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Dimmer

Discussion in 'Troubleshooting and Repair' started by partyanimallighting, Oct 22, 2012.

  1. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Hi. Can anyone help me? I have a small dimming circuit board in need of repair. It's for a Furman Rack Mount Power Supply and the dimmer ciscuit is for the rack lights built into the unit. What I believe is a triac is burnt out on the circuit board and the number is ST44A. I have searched for a replacement and cannot find this number listed. Can anyone advise?
     
  2. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Pictures?
     
  3. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012

    Here is a picture.
     

    Attached Files:

  4. duke37

    duke37

    5,231
    718
    Jan 9, 2011
    It looks like a normal 5A or so triac. There are many triacs which could do the job such as BT06-6008, 600V 8A.

    The question is, why did it fail. Did you mistreat the output?
    I would replace the capacitor in case this is faulty and change the diac (very cheap) also.
    Check the twiddle pot for resistance.

    You could probably get a standard light dimmer as cheap as the parts.
     
  5. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Hi Duke,

    It's a really small circuit board, probably only an inch long, and the wires shorted when I tried to replace one of the 2 7W 120V bulbs and that blew out the triac. The triac number was ST44A and I could not find a listing for it to get a replacement number and ST44A is not available locally. The other parts, the diac (MBS4991 429) and two capacitors (2A154J. and .082+/-10% 10IGG), seem to be fine and also a small resistor so I think I just need to change the triac but I need a suitable replacement number. My knowledge of electronics is pretty basic, I can source problems to some extent, but a full understanding of how things work and how to troubleshoot them, that has me stumped so that's when I turn to the experts, you guys!!
     
  6. duke37

    duke37

    5,231
    718
    Jan 9, 2011
    It is good to know what caused the trouble.
    I picked a device from an old Maplin catalogue, there are many others. The only thing to watch for is to get a device in a TO220 case. You do not want a surface mount type.
    As far as I know the connections are the same on all devices.
     
  7. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Hi Duke37,

    So I shouldn't be too worried about getting a replacement? A lot of the dimming equipment I stock for stage lighting rentals carry a common device, LM7805. I have a few of these lying around. Will this device work? And if not, what would you recommend?
     
  8. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    No the LM7805 is a 5 volt regulator, you need a triac for this application, same package but totally different part...

    As for recommendations as Duke suggested, it appears from the number you provided that the original is a 4A triac... So any of these will suffice to get you started, using a higher Amp one might prevent premature failure in the future...

    BTA04-600 (4 Amp)
    BTA06-600 (6 Amp)
    BTA08-600 (8 Amp)
    BTA12-600 (12 Amp)

    Should all suit your needs, just make sure they are in the TO220 package so they fit right in...
     
  9. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Thanks Cocacola,

    I'll pick up a couple tomorrow and try my luck.
     
  10. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    When I solve this problem I have another circuit board in need of repairs also. Can I bother you guys with this one when that time comes?
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,191
    2,693
    Jan 21, 2010
    Sure!
     
  12. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Thanks guys,

    I picked up a NTE substitute for the BTA04-600 for about USD6.00 locally and it worked fine. The dimming is not as smooth as before but it will suffice. Thanks again for all the help and advice and I'll post pictures of my next problem pcb over the course of this weekend. Any help will be appreciated.

    Once again, thanks for all the assistance.

    partyanimallighting
     
  13. JMW

    JMW

    90
    3
    Jan 30, 2012
    Nah!! the first one is free, after that we need tickets, lots and lots of tickets
     
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