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    eBay Chinese Electronic Clock Kit

    Ok so I bought one of these kits from eBay, which eventually arrived:

    https://www.ebay.co.uk/itm/DIY-Green...72.m2749.l2648

    Now I soldered everything how I thought was a-ok with my knockoff of a Hakko 936D iron.

    However when powering nothing happened at all. Even using a 3V coin cell nothing also happened.

    I tried rotating the switch (see centre right) and the cap in the images blew its guts out.

    The polarity seems ok as I think that the solid line on the PSU (little 9V 100ma switcher) is the negative which would go to ground?

    How do I know which way round the switch goes?

    Am I a dummy?
    Attached Files

    #2
    Re: eBay Chinese Electronic Clock Kit

    did you test polarity of power supply ?

    Comment


      #3
      Re: eBay Chinese Electronic Clock Kit

      Originally posted by petehall347 View Post
      did you test polarity of power supply ?
      Ok - another stupid question - the black lead is going V(Omega cymbol)mA and the red is going to COM - let me guess... this is the wrong way around??

      Btw I have no formal background in electronics!!

      Comment


        #4
        Re: eBay Chinese Electronic Clock Kit

        if you have a multimeter test the power supply voltage just incase its been wired up wrong inside the adapter part. Can you post a picture of the back of the clock pcb so we can look at the traces etc.
        Last edited by vinceroger69; 10-06-2018, 02:42 PM.

        Comment


          #5
          Re: eBay Chinese Electronic Clock Kit

          cap is correct way round and is rated at 25v .
          the switch is easy to work out with your multi-meter .
          mostly capacitors blow up from reverse voltage or too high voltage .
          Last edited by petehall347; 10-06-2018, 03:06 PM.

          Comment


            #6
            Re: eBay Chinese Electronic Clock Kit

            This is how my multimeter is wired... the black connector (negative) I am putting against the wire with the white strip down it on the PSU... it reads 8.88V which seems about right.
            Attached Files

            Comment


              #7
              Re: eBay Chinese Electronic Clock Kit

              Originally posted by Rulycat View Post
              Ok - another stupid question - the black lead is going V(Omega cymbol)mA and the red is going to COM - let me guess... this is the wrong way around??

              Btw I have no formal background in electronics!!
              if this is your multi-meter black goes to com . red to VΩ
              if wiring is backwards meter will read in negative .. example -9
              Last edited by petehall347; 10-06-2018, 03:13 PM.

              Comment


                #8
                Re: eBay Chinese Electronic Clock Kit

                Originally posted by petehall347 View Post
                if this is your multi-meter black goes to com . red to VΩ
                if wiring is backwards meter will read in negative .. example -9
                Looks like I am reading the PSU backwards then... which means white line is +VE!!! That will be why cap has blown!!

                D'oh!!!

                Comment


                  #9
                  Re: eBay Chinese Electronic Clock Kit

                  the transistor next to it might be blown too plus other things .

                  Comment


                    #10
                    Re: eBay Chinese Electronic Clock Kit

                    For the cost of it I should just order another and chalk it up to stupidity.

                    Comment


                      #11
                      Re: eBay Chinese Electronic Clock Kit

                      try a new cap and see how it is then . best to get quality ones anyway .

                      Comment


                        #12
                        Re: eBay Chinese Electronic Clock Kit

                        Got some crap caps at my dads house so for the sake of £2 lets see if anything else is goosed and if not then I'll put proper caps on it.

                        Comment


                          #13
                          Re: eBay Chinese Electronic Clock Kit

                          Originally posted by petehall347 View Post
                          the transistor next to it might be blown too plus other things .
                          Underneath the cap is a 5V 78L05 regulator. They generally withstand reverse voltage on them for a while. It might be worth trying the circuit without the exploded capacitor, it should work given 8V.


                          http://hipcatcoolcap.blogspot.com/20...879-clock.html

                          Comment


                            #14
                            Re: eBay Chinese Electronic Clock Kit

                            £3 - inc post.
                            still an amazing price for 3 displays, a microcontroller that costs more than that at RS probably, and a pcb!!

                            Comment


                              #15
                              Re: eBay Chinese Electronic Clock Kit

                              Originally posted by Harvey View Post
                              Underneath the cap is a 5V 78L05 regulator. They generally withstand reverse voltage on them for a while. It might be worth trying the circuit without the exploded capacitor, it should work given 8V.


                              http://hipcatcoolcap.blogspot.com/20...879-clock.html
                              i did wonder where the regulator was .i did guess it had something to do with it but never thought it was the actual regulator .
                              if dc is smooth i agree it shouldn't need the cap to test it . old 9v block battery might be a better choice as supply

                              Comment


                                #16
                                Re: eBay Chinese Electronic Clock Kit

                                Actually, having looked at the circuit diagram, the clock should work just off the 3V battery...

                                Comment


                                  #17
                                  Re: eBay Chinese Electronic Clock Kit

                                  i assumed 3v was a backup supply . will check schematic now .

                                  Comment


                                    #18
                                    Re: eBay Chinese Electronic Clock Kit

                                    it is a soldering project .. am wondering if anyone has a working one ...

                                    Comment


                                      #19
                                      Re: eBay Chinese Electronic Clock Kit

                                      Originally posted by petehall347 View Post
                                      i assumed 3v was a backup supply . will check schematic now .
                                      I assumed that too, but its to be connected through a diode to the vcc supply... unless the MCU has voltage sensing and goes into backup (no display) mode below a certain voltage.

                                      I also notice there is a resistor bypassing this diode (I can't make out the numbers on the circuit diagram) that CHARGES the 3V battery when connected to a supply! So DON'T use a standard 3V coin cell in there or you'll have another exploding component!.



                                      *EDIT * What goes on with R12 on your PCB? Trick of the light or has that only got one band?
                                      Attached Files
                                      Last edited by Harvey; 10-06-2018, 04:45 PM.

                                      Comment


                                        #20
                                        Re: eBay Chinese Electronic Clock Kit

                                        gah, I do wish people would scan circuit diagrams in with enough clarity that its possible to read them. I'm wrong, it DOES need more than the 3V supply, there's 2 VCC rails, one for the MCU, one for the LEDs.
                                        Last edited by Harvey; 10-06-2018, 04:52 PM.

                                        Comment

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