Fluorescent desk lamp repair

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  • caphair
    Badcaps Legend
    • Nov 2011
    • 1249

    #1

    Fluorescent desk lamp repair

    Turned it on and heard a loud pop, opened it and a small 10uf 50v electrolytic capacitors had blown up.

    Is it safe to replace with a higher value like 47uf 100v? Or does it have to be exact value of old?
    Attached Files
  • kamel84
    New Member
    • Feb 2016
    • 9
    • islam

    #2
    Re: Fluorescent desk lamp repair

    thank you

    Comment

    • petehall347
      Badcaps Legend
      • Jan 2015
      • 4424
      • United Kingdom

      #3
      Re: Fluorescent desk lamp repair

      i would put a regular ballast in and starter if it doesn't already have one . less to go wrong

      Comment

      • petehall347
        Badcaps Legend
        • Jan 2015
        • 4424
        • United Kingdom

        #4
        Re: Fluorescent desk lamp repair

        just for fun here is an idea to use lamps that look worn out but arent . can be used on good lamps too .

        Comment

        • redwire
          Badcaps Legend
          • Dec 2010
          • 3900
          • Canada

          #5
          Re: Fluorescent desk lamp repair

          That capacitor is probably for limiting base-drive, so if it popped I think a transistor is shorted. Usually the lamp fails open circuit and then the PSU dies.

          These schematics are similar to your circuit but not exact - it's a two transistor resonant oscillator. The Philips/Osram one has no 10uF 50V cap.
          I don't see filament connections in that desklamp, only 2-wires leaving the PSU.
          Attached Files

          Comment

          • caphair
            Badcaps Legend
            • Nov 2011
            • 1249

            #6
            Re: Fluorescent desk lamp repair

            Originally posted by redwire
            That capacitor is probably for limiting base-drive, so if it popped I think a transistor is shorted. Usually the lamp fails open circuit and then the PSU dies.

            These schematics are similar to your circuit but not exact - it's a two transistor resonant oscillator. The Philips/Osram one has no 10uF 50V cap.
            I don't see filament connections in that desklamp, only 2-wires leaving the PSU.
            Thank you. So could I use a higher value capacitor or has to be exact?

            Comment

            • redwire
              Badcaps Legend
              • Dec 2010
              • 3900
              • Canada

              #7
              Re: Fluorescent desk lamp repair

              I say you can use a larger value OK. But it will pop... larger... If the transistors are bad.

              Comment

              • caphair
                Badcaps Legend
                • Nov 2011
                • 1249

                #8
                Re: Fluorescent desk lamp repair

                Originally posted by redwire
                I say you can use a larger value OK. But it will pop... larger... If the transistors are bad.
                Tried one nothing happened, no light as well. Does that mean transistors are ok since it didn't blow?

                Curious when is the exact capacitor value replacement necessary? What circuits can't be altered by higher capacitor values than original
                Last edited by caphair; 03-11-2017, 10:15 PM.

                Comment

                • eccerr0r
                  Solder Sloth
                  • Nov 2012
                  • 8678
                  • USA

                  #9
                  Re: Fluorescent desk lamp repair

                  petehall347, I'm sorry, I'm tired of those magnetic ballasts that flicker at 100/120 cycles/second... The electronic ballasts, though quite a bit more fragile, are smaller, lighter, more power efficient, and usually starts lighting faster.

                  caphair, likely you will have to carefully check each of the transistors for shorts, as well as making sure the input fuseable resistor didn't fry. Unfortunately all of the electronic ballasts I've had when they do go, tend to fry transistors and then input circuitry - a big domino effect.

                  Comment

                  • caphair
                    Badcaps Legend
                    • Nov 2011
                    • 1249

                    #10
                    Re: Fluorescent desk lamp repair

                    Originally posted by eccerr0r
                    petehall347, I'm sorry, I'm tired of those magnetic ballasts that flicker at 100/120 cycles/second... The electronic ballasts, though quite a bit more fragile, are smaller, lighter, more power efficient, and usually starts lighting faster.

                    caphair, likely you will have to carefully check each of the transistors for shorts, as well as making sure the input fuseable resistor didn't fry. Unfortunately all of the electronic ballasts I've had when they do go, tend to fry transistors and then input circuitry - a big domino effect.
                    Why are fuseable resistors used and not regular fuses?

                    Comment

                    • cpt.charlie
                      Badcaps Veteran
                      • Sep 2013
                      • 270
                      • Spain

                      #11
                      Re: Fluorescent desk lamp repair

                      Resistors are cheaper than proper fuses.

                      Comment

                      • petehall347
                        Badcaps Legend
                        • Jan 2015
                        • 4424
                        • United Kingdom

                        #12
                        Re: Fluorescent desk lamp repair

                        might not flash the same running off dc voltage . i have to try it soon so will let you know if it works out ok .
                        we are on 50hz here so its worse for me .
                        Last edited by petehall347; 03-12-2017, 05:25 PM.

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Fluorescent desk lamp repair

                          Why fusible resistor?
                          http://powerelectronics.com/passive-...t-applications

                          The flickering rate will be 100 Hz,
                          Electronic ballast uses much higher frequency.
                          Never stop learning
                          Basic LCD TV and Monitor troubleshooting guides.
                          http://www.badcaps.net/forum/showthr...956#post305956

                          Voltage Regulator (LDO) testing:
                          http://www.badcaps.net/forum/showthr...999#post300999

                          Inverter testing using old CFL:
                          http://www.badcaps.net/forum/showthr...er+testing+cfl

                          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                          http://s807.photobucket.com/user/budm/library/

                          TV Factory reset codes listing:
                          http://www.badcaps.net/forum/showthread.php?t=24809

                          Comment

                          • caphair
                            Badcaps Legend
                            • Nov 2011
                            • 1249

                            #14
                            Re: Fluorescent desk lamp repair

                            Revisiting this. Changed the cap and one of the transistors previously and it worked all this time.

                            Just recently quit again, this time no caps blew up and no shorts on the transistors or diodes or any of the caps (tested in ohms settings)

                            Any suggestions? I should just replace it but curious to get it going again

                            Comment

                            • eccerr0r
                              Solder Sloth
                              • Nov 2012
                              • 8678
                              • USA

                              #15
                              Re: Fluorescent desk lamp repair

                              did the tube go this time?

                              Comment

                              • caphair
                                Badcaps Legend
                                • Nov 2011
                                • 1249

                                #16
                                Re: Fluorescent desk lamp repair

                                Originally posted by eccerr0r
                                did the tube go this time?
                                Yes but even after replacing it's not working

                                Comment

                                • caphair
                                  Badcaps Legend
                                  • Nov 2011
                                  • 1249

                                  #17
                                  Re: Fluorescent desk lamp repair

                                  How many volts should I see at the lamp terminals when first powered on? I’m measuring 126v then drops to 86v

                                  Does that mean the circuitry is working and possible bad replacement lamp?

                                  Comment

                                  • eccerr0r
                                    Solder Sloth
                                    • Nov 2012
                                    • 8678
                                    • USA

                                    #18
                                    Re: Fluorescent desk lamp repair

                                    OCV it should be really high and then drop down fast when the light strikes. 126V seems a bit low depending on the length of the tube.

                                    Comment

                                    • caphair
                                      Badcaps Legend
                                      • Nov 2011
                                      • 1249

                                      #19
                                      Re: Fluorescent desk lamp repair

                                      What would cause it to be low? The tube is small and circular probably 12” give or take

                                      Comment

                                      • stj
                                        Great Sage 齊天大聖
                                        • Dec 2009
                                        • 30945
                                        • Albion

                                        #20
                                        Re: Fluorescent desk lamp repair

                                        strike voltage probably comes from an inductor or cap discharging

                                        Comment

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