EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: newtekuser on February 25, 2022, 06:03:45 am
-
Hello all,
I have an old compaq portable I in my possession with a dead power supply, it's is the same power supply that Dave filmed in his video on his YT channel. Visual inspection revealed two blown tantalum 2.2uF 25V caps (C37, C39) close to the comparator circuit, no other caps are bulged but given their age I'm willing to replace them.
I took some of the bigger caps out of circuit to test them and found these values with my DER DE-5000 LCR meter:
3300uF 6.3V reading 3.3mF 0.0ohm ESR @100Hz freq
100uF 250V reading 91.3uF 0.4ohm ESR @100Hz freq
470uF 25V reading 470uF 0.03ohm ESR @1KHz freq
The ESR values above are way off any of the ESR charts I was able to find online (guess it has to do with being older tech, maybe my LCR meter is not sensitive enough) and capacitance values look good to me.
What's the best approach in this case since ESR is undetermined? Should I be replacing them or wasting my money?
I don't understand how a cap can have 0.0ohm ESR, maybe shorted but then how am I reading correct capacitance? Could it be faulty LCR meter?
-
Low is good.
https://www.eevblog.com/forum/beginners/esr-values-for-electrolytic-caps/ (https://www.eevblog.com/forum/beginners/esr-values-for-electrolytic-caps/)
-
The "S" in ESR is "series": it is an unwanted (normally) resistance in series with the capacitance of the physical component. Unfortunately, parallel resistance is sometimes called "shunt resistance" that starts with the same letter.
-
From the original post: "I took some of the bigger caps out of circuit to test them and found these values with my DER DE-5000 LCR meter:"
-
I don't understand how a cap can have 0.0ohm ESR, maybe shorted but then how am I reading correct capacitance? Could it be faulty LCR meter?
"0.0" can mean 0.099 just as much as it can mean 0.000. An ESR in the tens of milliohms is a sane reading for a cap that big.
-
Could it be faulty LCR meter?
Correct
Very likely, as it's uncommon things on component around common markets except few hi-techs ones eg. Proadlizer caps
Must ensure with calibrating it
-
I pulled the datasheet for one of the replacement caps I bought from digikey to test my meter and ESR reading is spot on for the 1500uF 25V cap (part no EEU-FK1E152S) rated for 1.8mA ripple current:
Datasheet impedance: 0.038
ESR meter: 0.03
Capacitance reading: 1433uF
Meter was calibrated using the internal open/short method.
LE: I realize now it said impedance not esr, oh well. Is there a way to obtain the esr value from others in the datasheet?