Capacitor Values

Classic Toy Trains Forum
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Hi! Does anyone know the values of the 2 missing capacitors on this Lionel RCMC board ( there is a large one and a small one missing)? Thanks! BradProcessing: IMG_0715.jpeg…

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Hi! Does anyone know the value of the 2 missing capacitors on this Lionel RCMC board ( small one and large one)? Thanks! Brad

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While you’re waiting for the experts, you could desolder the two ‘existing’ ones and either see the values printed on the wrap or get a multimeter with a capacitor-testing function…

Note the + on the board for each.

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Thanks! I will use a multimeter!

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I’d recommend starting by trying to read anything you can on the sides of the units on the board that has them installed. It’s possible (though not certain) that much of the info may be read without de-soldering the caps from the board.

It looks like very little of the surface of each of these 2 would be obscured totally. A light with a magnifying glass is a better first step than using a soldering iron to remove the components (possibly risking damage to an otherwise good board).

Using a meter (assuming it’s range will properly read the value) can be a problem when the capacitors are still in the circuit, as other components in the circuit may alter your readings. (example, other capacitors in parallel within the circuit would cause misleading readings when you are trying to figure out the value to replace one capacitor)

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Don’t forget…does your multimeter have a CAPACITOR VALUE function? A good or bad capacitor can be tested w/simple multimeter. More expensive meters are needed to measure the value/size of the capacitor. regards mike endmrw1006251406

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I noted he should desolder and remove the capacitor to test it with the multimeter – my language was not clear enough. In any case the meters I have with capacitor test do not use the probes; they require the capacitor leads to be inserted into small sockets on the meter face.

I agree that if he can read the values on the side of the cap while it is still soldered in place he should do so – but if he could, would he have needed to post about it here?

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Good advice Dave.
Especially “testing w/o removal” from circuit, No Good. Bad trouble shooting.
If no success with light/magnifier, I would probably do what Woke suggested…Then again, does Brad have a simple multimeter or more expensive one that measures microfarad values. The “Woke route” is moot IF Brad does not have the proper multimeter. regards mike endmrw1006251420

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I have not checked recently, but as I recall Harbor Freight has relatively inexpensive multimeters with the ‘capacitance test’ sockets, and other inexpensive alternatives are probably available via Amazon. If he does not yet have a DMM, I’d thoroughly encourage him to get one.

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So. The blistering of the lacquer under the caps is not good. Either someone used a big Weller gun to remove them or the board is bad.
Why are they gone? Did you remove them because they blew out the end?
Or is this some random board you picked up somewhere?
TOC
ET(SS)

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Sorry, I wasn’t trying to imply you suggested he measure them in the circuit. I was maybe jumping ahead to what I thought might be the next question coming after Brad said he would use a meter. Too much trying to anticipate the follow-up posts on my part :slight_smile:

While I didn’t think about this aspect originally, now that we are all posing thoughts, even if he did de-solder the caps, would the leads likely be long enough to be inserted into the meter? Normally the leads are clipped pretty close to the board after being soldered in.

Also, good point on Curmudgeon’s part. I didn’t originally notice the funky looking board where the caps are absent, but can’t dispute that in itself is a huge red flag warning how this may turn out.

{edited to change “test” to “measure”}

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so, there a number of posts saying to “test” the good capacitors on the good board?

huh?

they don’t need testing. He’s trying to find the value in microfarads… and you won’t get a cheap multimeter to read that value.

Also you need to know the working voltage, again on the side of the cap along with the capacity.

You can test that for sure, keep raising the voltage until it explodes.. seriously.

So, forget all the testing… you should be able to read the value, and if you cannot then you might try to unsolder it..

But all this begs the fundamental: what caused the bad board to become bad? These caps rarely go bad… so you should determine the cause BEFORE you try to repair.