Fluke Multimeter

[PeteVee]

I've been using an Ideal 61-314 DMM for a few years. When working on guitar amps I often test capacitors in circuit and get a "close enough" reading, just to see if the capacitor is still in the ballpark and hasn't gone bad. I figured I needed a better meter for testing plate current etc., so I bought a used Fluke 175. With the Fluke I can't test caps in circuit, I get either OL, 0 nF, or the reading jumps around in an apparently random fashion. Is something wrong with this meter or is it to be expected (ironically) with a high end meter?

 

[73's de Edd]

Ya gotta pull 1 cap lead out of circuit to be able to test , fully out of circuit, otherwise you got all potential parallel or series shunted variants in the involved circuit.

 

[PeteVee]

Yeah, I kind of expected that answer, and thanks, but it doesn't really address my question. I know as rule you have to test out of circuit. But as I said, with the circuits I'm dealing with I can often get a ballpark reading on the cap in question without removing from the circuit when using the Ideal meter. Not so with the Fluke. So the question again is, is this to be expected with the Fluke or is there possibly something wrong with it?

 

[Richard9025]

To check if the capacitors (over 1uF) are good in circuit you need an ESR meter , see this topic : https://www.eevblog.com/forum/begin...o-test-capacitors-while-on-the-circuit-board/ . In a circuit you can't get a reliable capacitance reading , sometimes in the "ballpark" sometimes not . To check if your new fluke is good , just test another capacitor out of the circuit

 

[davenn]

. Not so with the Fluke.

and you will find "not so" with most other brands not just Fluke
I am surprised you other meter will give a useable reading of a cap in circuit

 

[PeteVee]

I am surprised you other meter will give a useable reading of a cap in circuit

Swear to God.

 

[davenn]

Swear to God.

even my dedicated Capacitance meter ( it does nothing else) wont measure in circuit

 

[PeteVee]

even my dedicated Capacitance meter ( it does nothing else) wont measure in circuit

Well to be clear, I'm not saying it's fool proof or highly accurate, and certainly it won't work in certain situations e.g. where there are other components in parallel, but more often than not it gives me a reasonable indication of whether the cap is healthy or not.

 

[73's de Edd]

Sir PeteVee . . . . .

I just noticed that my 24" crystal ball was throbbing in intensity as I was reading . . . . Now if there is a good possibility that you are mostly dealing with tube amplifiers the have very high vaues of resistors .
If they ended up shunting connections tied into that tested capacitor circuitry there wouod be minimal interference.
The worse case I could think of, would be is testing a cathode by pass capacitor, which typically has a lower resistance shunting it.
Of my 8 or so FLUKES, of which which I have, both the 10 and 12 series, which were being the only ones which had capacitance handling functions.

Any one out there still running a FLUKE differential voltmeter . . . . which was GOD's gift of accuracy back in the '60's ?

73's de Edd

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