Electronics > Beginners

Capacitor that looks like a resistor?

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Jwillis:

--- Quote from: Nusa on February 18, 2018, 03:53:29 am ---
--- Quote from: Wimberleytech on February 17, 2018, 09:49:24 pm ---Looks like a capacitor according to this schematic.

--- End quote ---

Well, 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?

--- End quote ---

Is there a Prize? C64 version A (CR)

tigr:
Here everything is correct.
C624-82pF.

Brumby:
I wouldn't exactly call that "correct".

If someone had done that on a silkscreen for me ... I'd be having words.

Skyfox:
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!

vk6zgo:
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.

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