Fixing a laboratory waterbath

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  • petehall347
    Badcaps Legend
    • Jan 2015
    • 4422
    • United Kingdom

    #101
    Re: Fixing a laboratory waterbath

    no idea how much free space is in the connector pass throughs on the board but maybe pinning through with single strands of wire might help .

    Comment

    • vrasp
      Senior Member
      • Nov 2019
      • 194
      • Canada

      #102
      Re: Fixing a laboratory waterbath

      Originally posted by petehall347
      no idea how much free space is in the connector pass throughs on the board but maybe pinning through with single strands of wire might help .
      I dont have anything that small. It looks like the inside has metal "tweezers" that hold the pin when inside and I dont want to deform them.

      I m letting the board sit in 99% isopropanol overnight. Hopefully it s gonna dislodge whatever is in there. I suspect somebody in the lab spilled some sticky solution in there. I was also able to melt some solder where the holes are to make them smaller. The pins dont get in rhat easily but at least there is contact.

      Now why did the car lamp start flickering when the LED board was on I dont know. Something grounded? The LED board barely has anything on it. I guess it might make it easier to solve.

      Comment

      • sam_sam_sam
        Badcaps Legend
        • Jul 2011
        • 6018
        • USA

        #103
        Re: Fixing a laboratory waterbath

        The pin connection on the right hand side of the green looks like crap it appears to be flux from the picture if so re-solder them or is it just the way the picture was taken

        Comment

        • vrasp
          Senior Member
          • Nov 2019
          • 194
          • Canada

          #104
          Re: Fixing a laboratory waterbath

          Originally posted by sam_sam_sam
          The pin connection on the right hand side of the green looks like crap it appears to be flux from the picture if so re-solder them or is it just the way the picture was taken
          It s not the way the picture looks. It was actually quite bad. Cleaned it off but havent reappplied solder yet.

          Is the car lamp blinking for sure caused by a short to ground in the LED board if it only happens when it is connected?

          Comment

          • eccerr0r
            Solder Sloth
            • Nov 2012
            • 8658
            • USA

            #105
            Re: Fixing a laboratory waterbath

            If that car lamp glows very brightly, interpret it as if you just had to stick in another fuse.

            Comment

            • vrasp
              Senior Member
              • Nov 2019
              • 194
              • Canada

              #106
              Re: Fixing a laboratory waterbath

              Originally posted by eccerr0r
              If that car lamp glows very brightly, interpret it as if you just had to stick in another fuse.
              It s not very bright. You can just see the filament warm up. And now that I think about it, it could just be blinking because of the constantly changing number on the LED which varies the power drawn.

              Could it just be normal that the car light lights up slightly? I dont wanna look for an issue where there is none.

              Comment

              • eccerr0r
                Solder Sloth
                • Nov 2012
                • 8658
                • USA

                #107
                Re: Fixing a laboratory waterbath

                Yes it's fine for it to be dim. Don't worry about it, it's expected.

                The sole alert is if that it glows brightly - it saved you from replacing another fuse.

                Comment

                • vrasp
                  Senior Member
                  • Nov 2019
                  • 194
                  • Canada

                  #108
                  Re: Fixing a laboratory waterbath

                  While I try to figure out how to properly fix the connections between boards, can someone explain to me how the knob system works? In this case, the knob serves to pick a preset temperature.

                  Is the plastic knob supposed to have a circuit that touches the the metal parts of opposite sides to activate the circuit? I m just guessing here. I need to understand how it works to see hownit can be fixed.

                  The actual knob (not shown in this picture) goes into the white round thing on the top board of this picture.

                  Comment

                  • eccerr0r
                    Solder Sloth
                    • Nov 2012
                    • 8658
                    • USA

                    #109
                    Re: Fixing a laboratory waterbath

                    That's about it, just selects different resistors...

                    Comment

                    • vrasp
                      Senior Member
                      • Nov 2019
                      • 194
                      • Canada

                      #110
                      Re: Fixing a laboratory waterbath

                      Originally posted by eccerr0r
                      That's about it, just selects different resistors...
                      Thank you. I was asking because the knob I have does not have any metal in it. I think I might have broken it while trying to remove it from the board and maybe the metal part got lost.

                      I think I m going to buy a new rotary switch. The one on the board works by creating a contact between the center golden circle and the outer golden metal. I d like to get a similar one. Is there a specific name for this?

                      If you have other suggestions to replace this switch let me know! Thank you

                      Comment

                      • eccerr0r
                        Solder Sloth
                        • Nov 2012
                        • 8658
                        • USA

                        #111
                        Re: Fixing a laboratory waterbath

                        if you're inclined to look for the small metal piece lost, it probably looks like a bent leaf.

                        The unfortunate thing is that getting an exact match will be hard...mainly to fit in the board. Rotary select switch is pretty much is all you can look for, and it appears to be a 5 throw 2 pole (DP5T) rotary (of which it really just needs 1 pole but the original designer appears to have cheesed the switch to make it easier to route PCB tracks?) perhaps if you can't find the leaf it's easier to just hardwire it to the adjustable setting?

                        Comment

                        • vrasp
                          Senior Member
                          • Nov 2019
                          • 194
                          • Canada

                          #112
                          Re: Fixing a laboratory waterbath

                          Originally posted by eccerr0r
                          if you're inclined to look for the small metal piece lost, it probably looks like a bent leaf.

                          The unfortunate thing is that getting an exact match will be hard...mainly to fit in the board. Rotary select switch is pretty much is all you can look for, and it appears to be a 5 throw 2 pole (DP5T) rotary (of which it really just needs 1 pole but the original designer appears to have cheesed the switch to make it easier to route PCB tracks?) perhaps if you can't find the leaf it's easier to just hardwire it to the adjustable setting?
                          I didnt think of that! That would save me the trouble of looking for a proper rotary switch. I m gonna see if I can do that right now.
                          Last edited by vrasp; 06-17-2021, 02:41 PM.

                          Comment

                          • vrasp
                            Senior Member
                            • Nov 2019
                            • 194
                            • Canada

                            #113
                            Re: Fixing a laboratory waterbath

                            Originally posted by eccerr0r
                            if you're inclined to look for the small metal piece lost, it probably looks like a bent leaf.

                            The unfortunate thing is that getting an exact match will be hard...mainly to fit in the board. Rotary select switch is pretty much is all you can look for, and it appears to be a 5 throw 2 pole (DP5T) rotary (of which it really just needs 1 pole but the original designer appears to have cheesed the switch to make it easier to route PCB tracks?) perhaps if you can't find the leaf it's easier to just hardwire it to the adjustable setting?
                            How do I hardwire it? I thought I just had to wire the fifth outer pin (that corresponds to the manual temperature selection) to the inner pin (golden metal ring). Things started getting smoky and I turned it off immediately. The smoke came from one of the capacitors or the resistance next to it. I think I reacted quickly enough. If I have to replace it it's no big deal. However, I don't understand what pins to wire.

                            Basically, I did this:
                            Last edited by vrasp; 06-17-2021, 02:41 PM.

                            Comment

                            • vrasp
                              Senior Member
                              • Nov 2019
                              • 194
                              • Canada

                              #114
                              Re: Fixing a laboratory waterbath

                              The capacitor is fine. It is the resistance that blew.



                              Are you able to see the lines? I can't tell what ohm this is.

                              Comment

                              • petehall347
                                Badcaps Legend
                                • Jan 2015
                                • 4422
                                • United Kingdom

                                #115
                                Re: Fixing a laboratory waterbath

                                go through your pictures to find a good close up of the resistor .

                                Comment

                                • vrasp
                                  Senior Member
                                  • Nov 2019
                                  • 194
                                  • Canada

                                  #116
                                  Re: Fixing a laboratory waterbath

                                  Originally posted by petehall347
                                  go through your pictures to find a good close up of the resistor .
                                  I did, it s really difficult to see.

                                  The bands look like Red brown something (grey?) brown red. Of course the blown resistor had to be the one that is the least visible in the pictures.

                                  Is there a trick to figure out the resistance of a blwon resistor before it blew?

                                  Comment

                                  • petehall347
                                    Badcaps Legend
                                    • Jan 2015
                                    • 4422
                                    • United Kingdom

                                    #117
                                    Re: Fixing a laboratory waterbath

                                    tell us what it connects to ?

                                    Comment

                                    • eccerr0r
                                      Solder Sloth
                                      • Nov 2012
                                      • 8658
                                      • USA

                                      #118
                                      Re: Fixing a laboratory waterbath

                                      appears to be a kind of jumper... which could explain the need for 20V as there'll be a drop across this resistor to reduce heating of the regulator...

                                      Comment

                                      • vrasp
                                        Senior Member
                                        • Nov 2019
                                        • 194
                                        • Canada

                                        #119
                                        Re: Fixing a laboratory waterbath

                                        Originally posted by petehall347
                                        tell us what it connects to ?
                                        It's getting 20v AC from the transformer and on the output it goes to the bridge rectifier which goes to the voltage regulator.


                                        Originally posted by eccerr0r
                                        appears to be a kind of jumper... which could explain the need for 20V as there'll be a drop across this resistor to reduce heating of the regulator...
                                        The voltage regulator is a 7812. If I am able to find out more or less how much current is in this circuit I can calculate the resistance needed to lower the voltage from the 18v of my toroidal transformer to about 13-15v. Is that a good approach? I could connect my multimeter in series to measure the current where the resistor was, and calculate a resistance that would drop the voltage by, let's say, 5v.

                                        Comment

                                        • eccerr0r
                                          Solder Sloth
                                          • Nov 2012
                                          • 8658
                                          • USA

                                          #120
                                          Re: Fixing a laboratory waterbath

                                          The resistor may still be good. Measure it.
                                          I don't understand why it smoked, sure you didn't short something else by mistake?

                                          Comment

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