Capacitor code question

[joelgraff]

I have a few capacitors I'm replacing on an Atari 2600 motherboard.  They're coded and it doesn't quite match what I'm familiar with.  Specifically, they look like old film caps and have ratings as follows:

• 0.068K 100V
• 0.22M 100VF
• F.1K 100V

The "100V" is fairly obvious (though I wonder about the 100VF).  As for the other numbers, I would assume M and K are tolerance references, except the preceding values aren't the usual integer codes.  Looking around, I get a few different possible meanings, one being the 0.68, 0.22, and 0.1 values are in an assumed unit (either micro or pico farads) and the M and K are tolerances, or they're a 0.068 Kilofarad and 0.22 microfarad capacitor, respectively.  As for the preceding "F" in "F.1K", I've no clue.

Anyway, I figure this is an easy one, but weirdly, I'm having no luck getting a clear answer after searching.

[inse]

Kilofarads don't exist today, so much to be said...

[joelgraff]

My bad. I meant thousandths... not thousands...  So milifarads.

[ledtester]

I'm pretty sure they are all in microfarards. The K and M are likely tolerance codes:

https://www.electronics-notes.com/articles/electronic_components/capacitors/capacitor-codes-markings.php

Do you have a way of measuring capacitance? That will give you a ballpark figure. As inse mentioned, K as in kilo as a multiplier would mean a factor of 1000, but milli- and micro- mean 10^-3 and 10^-6 -- way off in the other direction.

For the ".068K" caps used in the paddle circuitry, this blog post says they are 68nF caps:

https://www.skooterblog.com/en/2019/06/30/conserto-de-atari-2600-que-nao-funcionava-com-paddles-problemas-e-solucoes/#:~:text=I%20then%20decided%20to%20identify%20and%20test%20the%20capacitors.

It also mentions a service manual for the 2600. I found one at manualslib.com. It's 156 pages and includes a parts list starting on page 137 of the PDF.

Update: the prefix for 1/1000 is "milli-" -- using "K" wouldn't make much sense.

[MikeK]

Aren't the schematics freely available online?  I would think someone was bound to do it.

[Vovk_Z]

All numbers less than 1.0 are in microfarads (until it is stated another). When we talk about a digital device, usually there is no need to talk about tolerance (mostly).

[joelgraff]

Aren't the schematics freely available online?  I would think someone was bound to do it.

Yes, they are.  But the units aren't noted on them, either.

[joelgraff]

All numbers less than 1.0 are in microfarads (until it is stated another). When we talk about a digital device, usually there is no need to talk about tolerance (mostly).

From your response, it seems most likely the letters indicate the capacitor tolerance, then.

[joelgraff]

Update: the prefix for 1/1000 is "milli-" -- using "K" wouldn't make much sense.

I seem to recall reading that "M" meant micro / millionths on older caps, so if that were the case, "K" would seem reasonable as an indicator of milli / thousandths.  It's not as though anyone would confuse it with a megafarad or kilofarad cap, after all, except me.    Anyway, I could see it used either way, but tolerance codes are probably the answer.

Anyway, I don't have a reliable cap tester, but I'll give the one I have a try and see if maybe it gives me a clue.  Thanks for the links, btw.  I hadn't come across those!

[MikeK]

I seem to recall reading that "M" meant micro / millionths on older caps, so if that were the case, "K" would seem reasonable as an indicator of milli / thousandths.

As ledtester said, K and M are almost certainly tolerance codes. K = 10%, M = 20%

Post here what the schematic says.  Have the knowledgeable people here make the informed guess.

[TimFox]

Update: the prefix for 1/1000 is "milli-" -- using "K" wouldn't make much sense.

I seem to recall reading that "M" meant micro / millionths on older caps, so if that were the case, "K" would seem reasonable as an indicator of milli / thousandths.  It's not as though anyone would confuse it with a megafarad or kilofarad cap, after all, except me.    Anyway, I could see it used either way, but tolerance codes are probably the answer.

Anyway, I don't have a reliable cap tester, but I'll give the one I have a try and see if maybe it gives me a clue.  Thanks for the links, btw.  I hadn't come across those!

Many years ago (1960s), the abbreviation "mfd" meant "microfarads" and "mmfd" (pronounced micky-mikes) meant "micro-microfarads" (pF).

[tepalia02]

I think it will be better if you post a schematic or a  photo.

[metrologist]

I'd like to inject a related tangent. I have SMD tantalum caps with code 10-35 N2. What does the N2 mean? I've seen N1, N2, and N3 codes, and these are the black monoliths not yellow.

And who decided that a line that goes most of the way across these caps and looks like a minus sign should designate the positive pole, instead of how we designate the cathode of a diode with a line?

[free_electron]

Kilofarads don't exist today, so much to be said...

they do. a bank of Maxwell caps.

[free_electron]

I'd like to inject a related tangent. I have SMD tantalum caps with code 10-35 N2. What does the N2 mean? I've seen N1, N2, and N3 codes, and these are the black monoliths not yellow.

And who decided that a line that goes most of the way across these caps and looks like a minus sign should designate the positive pole, instead of how we designate the cathode of a diode with a line?

on tantalums the line is ALWAYS the positive. the black ones are typically made by kyocera , vishay (sprague division) and kemet. the orange ones are siemens, avx and yageo.  now, since acquisitions constantly happen this boundary is now  "soup"

[tooki]

the orange ones are siemens, avx and yageo.  now, since acquisitions constantly happen this boundary is now  "soup"

You don’t say… (Siemens spun off all its component manufacturing back in 1999. So nobody is gonna be buying Siemens caps now. Those would be TDK now.)