Weird ESR readings

[cib3k]

I have an old LG CRT TV from 2001. The image expands when I turn the contrast up, and shrinks when I turn it down. I'm trying to see if I can fix this. I started testing capacitors (in circuit), and I've got some weird readings for 2 of them.

The first one is 160V 100uF. When I try to measure ESR, I get a flashing -0. If I reverse polarity, I get the same -0. If I only touch the capacitor leads for a moment, I get some large values: 50, 90, even 100 ohms.

Using my multimeter to measure resistance on the 20K scale, I get values that increase up to 2.8K and stabilize there. If I reverse polarity, the readings go almost instantly to infinity.

The other capacitor is 250V 4.7uF. It gives no ESR reading. I cleaned the leads, made sure the probes are making proper contact, and I still get no reading. My ESR meter doesn't react at all when I touch the leads. Using my multimeter on the 20KOhm scale, I get values that go up to 11K. Reversing polarity, I get infinity.

Does anyone know how to explain these readings?

[budm]

Re: Weird ESR readings

What do you read when the cap is off the board? I never do ESR testing with cap on board due to other components may be connected in parallel with the cap.

[Alastair E]

Re: Weird ESR readings

Classic symptom of low EHT or very poor EHT regulation.

I would suspect the Line-Output Transformer rather than a cap!

[cib3k]

Re: Weird ESR readings

At the moment I'm just looking around, I'd rather not take components off board unless I'm quite sure they're bad. I prefer analyzing things rather than randomly disconnecting components. I'm a beginner and this way I'm trying to learn more about electronics. Thanks for the transformer tip, I'll look into it.

[Kiriakos GR]

Re: Weird ESR readings

At the moment I'm just looking around, I'd rather not take components off board unless I'm quite sure they're bad. I prefer analyzing things rather than randomly disconnecting components. I'm a beginner and this way I'm trying to learn more about electronics.

In this case you better step away from electronics, because this spesific industry does not use your imaginary methods.

[goontron]

Re: Weird ESR readings

At the moment I'm just looking around, I'd rather not take components off board unless I'm quite sure they're bad. I prefer analyzing things rather than randomly disconnecting components. I'm a beginner and this way I'm trying to learn more about electronics. Thanks for the transformer tip, I'll look into it.

[cib3k]

Re: Weird ESR readings

Come on guys, as I said I'm a beginner. I've read about lifting tracks and irremediably damaging boards, so until I master component removal I stay away from that. And I need some dead boards to practice on. At the moment I'm studying mostly how things work, how to use meters, how to interpret ESR readings and so on. I learn a lot just by testing my TV.

Also, while searching for more info on flyback transformers, I came across an electronics forum where a guy had just fixed the same problem on the same TV as mine by replacing a dried out capacitor. I checked and it was the one where my ESR meter gave that flashing -0 reading. So now I know what this reading means, and how to interpret it in case I stumble upon it again.

[budm]

Re: Weird ESR readings

Since you are the beginner, you should at least get the SCH of what you are working on, see how the suspected bad component is connected in the circuit, see if it has resistors, caps, transistors, diode, etc connected in series/parallel with it. You should also try measuring the spare parts you have and see what the read out are, etc. Build some circuits, take measurement of the part in circuit and off circuit and see the reading results of the reading when component is measured when it is connected to the circuit and when it is not.
Also learn about safety when you work on the equipment.

[Kiriakos GR]

Re: Weird ESR readings

Since you are the beginner, you should at least get the SCH of what you are working on, see how the suspected bad component is connected in the circuit......

Because he is not ready for that part either he is skipping it for now.

[budm]

Re: Weird ESR readings

Yes, he needs to learn the basic first, without good base of understanding of how each components work and know how to apply that knowledge, it will not be easy if you skip. Working on CRT that can have up to 30KV is not something to start with.

[Alastair E]

Re: Weird ESR readings

well--

Recommend you get an old circuit board--from anything--and Practice Removing/replacing parts with solder-sucker and de-soldering braid. and a good reel of 0.5mm LEADED solder.

Forget the Lead-Free CRAP.

That way, you'll gain experience and confidence.

More often than not things HAVE to be removed to test properly.