I have come across a bunch of blue axial capacitors that are rated with µM instead of µF. They are those typical crappy blue Philips caps used in their old CD players. In one of my other machines, I have all the same caps, with the same ratings, but in µF. I cannot find any µM caps at my suppliers, so I am guessing this is a term no longer used?
They are 47µM 25V & 2µM 63V. Is µM just another way of saying µF?
TIA
They are 47µM 25V & 2µM 63V. Is µM just another way of saying µF?
TIA
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Measure one. I haven't seem M for 1000 in anything under 50-60 years old. I recall schematics for amplifiers from the 1940-1950s where a 500k pot would be labelled 500M.
So I just measured these. The 47µM 25V measures as 22.5µF 25V. (measured 2 of them to make sure)
The other which says on the cap 1µoM 63V (021 K0) measures as 1.2µF 63V.
So I guess I will be ordering 22µF 25V & 1µF 63V
The other which says on the cap 1µoM 63V (021 K0) measures as 1.2µF 63V.
So I guess I will be ordering 22µF 25V & 1µF 63V
Maybe he meant reform? That would only help get the leakage down. If capacitance is down to less than half as it would seem to be on the 47µs, part of the electrolyte is just gone (evaporated). (It might still affect a cap measurement depending on how the multimeter / component tester does it.) Anyway, if those are some of the same Philips axials I've got, they will go leaky even when just gathering dust on the shelf - clearly the chemistry left something to be desired.
In any case get the values printed on them.
In order to properly assess the health of an electrolytic cap, all the following has to be measured:
1. capacitance
2. ESR
3. leakage current at nominal voltage
If ESR is through the roof but leakage seems fine, I'd suspect a case of bad seals. Often you will find multiple of these parameters out of spec - in which case I would suspect that excessive leakage led to internal heating and subsequent accelerated evaporation.
Fortunately capacitor manufacturers were eventually clued in to the fact that 1/f noise on the leakage current is a good indicator of defects in the oxide layer.
In any case get the values printed on them.
In order to properly assess the health of an electrolytic cap, all the following has to be measured:
1. capacitance
2. ESR
3. leakage current at nominal voltage
If ESR is through the roof but leakage seems fine, I'd suspect a case of bad seals. Often you will find multiple of these parameters out of spec - in which case I would suspect that excessive leakage led to internal heating and subsequent accelerated evaporation.
Fortunately capacitor manufacturers were eventually clued in to the fact that 1/f noise on the leakage current is a good indicator of defects in the oxide layer.
I would if they existed. That is the problem. As for the measurements of the caps I am replacing, the measurements should be accurate as these caps are still good. They are being replaced in a perfectly working machine as preventative maintenance along with about 30 other caps.
I finally got a solid answer. 47µM = 47µF in this case. They are measuring at half value because they are dried up/no good.
Apparently µM is not actually µM but is its µ space M and the "M" is the tolerance. So, its 47µ.
Apparently µM is not actually µM but is its µ space M and the "M" is the tolerance. So, its 47µ.
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Yes, of cause.
I have seen that capacity changes too without reforming.
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Indeed, M is standard marking for 20% tolerance (totally appropriate for electrolytic caps)