Sansui LCT32SD not switching on

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  • Grunder
    Badcaps Veteran
    • Jan 2016
    • 323
    • south africa
    #1

    Sansui LCT32SD not switching on

    Hi guys,

    I need help determining the value of two components on the power supply.
    I've included a photo of the pcb with the components high lighted.

    IC6 = L6599 Hv resonant controller Turquoise square. Vcc is pin 12 (self limiting).
    IC3 = opto couple Yellow square.
    Trans 5. 2SA1815 (on top of pcb) marked Green. measured okay.
    Trans 6. 2SA1015 (on top of pcb) marked Blue. Short/ replaced.
    Diode 9. (on top of pcb) marked yellow. okay.
    R30. determine value. marked Red. burned beyond recognition.
    Zener diode determine value. marked Red. short No inscription.

    I tried a 1 ohm (feed resistor?) in position R30. and 5v8 for the Zener.
    But set wouldnt switch on and both slowly got hot and burned black.

    I tried electro tanya for the diagram, but no luck.

    I'm hoping one of the guys on BADCAPS with design knowledge, might be able to determine the values. Thanks.

    I forgot to say the 5v stby is there, and the psu-on does appear when pressing standby button, with led going from red to green. I reckon IC 6 isn't getting a supply, so it cant drive the transformer responsible for generating the 9,12 & 24v rails
    Attached Files
    Tags: None
    • Grunder
      Badcaps Veteran
      • Jan 2016
      • 323
      • south africa
      #2
      Re: Sansui LCT32SD not switching on

      Anybody?

        Comment

        • Grunder
          Badcaps Veteran
          • Jan 2016
          • 323
          • south africa
          #3
          Re: Sansui LCT32SD not switching on

          Hi Guys,

          Took a chance and done a little experimentation.

          Replaced the burned resistor with a 120 ohm 1/4 watt resistor (photo 1)
          Replaced the shorted zener with a 12v zener.

          Set now switches on (backlights on), and working perfectly! (Photo 2)

          I guess the resistor was a limiting resistor, and the first attempt using the 1 ohm allowed too much current through, burning up the zener.

          I now get 12v across the zener in standby. 11.3v when the set is running.
          I now get 10.7 volts supplied to pin 12 (Vcc) on the Hv resonant ic.
          Attached Files
          Last edited by Grunder; 01-19-2017, 08:32 AM. Reason: typo

            Comment

            • dick_barton
              Badcaps Legend
              • Aug 2015
              • 6642
              • Wales
              #4
              Re: Sansui LCT32SD not switching on

              What was IC7's part number?
              Willing to help but I'm no expert.

                Comment

                • Grunder
                  Badcaps Veteran
                  • Jan 2016
                  • 323
                  • south africa
                  #5
                  Re: Sansui LCT32SD not switching on

                  Hi Dick,

                  You might not have seen my recent post (3 min before your reply).
                  I did manage to get the set running.
                  I didn't identify IC 7, I also suspected IC 7 got damaged. Set has been closed up.
                  Thanks response.
                  Last edited by Grunder; 01-19-2017, 08:28 AM. Reason: typo

                    Comment

                    • dick_barton
                      Badcaps Legend
                      • Aug 2015
                      • 6642
                      • Wales
                      #6
                      Re: Sansui LCT32SD not switching on

                      Hi, I did see your post but was thinking that the data sheet for IC7 would give typical component values to check against what you used.
                      Willing to help but I'm no expert.

                        Comment

                        • Grunder
                          Badcaps Veteran
                          • Jan 2016
                          • 323
                          • south africa
                          #7
                          Re: Sansui LCT32SD not switching on

                          Hi Dick, quite right, checking the specs on that ic(7) would have given me a better idea of what voltages to expect in that area.

                          She's running now with no heat or burning of the components fitted, if she comes back (hope not), I will investigate further.

                          Thanks for the input.
                          Last edited by Grunder; 01-19-2017, 09:05 AM.

                            Comment

                            • dick_barton
                              Badcaps Legend
                              • Aug 2015
                              • 6642
                              • Wales
                              #8
                              Re: Sansui LCT32SD not switching on

                              Willing to help but I'm no expert.

                                Comment

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