    Quoted from BlueSea:

    I previously tried a 9v battery but when the filaments turned red after 1 second I got concerned and pulled the battery.

    That's normal.

    And to be clear, the filaments are the horizontal wires in the display (there should be about 5 of them, depending on the size of the display). If the digits are turning red, then that's bad.

    #19 7 months ago

    Well, that did not go well. Magic smoke. I don't have a schematic for my unit, and it apparently has a different design than the Gottlieb. Anyway, I tried the recharge process using an old 9v 600ma adapter. Cut the ends off, added alligator clips. My mistake was not watching closely, instead I was fumbling with my phone to take a picture. I first saw the smoke in the screen of my phone as I was taking a picture. I got a good picture of the glowing red filaments and the smoke:

    IMG_4426.JPG

    I quickly unhooked the alligator clip and investigated. There is a resistor tied into the VFD filaments. It looks like it is coming from the supply side. Maybe it is to limit the current flowing to the filaments. The resistor smoked pretty bad, and smelled bad, to the point it was very difficult to read the rating of the resistor.

    IMG_4428.JPG

    I tested the resistor and it read about 3.9 or 4 ohms, and luckily the side of the resistor facing the board was still barely readable, and the 4 band markings tend to indicate 3.9 ohms (orange gray gold gold).

    IMG_4435.JPG

    3.8 ohm.PNG

    It looks like 3.9 ohms is a common size and luckily the resistor still appears to work (although I should order a new one and replace it). Some of the coating wore off but it looks like all metal underneath which would be appropriate for a 3.9 ohm resistor (as a much higher resistor would have a coiled wire look underneath the cover):

    IMG_4430.JPG

    I cant figure out Ohm's Law in this case. If the resister is 3.9 ohms, and the likely voltage feeding the filaments is 4 or 5 volts (typical for a VFD), then that resistor in normal operation is passing about 1 amp of current. It looks like a 1/4 watt rated resistor, which does not make sense because if it is passing 1 amp of current, it is passing about 5 watts. Anyway, since the resistor still appeared to be working, and since I did not have a spare on hand, I reassembled the unit and it appears to be working in the oven with no change in appearance in the display. If the resistor shorted, the filaments would be glowing red and eventually burn out but they are not. I think I will leave good enough alone at this point and live with a dim display.

    Thanks for any thoughts. Some pictures attached.

    #20 7 months ago
    Quoted from BlueSea:

    My mistake was not watching closely

    You should have only had them connected for less than 10 seconds.

    #21 7 months ago

    The smoke started after about 2 or 3 seconds. It never got to 10 seconds.

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