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What methods do you use to test LM239 comparators?

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Postal2:
I encountered difficulties when testing LM239 comparators in a circuit. Not only do leaks appear at the inputs, which disrupt the external voltage divider and, as a result, change the response thresholds, but also cross leaks occur between 4 comparators, which are extremely difficult to discover.
At the moment, I use the method of complete replacement of all comparators. With this approach, I get one out of 6 comparators that is faulty.
Accordingly, I want to have (buy) a device that tests these comparators. First of all, I want to know the name of such a device, if anyone uses something similar.

Swake:
I assume that your use case it the classic one that compares two analog signals and outputs a digital signal, or something very similar. In such a case you might want to inject some signal from an external source directly on the input pins to verify if the output acts as expected.

If you encounter this frequently in the same context/equipment: thoroughly document the behavior of the circuit, make and write down many measurements and compare good vs bad case. You might want to use older HP style service manuals as example. btw, if it really happens frequently you should suspect an issue with the design. Comparators fail like any other component, but certainly not often.

Unless the fault is obvious like a short between pins or a burnt hole in the case, the only good method I'm aware off to verify if an op-amp or comparator is still working is to measure it out of circuit.

We might need more context to give you a better answer. What is the comparator used for? How many devices do you have to repare and what is the value of these? -> The investment in additional equipment might not be justified. In certain cases: just swap the component as it is quicker and cheaper.

Postal2:

--- Quote from: Swake on January 05, 2025, 11:32:01 am ---... In such a case you might want to inject some signal from an external source directly on the input pins to verify if the output acts as expected. ...

--- End quote ---
This does not work in case of the defects described above. While input leakage can somehow be dealt with in this way, I was unable to deal with cross leakage.

--- Quote from: Swake on January 05, 2025, 11:32:01 am ---...We might need more context to give you a better answer. What is the comparator used for? How many devices do you have to repare and what is the value of these? ....

--- End quote ---
ZAPI (photo). There are already more than one a year with such a defect. Basically, such defects are associated with marginal people trying to fix them.

Poroit:
G'day Postal2,

I have only ever used a digital multimeter for testing these.

I was fortunate and had a known working PCB so was able to measure and record all the Input and Output voltages and then compare them to other faulty PCB's.

Purchased replacements from Element 14.

Postal2:

--- Quote from: Poroit on January 06, 2025, 05:18:30 am ---...I was fortunate ...

--- End quote ---
That's what I'm saying, it's a lottery. That's right, you've found a leak at the input. But in rare cases (I had one like that), there are no leaks that cause voltage changes. And each comparator reacts separately to pull-ups and pull-downs. Replacing them all solves the problem. I came to the conclusion that this is due to cross-leaks, I may be wrong, but each element was checked carefully separately.
That's right, a reliable store solves the problem and replacing several pieces is not difficult, although this is done blindly.
The problem is that good original LM239s run out and those come that have a defect of 1 out of 10. Thus, when carrying out a mass replacement, I encounter a defect in new chips, and everything starts from the beginning.
And if checking logic chips or operational amplifiers is not difficult, then checking LM239 is a non-trivial task. That's why I created the topic.

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