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Power Suppy Transformer viz / rca WP-703A

Discussion in 'Troubleshooting and Repair' started by rmdrmd, Jun 14, 2013.

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  1. rmdrmd

    rmdrmd

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    0
    Jun 14, 2013
    The transformer in my constant voltage power supply has melted.
    it is a VIZ model WP-703A (same as RCA WP-703A).
    the numbers on the top of the transformer are:
    9603-014
    and
    EIA 831 8619.
    Because it has failed I cannot test the output voltage - I need the output voltage so that I can replace the transformer with a similar one. Cant seem to find any info for this part number on the web.
    Anyone know a method for determining transformer output specs ? (without counting all the windings manually)
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Tell us more about the power supply.

    What is the output voltage (or range of output voltages) and the maximum current?

    How many wires are connected to the transformer (i.e. coming out of the transformer)
     
  3. rmdrmd

    rmdrmd

    13
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    Jun 14, 2013
    It plugs into 120 volts AC. 50 - 60 hertz.
    The unit supplies from 0 to 20 volts DC. Very precisely regulated.
    Max load is 500 milliamps.
    There are two wires into the transformer (mains supply), and three wires out (to the circuit board). There are no markings on the circuit board indicating the voltage coming from the transformer.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Hmmm, I was hoping you'd say 4 wires.

    Can you post some pictures.

    And why did it "melt"?
     
  5. rmdrmd

    rmdrmd

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    Jun 14, 2013
    ok.
    so here are some photos.
    as to why did it melt ? look, I think it was probably due to a crappy (poorly regulated) input voltage. see the last image. that is a 240v to 120v converter (electronic) I have been running it through this electronic voltage regulator successfully for nearly two years - but usually for only a few minutes at a time. immediately prior to this failure I had been running it for around 24 hours continuous. (then the smoke came out).
    ideally I will now replace the transformer with one that I can connect directly to Australian mains power - nominally 230v 50 Hz.
     

    Attached Files:

  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, your best bet is to get a 240V transformer to replace it and do away with the voltage converter.

    I would suggest that the transformer is probably around 36V center tapped, but we'd need to see the other side of the PCB. The transformer would need to be rated for 750mA or more.

    (great photos so far by the way)

    You're going to have to pull this thing apart and clean it.

    What country are you from? ...because someone is selling one here.
     
  7. rmdrmd

    rmdrmd

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    Jun 14, 2013
    So here are images of both sides of the board.
    Currently living in Australia. Not looking to buy another one running at 110V. Best for me is just to fix this one with a 240V transformer.
     

    Attached Files:

  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Do all the red wires have that yellow stripe? Or is it unique in the leads which connect to the transformer? And cant you match the leads now you've cut them?

    The secondary may be OK. Can you use a multimeter to read the resistance between all combinations of pairs of the secondary leads?

    I'd like to confirm where the centre tap went.

    If I have time later today or tomorrow I'll draw up a circuit.

    Can you also weigh the transformer.

    Thanks
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Also, can you read the part number from the small transistor.
     
  10. rmdrmd

    rmdrmd

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    Jun 14, 2013
    The three transformer wires are different - I have marked them in the diagram.
    The secondary winding does seem intact. (good thinking)
    Red/yellow to Red = 3.0 Ohms.
    Red/black to Red = 3.1 Ohms.
    Red/yellow to Red/black = 0.3 Ohms.

    The transformer weighs just a touch over 500 grams ( 1lb 2oz ).

    I have marked two small transistors on the board A and B.
    A is marked 8515 2N5183.
    B is marked K8444 2N3904.
     

    Attached Files:

  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I haven't forgotten you!

    Hmmm.... Those resistance measurements are odd...

    It sounds to me like red and red/black are the ends of the winding and that red/yellow is the tap. It also sounds like the red/yellow to red/black winding is shorted (and this would be the reason the transformer has melted like it has) .

    Thanks for the names of the transistors.
     
  12. Pioneer621

    Pioneer621

    13
    0
    Aug 3, 2010
    Hello, I have one of those VIZ WP-703A supplies, use it only occasionally, but it works. Figured I would measure the transformer voltage.

    With no load (other then the regulator circuitry) the voltage I get is:

    29.4v – 0 – 29.4v AC

    So 58.8vAC across the windings, & 29.4vAC referenced to the center tap. The wire with yellow on it is the center tap.

    Don’t know if this helps any, just seen the thread & thought I’d post since I have one of them things myself.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That is of a great deal of help!

    Thanks

    The voltage on the capacitors suggest the secondary voltage is this high, but I would really not have expected it to be.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I'm searching for transformers that would be a suitable replacement that you should also be able to find easily:

    here is one: http://www.altronics.com.au/index.asp?area=item&id=M4925A (the mounting will be difficult and the voltage is a little low). you also might want to go for the higher rated version if you regularly use the power supply at or near the max current: http://www.altronics.com.au/index.asp?area=item&id=M5025

    Here is something from RS, but it's PCB mount and a lower voltage again. http://australia.rs-online.com/web/p/pcb-transformers/2017606/
     
  15. rmdrmd

    rmdrmd

    13
    0
    Jun 14, 2013
    thanks people for all that assistance.
    I will hunt down an appropriate transformer and get this thing up and running again.
    very happy to have found this excellent forum.
    thanks again.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The transformers I have suggested are not ideal.

    Perhaps you could try to find 28-0-28...
     
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