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Thread: 3 volt AC from dc?????

  1. #1
    Constant Bitrate
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    Angry 3 volt AC from dc?????

    ok so i found an old pioneer tape deck with a VFD meter display on it. i took it apart looked at the board for it and it says it takes 3 VAC (i checked this with a volt meter) any one know how to get 3volts ac from dc? i would like to drop it into my case. thanks

    -Eric

    3 volts AC is for the logic.

    52 volts AC for the light

  2. #2
    Maximum Bitrate eugenen's Avatar
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    use the ckt from the deck? Follow the connections back from the display and trace out the ckt (hold the PCB up to a bright light to see through the traces on both sides) Unsolder the components or dremel the pcb. I've doen that before.

  3. #3
    FLAC
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    Originally posted by eugenen
    use the ckt from the deck? Follow the connections back from the display and trace out the ckt (hold the PCB up to a bright light to see through the traces on both sides) Unsolder the components or dremel the pcb. I've doen that before.
    What is the frequency?
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

  4. #4
    Maximum Bitrate eugenen's Avatar
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    I have never measured the frequency, just borrowed the circut. Sorry, if I find a working one laying around I will measure it. Wait I don't have an oscope anymore either.

  5. #5
    Constant Bitrate
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    Thumbs down

    no idea. i only have a multi-meter

  6. #6
    Low Bitrate
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    VFD 101

    The frequency will either be 50 or 60Hz depending if it is a European or US player. The 3V is used to heat up a wire filament at the front of the VFD and as such doesn't usually mind if it is fed AC or DC. It will heat up just as well with 3.3V DC. Current consumption should be around 50 to 200mA

    You mentioned a 52V AC which will more likely be reduced internally and used for the display logic. The heater filament has to be negative biased with respect to the phosphor layer (part that lights up) in order to produce any light. Typical bias is -24V

    VFD's work very similarly to a CRT TV screen and require a number of different voltages to operate. The VFD modules from the likes of futaba and noritake itron have all the voltage generation circuitry buit into them making them easy to work with.

    I learn't this the hard way trying to get a dvd player vfd to work on one of my power supplies. I fed it the 3.3V, -24V, 5V and 12V that it asked for but couldn't figure out why it wouldn't work. It wasn't untill I biased the 3.3V by the -24v that the display worked. It didn't matter if the 3.3V was AC or DC.

    Hmm I didn't mean to write so much.

    Sproggy

  7. #7
    Constant Bitrate
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    that was a very helpful post sproggy.

    i the 3 volts ac is between 2 posts.... 1 is blue and the other brown (i know you cant see it)

    from right to left the wire wrap posts are labeled as follows

    +B(52 volts) ac Rch GND Lch F F (underneath both Fs it says AC 3 v)

    i'm in the process of removing the power supply circuitry and putting in a case of its own (i'm thinking of getting a www.bottlehead.com foreplay tube pre-amp and integrating it into the case)

    after looking at the pcb i can see that the 3volts AC goes from one end of the display to the other (one on pin1 the other on pin 33, i take it i could put dc 3.3 to one and ground to the other?) (heating filement) but getting 52 volts ac would be tricky( it does go to the controller chips on it).

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