I have a 10uf 16v SMD electrolytic capacatior that has an esr of 7ohms. The circuit will start working if you heat the cap up. When it is heated its ESR drops to about 4 ohms. I tried replacing it with a standard leaded 25v 10uf cap that I had laying around but it won't work. I then tried a 10uf 16v Talatanium and it wouldn't work either..
The ESR of both of the replacement caps were under 1 ohm. Is this SMD cap supposed to have a somewhat high ESR about 4 ohms?
- Mike
Are you sure you aren't also heating up any near by caps, or other components when you heat the bad cap? The lower the ESR the better. If one SMD cap is bad, there are probably more. Andy Cuffe
snipped-for-privacy@gmail.com
I think I found the problem.. The chart is way off on my ESR meter. It says that a 16v 47uf cap should have a esr of 2 ohms... I tested similar smd caps and they had an esr of about .09 ohms.
Hmm.. It appears that the heat sensitive problem is the large IC on this LCD controler. The problem chip is a Genesis gm2121..
Is it normal for an IC to become heat sensitive?
- Mike
"Michael Kennedy" wrote in news: snipped-for-privacy@comcast.com:
If it's the Dick Smith ESR meter,it says right in the instructions that the chart is only a *guideline*;that different manufacturers and different cap series will have different ESRs.A look at a DigiKey catalog will show you that.
-- Jim Yanik jyanik at kua.net
I was wrong yet again!
I beleive I have isolated it to a few SMT cereamic caps which have no lables on them.. I found if you heat 3 of them up with a soldering iorn the unit powers up. If you power down and hit them with freeze spray it won't power on..
Can you replace tiny SMT cereamic caps with standard through lead ceramic caps? I think I can solder them in, I just don't know if there are any issues with changing them out.
- Mike
Generally, unless there is a space problem, or lead inductance is critical, then yes, you can substitute smd cercaps with conventional multi-layer X5R,X7R or plate leaded caps.
You might find something suitable in the Vishay Mono-Kap range
Space should be my only problem. I would replace them with smd caps, but I don't feel like paying $6 for shipping on some $0.40 caps when I can buy just about any through lead ceramic cap locally.
- Mike
Lower ESR is better. If you are testing the caps in circuit, you might not be getting accurate results. If there are a lot of caps in parallel (like bypass caps on a power supply rail) the in circuit ESR might look ok even though some, or all of the caps are bad. Andy Cuffe
snipped-for-privacy@gmail.com
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