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vacuum fluorescent display (VFD) help

Discussion in 'Troubleshooting and Repair' started by looxuser, Mar 10, 2016.

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  1. looxuser


    Dec 28, 2015
    I am in the process of repairing my old hifi when I came across another one cheap at a local boot fair.

    It seems to have exactly the same display in the tuner section yet the one I recently got has a much dimmer display than my original. See image (dimmer one top)


    When metering out the supplies to the displays each seems to have about the same voltage going to each on the display outer power supply pins. There was an article here Mine however don't seem to have any components in series to consider as suggested in this thread but suppose thats irrelevant if the correct voltage is present?

    I wonder if the brightness of the poorer one can be improved, but would appreciate some insights into how these VFD things work and the significance of the voltages please?
  2. shrtrnd


    Jan 15, 2010
    First off, thoroughly check your manual, and see if you have some kind of 'dimmer' option activated that's unintentionally dimming the display.
    Second, these old Flourescent Vacuum Displays where hot stuff when they came out because they were the newest fancy thing.
    I don't know anybody that makes them anymore.
    A characteristic of the display is that it dims with age, unavoidably.
    I've had to trash many perfectly functional instruments when the display became so dim you just couldn't read it anymore and nobody made a replacement display anymore.
    Good luck. I hope you've just got some dimmer function activated, otherwise this is something you're just going to have to live with.
  3. looxuser


    Dec 28, 2015
    Thanks I have heard of cooking the filaments with higher voltage which seems to rejuvenate them?
  4. looxuser


    Dec 28, 2015
    So I've learnt something today from Youtube about VFD's...They have a filament power supply, a grid supply and supplies to the anodes. What people seem to indicate is about 3-5volts through the filaments. I'm getting -22.4 volts DC at either end of the display terminals, so no volt drop / potential difference showing, or so tiny my DVM not picking that up on its scale. Anyone got any thoughts on what i should be seeing here? What aspect of the VFD design influences brightness is the the filament voltage. Another source said that if the grid is too negatively biased that would result in dim display but i'd welcome views on that too. Cheers, Andy
  5. GPG


    Sep 18, 2015
    AC . measure between the pins
  6. 73's de Edd

    73's de Edd

    Aug 21, 2015

    Sir looxuser . . .

    . . .
    STRANGE . . .but your first query on your other AIWA thread was relevant to some parts used in a VFD display of your old AIWA.
    Of course that was in no way, related to your current problem you are having on that unit.
    That PROBABLY accounts for the stored schematic of a similar AIWA that I have, and was initially using for reference against yours, until we noticed the different parts numbering assignments.
    I believe that VFD display section has identical circuitry and parts numbering.
    Sooooo . . . . . you now have yourself another tuner, but with dim display, That was the same problem on the other AIWA and it got analyzed and repaired, but he stopped short of further checking out ALL of the portions that I wanted to more fully verify. He was happy enough with a display probably working at 80-90% max brightness.
    Lets finish the current Function switching analysis and repair, and then I will guide you thru that other units display restoration.
    BTW give me the full AIWA model number of the new tuner . . . .only . . . . . X-D9 is now visible . . . .of a probable MX-D9 ?.

    73's de Edd

    Last edited: Mar 11, 2016
  7. looxuser


    Dec 28, 2015
    HI GPG, thanks for your comment, yes so have checked across the pins on AC with DVM and on the good display I get 2.2v and on the poorer one 3.3v. Reading around the internet on this it also seem to relate to the tuner on all these old systems and I wondered whether this was because they displayed the clock 24-7 whilst on standby and it just aged the VFD.

    I did wonder what element of a VFD to vary to vary brightness, surely the anode voltage. Saw a youtube video where this was happening but it was in German.

    Hi 73's de Edd, yes you are correct early in our current diagnosis of the switching issue I was initially just probing round the test points on my board and recall the point was marked VFIL -31v and i got a much lower value. Think its was a problem with my DVM at the time. Display is ok.

    Have updated status on the switching repair by the way. Thanks for your ongoing support.
    Last edited: Mar 11, 2016
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