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.

https://i.ibb.co/KyqQwXH/20210620-115441.jpg

Re: Fixing a laboratory waterbath
 

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

Re: Fixing a laboratory waterbath
 

The meter is on the 20m setting and shows 0.10 so that should be 0.10 mA if i m not mistaken.

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.

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 ..

Re: Fixing a laboratory waterbath
 

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?

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!

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.

https://i.ibb.co/dr5WzqF/20210622-203511.jpg

Re: Fixing a laboratory waterbath
 

well done to all concerned .

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).

http://www.hvg-verwertung.de/ebay/do...da/RMS6_20.pdf



Thank you!

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://media.digikey.com/pdf/Data%2...007,%2007S.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

Re: Fixing a laboratory waterbath
 

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.

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?

Re: Fixing a laboratory waterbath
 

component looks like a 6.2v zener 500mw

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.

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 .

Re: Fixing a laboratory waterbath
 

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?

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.

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 .

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