Suggestion to identify (and find) a replacement CCFL transformer

Discussion in 'Power Electronics' started by foxOnTheRun, Jul 29, 2018.

  1. foxOnTheRun

    Thread Starter New Member

    Jun 8, 2010
    9
    0
    As the title says, my scanner's ccfl tube/driver is dead. The original light, with the same board out of the scanner, powered with a 12v source produces no light.

    I wanted to find a replacement for the onboard transformer, I thought a quick search would yeld some replacemet part.. but nope! They are really hard to find (?). Its layout is the one pictured below:
    coiltronics 210607 schematic.jpg

    Between pin 6 and 10 I measure 196ohm, the feeback has around 0,6ohm, the primary between 1 and 3 it's 1,5ohm and the middle reads around 0,7/0,8 between 1 and 3. It looks fine.. never the less I simply wanted to replace all the parts, tube too, keeping the original board.

    Where do I start looking for a trafo replacement? I only found some promising parts on https://www.coilcraft.com/ccfl.cfm, and given the input voltage, I'll need a 2,5W N=100, but the form factor is wrong: I need a through-hole pinout.

    I also disassembled a standard CCFL inverter for modders, but the circuit is slightly different and the transformer has another pinout. I would have simply replaced the board, but the one in the scanner has a compact shape with a hole in the middle for a screw :(

    Funny detail, if I hover my hand over the tube/board it lights up more (better if I also hold something metallic - but never more than half). Also, I identifyed the scanner's board as a simple Royer circut, exaclty the one (type 1, the simplest) you can find on the wikipedia page.

    CCFL_Inverter_Circuit1.gif

    I replaced all the parts, one by one with no improvement what so ever, apart the transformer. So in the end: is it the trafo or still something else? Tnx!
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,586
    1,250
    Forget the transformer , you won't find one, best option is to use an inverter from a 12V fluorescent light, or use an inverter from a working cfl lamp, as these are four wire types.
     
  3. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,205
    1,117
    Probably a dud lead - but I'd ask the Spanish HR company, they were famous for excellent quality TV flyback transformers. They got into TV backlight CCFL driver boards, but they may have withered since LEDs started taking over.
     
  4. foxOnTheRun

    Thread Starter New Member

    Jun 8, 2010
    9
    0
    Is there any way I could find out? In conductivity mode the multimeter gives solid result. The board "looks" quite fine, all the components were swapped and the transformer has the "right" resistances values.

    The board is somehow different in that the transformer is on the opposite side of the Cold Cathode connection witht he high voltage leads running on the outside perimeter up to the small cap and to the connector.

    I'll solder some jumpwires and see how it does.
     
  5. foxOnTheRun

    Thread Starter New Member

    Jun 8, 2010
    9
    0
    So I connected directly on the secondary of the transformer the cap and a piece of wire to the Cathode.. and it turned on! albeit very dim. At first 2/3 already, then hovering my hand over it, it lit up completely, but nowhere its original brightness.

    I quickly swapped the tube to another inverter laying nearby and when lit it's really bright (so, tube is 100% fine on another inverter).

    So it must be the leads.. somewhere.. nice! I'll scrape all the insulating mask behind and run a new layer of this all over as a test, if it works I'll replicate the circuit on another board shaping it the best I can.
     
  6. foxOnTheRun

    Thread Starter New Member

    Jun 8, 2010
    9
    0
    I rebuilt the circuit on a new breadboard, guess what.. it doesn't work at all o_O

    Looking at the circuit above, transistor Q2 starts to become very hot; well, not that I let it to thermally run away, I can quite feel the characteristic "hot air" smell, so I unpower the circuit immediately (less than a second).

    Wondering why it won't start to oscillate. I measured the hfe of both npns and is a solid 160. I'm 99.999% the wiring is right, visually I can follow the connections. Side note, the npn is a 2SC2383 with a "ECB" pinout and I can confirm the bases being connected to the feedback coil and the emitters directly to ground (also the transformer pinout/functions are easy to keep in sight).

    :(:(:(
     
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