Schematics information - what does NF mean? - Page 1
Forum section: electronics / beginners

author: bitman
author_rank: Unknown
timestamp: December 02, 2018, 05:32:08 pm
content: On the attached schematics from a Raspberry Pi 3, the R56 is missing on my Pi - as it's a voltage divider I'm going to look to replace it. But I'm not sure what the NF means on the diagram? If the "F" is "film" what does the N stand for? I know of Carbon and Metal film - none seem to match. On the other hand, since R56 is 0Ohm I really wonder if I'm on the right track - I've never seen a voltage divider where one of the resistors is 0 - what's the point?

author: capt bullshot
author_rank: Super Contributor
timestamp: December 02, 2018, 05:35:43 pm
content: Guess it's an unknown variant of "no load", "do not populate", ...Wait a sec, my guess would be "not fitted"

author: ruffy91
author_rank: Regular Contributor
timestamp: December 02, 2018, 05:37:52 pm
content: NF means it's not populated and 0 Ohm to Vout means no scaling (so 0.6 to 1.39372V programmable Vout)

author: Nusa
author_rank: Super Contributor
timestamp: December 02, 2018, 05:55:50 pm
content: What they said - not fitted. It's a solder selection mechanism, which could be a voltage divider, but in this case is not. In that context, 0 ohms makes sense.If you look for those pads on the actual hardware, it should be obvious.

author: bitman
author_rank: Unknown
timestamp: December 02, 2018, 07:13:27 pm
content: It's "funny" - I remember reading a few threads on 'missing components' but it never occurred to me that this was that case. See the image of the missing resistor - it looks like solder is on the pads, which is why I thought things were missing. I would expect to see the straight copper if it was just skipped. So I guess it's about solder selection as you stated - unfortunately I'm not sure what that really entails. All I can say is that this is the first time I look at this relatively old RPi (it stopped working) and I see a pretty bad solder job - and I swear that's left over paste on R57.But at least it makes sense now. Thanks.

author: tsman
author_rank: Frequent Contributor
timestamp: December 02, 2018, 07:46:23 pm
content: Quote from: bitman on December 02, 2018, 07:13:27 pmThe solder paste stencil still has the holes for R56 so if they did decide it was necessary, they wouldn't need to make new stencils. It doesn't cost them anything extra to put solder paste onto R56 even though they're not intending to fit something there.

author: Fire Doger
author_rank: Regular Contributor
timestamp: December 02, 2018, 07:58:47 pm
content: With that method you can build and many variants of your board, for ex 5V and 3.3V or more complicated circuits like scopes with function gen or not, etc...Same board, same stencil, only the pick n place file changes, if you had 2 stencils it would be more complicated without any saving on cost.

author: Nusa
author_rank: Super Contributor
timestamp: December 02, 2018, 09:33:48 pm
content: On the flip side, it means the schematics may not match the actual implementation when it comes to values actually stuffed on the board.

author: Brumby
author_rank: Unknown
timestamp: December 03, 2018, 12:47:54 am
content: If someone is on the ball with the schematics, they should have notes to cover that, or possibly insets showing alternate configurations.But if these come from circuit revision, that won't help copies of the schematic already out in the wild.