Capacitor that looks like a resistor? - Page 1
Forum section: electronics / beginners

author: Skyfox
author_rank: Regular Contributor
timestamp: February 17, 2018, 09:16:12 pm
content: While I'm not a noob when it comes to electronics, this is definitely a beginner question because I've never noticed this before. Attached is a photo from the motherboard in my Commodore 64. I have to do some troubleshooting and repairs, and noticed this component. It looks like a resistor, has colored stripes like a resistor, but has a green body as opposed to the traditional beige of neighboring resistors and is in spot marked for a capacitor. The service manual indicates this is supposed to be an 82pf cap with 5% tolerance, which the gray-red-black-gold seems to indicate. I had a very hard time finding consistent color coding charts, at least when it comes to the tolerance. Some charts show gold at 5% tolerance, and others show no tolerance indication for that color. I take it the white stripe is supposed to be the voltage rating, but one chart shows that's 3 volts while another chart shows that's 900 volts. There are a few others like this on the board of various ratings.Anyway, is this in fact an axial capacitor? Certain other sources show axial inductors with a green body and stripes like this so I don't know how I'd tell them apart. And does anyone have a reliable color coding chart for this so I know what the colors in the tolerance and voltage lines are actually supposed to be? Thanks!

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 17, 2018, 09:49:24 pm
content: Looks like a capacitor according to this schematic.

author: Nusa
author_rank: Super Contributor
timestamp: February 17, 2018, 09:55:55 pm
content: https://en.wikipedia.org/wiki/Electronic_color_code#Capacitor_color-codingIf that's correct, the white band indicates it met EIA standards.

author: tigr
author_rank: Regular Contributor
timestamp: February 17, 2018, 10:26:35 pm
content: There are such capacitors.SkyfoxYour capacitor is 91pF.

author: Jwillis
author_rank: Super Contributor
timestamp: February 17, 2018, 11:29:02 pm
content: Axial capacitors.I've see a few of these but never really looked at the construction.Are they a wrapped film or cylindrical?

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: February 17, 2018, 11:30:21 pm
content: I knew it! Commodore and it's contraptions were foisted upon us by the KGB!How else could they have known thos capacitors?

author: tigr
author_rank: Regular Contributor
timestamp: February 17, 2018, 11:55:22 pm
content: 151pF.

author: Brumby
author_rank: Unknown
timestamp: February 18, 2018, 12:51:50 am
content: Quote from: tigr on February 17, 2018, 10:26:35 pm91 pFor82 pFI'm inclined towards 82 pF myself. For starters the band next to the white is gold - not brown.

author: tigr
author_rank: Regular Contributor
timestamp: February 18, 2018, 01:11:45 am
content: Well, if 82pf, then it should have been welded on the contrary.

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 01:19:46 am
content: Should read grey,red,black.,gold ,white 82 pf at 5% tolerance.I suspect the white is likely a working voltage rating of 1000v

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 18, 2018, 01:21:08 am
content: Come on!! The red is really just orange that turned kinda red due to age. The grey is grey. That means 83 which is correct because it is C83!!!OK...the third glass of wine is talking now...Seriously, the capacitor below it...the 15 pF. That is shown as 10 pF in the schematic I have. So, the schematic may not be reliable w/r to values. I am voting for 82pF.

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 01:25:43 am
content: Well since we're both seeing double from excessive amounts of vino,I'll just say good luck.Its a 82pf...no really.

author: tigr
author_rank: Regular Contributor
timestamp: February 18, 2018, 01:30:59 am
content: They soldered on the contrary. There is nothing terrible. The difference is 9pF.

author: IanB
author_rank: Super Contributor
timestamp: February 18, 2018, 01:34:22 am
content: There's an easy way to resolve this. Unsolder it from the board and test it with an LCR meter.

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 18, 2018, 01:48:27 am
content: Quote from: IanB on February 18, 2018, 01:34:22 am...always somebody like you in the crowd...

author: Nerull
author_rank: Frequent Contributor
timestamp: February 18, 2018, 01:53:04 am
content: Never trust an non-polarized component to be in a circuit board in a specific direction.If that band is gold and not brown, which the shinyness makes me think it almost certainly is, it can only be read one direction. Gold isn't a valid color for the value.I saw this on a site that sells recapping kits for C64s: "The values originally fitted by Commodore can vary slightly (from their own schematics!). Please check the listed contents of the packs against those on your particular board."

author: Nerull
author_rank: Frequent Contributor
timestamp: February 18, 2018, 02:04:54 am
content: I also note that the schematic has two U31s. I wonder if maybe the C64 engineers weren't entirely sober either.EDIT: Actually, now that I read it closer, they've just split a single chip into separate sections of the schematic so it looks like two chips.

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 02:19:05 am
content: Here's simpler code chart .

author: Brumby
author_rank: Unknown
timestamp: February 18, 2018, 02:48:11 am
content: Quote from: tigr on February 18, 2018, 01:11:45 amIt really doesn't matter. I know you and I would mount it to read with the silkscreen, but this obviously isn't being done on this board. Just take a look at R16 at the bottom right of the photo.

author: Nusa
author_rank: Super Contributor
timestamp: February 18, 2018, 03:53:29 am
content: Quote from: Wimberleytech on February 17, 2018, 09:49:24 pmWell, looking at this service manual (https://www.retro-kit.co.uk/user/custom/Commodore/C64/manuals/C64C_Service_Manual.pdf), I see a cleaner version of your snip from the schematic on the second page 21(there are two page 21's in a row). However, down on the second page 27(ditto), there's the same circuit showing C83 as 82pf. Page 17 explains there are multiple versions of the C64 boards. Guess which one the OP has?

author: Jwillis
author_rank: Super Contributor
timestamp: February 18, 2018, 04:51:38 am
content: Quote from: Nusa on February 18, 2018, 03:53:29 amIs there a Prize? C64 version A (CR)

author: tigr
author_rank: Regular Contributor
timestamp: February 18, 2018, 09:27:38 am
content: Here everything is correct.C624-82pF.

author: Brumby
author_rank: Unknown
timestamp: February 18, 2018, 02:26:21 pm
content: I wouldn't exactly call that "correct".If someone had done that on a silkscreen for me ... I'd be having words.

author: Skyfox
author_rank: Regular Contributor
timestamp: February 18, 2018, 03:45:20 pm
content: Thanks to JWillis for that chart! I'll print it out for the wall in the electronics dungeon (my dank basement). And thanks to everyone for your replies and input. This means all these years when desoldering components from circuit boards for the parts bin, I've been throwing out capacitors that I thought were faulty resistors.To reply to other posts here, that band is definitely gold, not brown. It may not show up very well in the photo but it does appear sparkly. And since it's supposed to be 82pf at 5% tolerance according to the parts list in the service manual, the sequence of gray-red-black-gold is correct. And I have to wonder why they'd put a cap rated for 900v on a board that has at most 12v.Yes, there were multiple versions of the C64 board over the years, and even different schematics for the same board (ie. my board is labeled with artwork/schematic #251137, but the service manual shows schematic #251138 for my particular board). Considering how many bodge fixes there are all over this board, it's clear they were revising the thing all the time. Since my board is dated '83, I used the service manual from '85 for simplicity. I do have the '92 service manual, but the information for my particular board is exactly the same as the '85 manual.And since this all has been a mere curiosity for the purpose of learning, I'm not about to desolder and remove this cap from the board just to test it in an LCR meter. However, I do have a scrap board for parts that I could remove that cap from to test. For science!

author: vk6zgo
author_rank: Super Contributor
timestamp: February 19, 2018, 12:08:52 pm
content: Not only are there capacitors which look like resistors, there are also resistors which look like capacitors.One piece of gear had what looked like a small mica cap .Testing it didn't show it as a capacitor, but as a resistor.Closer investigation revealed the capacitor we thought it was in other spot on the PCB.Further tracing found the original device to indeed be a resistor of the previously measured value.

author: Harb
author_rank: Regular Contributor
timestamp: February 19, 2018, 01:10:46 pm
content: R26 is easy, its 0 ohms .......although there may be some resistance at the left hand end

author: Brumby
author_rank: Unknown
timestamp: February 19, 2018, 02:37:28 pm
content: I always smile at "zero" ohm resistors.They are all outside any percentage tolerance ... unless they are really, really cold.

author: bson
author_rank: Unknown
timestamp: February 20, 2018, 08:11:13 am
content: It probably doesn't matter if it's 33pF or 82pF... the factory probably just used whatever happened to be cheaper the day they placed the order.Similarly, I doubt it matters much what it's replaced with, and 47pF would probably also work just dandy.

author: Skyfox
author_rank: Regular Contributor
timestamp: February 23, 2018, 05:22:14 am
content: R26 is 0? because this board is made for NTSC. If it was made for a PAL system it would have been a 100? resistor. A couple other components would have been different, too.

author: Architect
author_rank: Newbie
timestamp: June 24, 2018, 07:02:57 am
content: Just yesterday I was baffled when my LCR tester said that what I thought was a 8.2 Ohm resistor was in fact a 8.2 pF capacitor. Much the same experience as "Nelson Derks" described in "Mystery Capacitor Type" in eham.net.Anyway, I have several of these creatures in the values 8.2 pF, 39 pF, 68 pF, 330 pF and 1.5 nF. So if anyone needs a few, just drop me a line.

author: Gemman Aster
author_rank: Contributor
timestamp: August 30, 2018, 08:09:47 pm
content: I have an Atari motherboard that is full of identical capacitors to these. Given by the time my 130XE was made Atari and Commodore were the same company I suppose it is unsurprizing they drew from the same stock! In places it also uses what look like tiny SMT capacitors sealed inside glass tubes.Is it acceptable to swap modern ceramic disc capacitors for these old, unusual types?