Fixing a laboratory waterbath

[sam_sam_sam]

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

[vrasp]

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!

[petehall347]

Re: Fixing a laboratory waterbath

well done to all concerned .

[vrasp]

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.

[vrasp]

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!

[vrasp]

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.

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?

[petehall347]

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 ..

[eccerr0r]

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.

[vrasp]

Re: Fixing a laboratory waterbath

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.

[petehall347]

Re: Fixing a laboratory waterbath

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

[vrasp]

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.

[vrasp]

Re: Fixing a laboratory waterbath

I ve tried a few things. The highest current I m getting is 0.x milliAmps, so in the hundreds of microAmps.

I hardwired the manual temperature switch and I m able to adjust the temperature setting. The water temperature goes up as it should. It looks like everything is working as it should.

[vrasp]

Re: Fixing a laboratory waterbath

No, I'd expect the proper 'on' current for the 12 and 20V lines to be measured in milliamps, if it's measured in microamps, something is wrong.

Maybe it s not on. Let me see if pushing a button changes anything

[vrasp]

Re: Fixing a laboratory waterbath

I want to add that when I turn on the waterbath without connecting those wires together, the display displays 0s, and when I connect the wires, it shows the water temperature (which is correct). If I hardwire the switch (i just pinched the center and outer metal with tweezers) the temperature goes up. It seems like everything is working as it should. This current is confusing.

[eccerr0r]

Re: Fixing a laboratory waterbath

No, I'd expect the proper 'on' current for the 12 and 20V lines to be measured in milliamps, if it's measured in microamps, something is wrong.

[vrasp]

Re: Fixing a laboratory waterbath

Hey guys,

The triac has been replaced with a NTE5671 800VRM 20 amps.

I measured the amperage by connecting my multimeter where the resistor used to be and I am getting about 10 microAmps. Is this possible? In the picture I had removed the lightbulb but it was there as a precaution the first time I measured the current.

If it really is 10 microAmps, then based on the voltage formula V=R*I, if I want to drop the voltage by 4v (18v from the transformer to 14v to reduce load on the bridge rectifier), then:

4 = R * 0.000010
R = 400K

Seems a bit much...Am I doing this right?

[vrasp]

Re: Fixing a laboratory waterbath

Thanks guys! I was going to try your suggestions. However, another bad news. I spent the day yesterday moving to my new appartment. While bring the waterbath to the new place, one of the pins on the Triac broke. This waterbath is very heavy, over 100 pounds easy. The pins of the triac must have been bent somehow and broke off. This is a picture of it. You can still see the pin and I have tried to put solder on it so I can hook up a wire but the solder is not staying on.



I did some reading about triacs. I m not sure what it s used for. Apparently it's used to switch the heating control? The good news is that I know it's a IT715 which is 800VRM and 15amps TO-220. Can I buy another 800v 15amps or are these other specs to look at?

Since I m not sure of the importance of the triac, I want to ask: Can I bypass it while I conduct the test with the lightbulb to figure out the resistance of the blown resistor? Or Do I have to install a new triac first?

This is quite frustrating. I really tried to be careful during transport.

[petehall347]

Re: Fixing a laboratory waterbath

Sounds like a use for another lightbulb!

good plan .

[eccerr0r]

Re: Fixing a laboratory waterbath

Sounds like a use for another lightbulb!

[petehall347]

Re: Fixing a laboratory waterbath

all it has to do is protect the rectifier and be capable of passing enough current for the circuits to work properly with a bit of overhead . without a schematic i am a bit lost .. i would take a chance and sub in an ammeter with say a 300ma fuse and briefly power it up and see what sort of current is being used . this like anything has its risks . some things just like to take whatever current is available .led.s for example .no idea about the display and if it has its own protection resistors or not .
i have done things like this by taking a guess at the resistor value and trying it to see how hot it gets . trouble is not knowing if there is now a problem that might burn the correct value resistor .