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Fixing a laboratory waterbath

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    Re: Fixing a laboratory waterbath

    I set it to a bit over 50 °C. It heated up and stopped the correct temp with no issues. What should I do at this point? I m tempted to ignore the abnormaly (if it is abnormal) low current. I don't know what to put in place of the blown resistance.

    One thing I noticed is the heatsink of the triac gets very hot. Too hot to touch, but suppose that's normal.

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      Re: Fixing a laboratory waterbath

      cant see the pic very good . are you sure its not saying 100 milliamps ?

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        Re: Fixing a laboratory waterbath

        Originally posted by petehall347 View Post
        cant see the pic very good . are you sure its not saying 100 milliamps ?
        The meter is on the 20m setting and shows 0.10 so that should be 0.10 mA if i m not mistaken.

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          Re: Fixing a laboratory waterbath

          The LM324 sitting on the 12/20V wire has a quiescent supply current of a milliamp by itself so you're seeing something less than 1mA (= 1000µA), the op amp is not getting power. This says nothing about all the other stuff on that line that also needs power.

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            Re: Fixing a laboratory waterbath

            more than a resistor blown then ..maybe the fuse in the meter or leads in wrong holes or something silly like that . or meter is on dc amps ..

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              Re: Fixing a laboratory waterbath

              Originally posted by eccerr0r View Post
              The LM324 sitting on the 12/20V wire has a quiescent supply current of a milliamp by itself so you're seeing something less than 1mA (= 1000µA), the op amp is not getting power. This says nothing about all the other stuff on that line that also needs power.
              Originally posted by petehall347 View Post
              more than a resistor blown then ..maybe the fuse in the meter or leads in wrong holes or something silly like that . or meter is on dc amps ..
              My apologies, it was in DC amps. I assumed AC or DC didn't matter since I was getting a reading. My multimeter also doesn't have AC amps. I borrowed one and measured again - the meter says about 75 mA.

              If this reading is correct, then going back to my previous calculations to drop 4v across a resistor, I would need 4/0.075 or about 53 Ohms. Should I try to see if there is something else fried or is 75 mA plausible?
              Last edited by vrasp; 06-20-2021, 07:05 PM.

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                Re: Fixing a laboratory waterbath

                I soldered a 50 ohm resistor. The voltage drop across the resistor is 2.9v. The current going through is therefore about 60 mA. I havent noticed anything wrong with the waterbath. It seems to be working fine.

                I will put everything back together tomorrow (carefully, unlike previous times), run it for a few hours, and see how it goes.

                Thanks a lot for your help guys!

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                  Re: Fixing a laboratory waterbath

                  Today I put everything back together. I used the cooling option to bring the temp down to 5 degrees Celsius then heated up the water to 80 degrees celcius. It ran for over an hour with no issues. I think it s ready to go back to the lab.

                  Now I ve been asked to look at a laboratory grade oven. Apparently it s also an electrical issue. I ll start a new thread if I need some help (which will likely be the case).

                  I ve already said this but I m really grateful for your help. I have very little experience fixing electronics so this was new to me. I learned a lot! Thank you for your patience and guidance.

                  Last edited by vrasp; 06-22-2021, 06:56 PM.

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                    Re: Fixing a laboratory waterbath

                    well done to all concerned .

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                      Re: Fixing a laboratory waterbath

                      Hey guys, I am back.. with an issue.

                      What happened:

                      The waterbath worked well for 2 days. I left it at 80 °C most of the day yesterday. As I was about to turn it off, I decided to press the cooling button. I had done that before without issues. This time, the display stopped working when I pressed it. When this button is activated, the cooling system (compressor amongst other things) is activated and creates some vibrations. No smoke or other relevant observations.

                      The details:

                      The waterbath still works. I can change the temperature. The water heats up. I can cool it using the cooling option. The LED on the display board works too (the yellow LED that indicates whether it is heating or reached chosen temperature).

                      What does not work is the display.

                      What I have done:

                      - I measured the current where I had put a 50-ohm resistor (before the bridge rectifier of the green/blue board). The last time, when it was working fine, I was getting around 75 mA. This time I m getting around 50 mA.
                      - I measured the voltages on the display board. It's getting 5-6v.
                      - I checked for a bad connection. I don't think there is any. Pocking stuff around did not make the display turn back on. There is continuity in all connections between the green/blue board and the display board.

                      I don't fully understand how the LM324DP and ICL7107SCPL work, but I think that LM324DP isn't related to the display. Since everything works fine except the display, I am tempted to say that it has to do with the ICL7107. Again, that's based on my basic understanding of the circuit.

                      Hopefully someone is able to give me a hint of what I can check with this information. How can I test ICL7107? What would you do at this point?

                      This is the most detailed schematic of the circuit (last page).

                      https://cdn.badcaps-static.com/pdfs/...78961c69cf.pdf



                      Thank you!
                      Attached Files
                      Last edited by vrasp; 06-24-2021, 10:14 PM.

                      Comment


                        Re: Fixing a laboratory waterbath

                        The ICL7107SCPL is nothing more that a voltage meter module you need to look at the data sheet for voltage in for the meter module to work and make sure you have voltage at these points that pins V+ which pin1 and V- pin26 ground pin is 21

                        Here is the data sheet website link

                        https://cdn.badcaps-static.com/pdfs/...7791fce5e7.pdf

                        You have to have a 5+ ground 5- for a power supply unless this unit has a negative power supply regulator ic chip

                        I hope this helps you
                        Last edited by sam_sam_sam; 06-25-2021, 09:14 PM.
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                        These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

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                        All of these had CAPs POOF
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                        Comment


                          Re: Fixing a laboratory waterbath

                          Originally posted by sam_sam_sam View Post
                          The ICL7107SCPL is nothing more that a voltage meter module you need to look at the data sheet for voltage in for the meter module to work and make sure you have voltage at these points that pins V+ which pin1 and V- pin26 ground pin is 21

                          Here is the data sheet website link

                          https://cdn.badcaps-static.com/pdfs/...7791fce5e7.pdf



                          You have to have a 5+ ground 5- for a power supply unless this unit has a negative power supply regulator ic chip

                          I hope this helps you
                          Thank you. I did check pin 1 earlier today and it had 0v. Injecting 5v turned on the display. I checked what the v+ is connected to and found a component that had 6v on its first pin but 0v on the other pin going to the ICL chip.

                          This is the component. It says 825 then A below it.

                          I think something is shorted to ground somewhere on this line.
                          Attached Files

                          Comment


                            Re: Fixing a laboratory waterbath

                            If you inject 5V and it turns on, and it's not drawing a lot of power, this line doesn't sound shorted, it sounds open, and isn't that connector a previous point of weakness?

                            Comment


                              Re: Fixing a laboratory waterbath

                              component looks like a 6.2v zener 500mw

                              Comment


                                Re: Fixing a laboratory waterbath

                                I think the line has continuity though. I have to double check.

                                I injected 5v by using one if the LED power lines and connecting it directly to v+ of ICL. The display turns on, its dim, but it turns on. I dont know how much power it draws. I guess I could put my ammeter in there too.

                                My assumption was that the component I showed in the previous picture was broken. I put a wire instead to see what would happen but still 0v. However when nothing is connected, one pin has 6v. Wouldnt that mean that something is shirrer to ground?

                                I was going to check the other components on this line. This is the line.

                                The black lines mean there is a component on the other side.
                                Attached Files
                                Last edited by vrasp; 06-26-2021, 05:02 AM.

                                Comment


                                  Re: Fixing a laboratory waterbath

                                  never just bridge components if you don't know what they are .
                                  that zener is there for good reason . and most likely should read 6.2v right across it .

                                  Comment


                                    Re: Fixing a laboratory waterbath

                                    Originally posted by petehall347 View Post
                                    never just bridge components if you don't know what they are .
                                    that zener is there for good reason . and most likely should read 6.2v right across it .
                                    My bad. I first thought it was a tiny resistance and thought it wouldnt cause any issues.

                                    Yes, it read 6.2v on one pin but not on its pin going to the display. Do you think the zener is the issue?

                                    Comment


                                      Re: Fixing a laboratory waterbath

                                      My next step is to double check for continuity and if there is continuity, check each component on this line to make sure it s doing its job.

                                      Comment


                                        Re: Fixing a laboratory waterbath

                                        zener appears fine ,
                                        bridging resistors can also make bad things happen .. in fact bridging anything can ..just don't do it . test the suspects properly .

                                        Comment


                                          Re: Fixing a laboratory waterbath

                                          There is continuity from the output of the zener all the way to the v+ of ICL. The input of the zener has 6.2v and 0v on the output
                                          Last edited by vrasp; 06-26-2021, 08:05 AM.

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