Repairs for a broad range of sound generating equipment including speakers and speaker components.

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What is an "NF" Carbon Resistor

Hello all, I'm in the process of repairing a liquid damaged subwoofer. (Onkyo 750x) The service manual describes a few carbon resistors as "NF", according to the wiring diagram these specific resistors are for safety purposes. All other resistors are marked as a standard carbon.

I've tried replacing them with the standard 1/4 watt carbon resistor but they just burn up, even with considerably lower power than what is indicated to run the woofer.

Does anyone have a work around? The "specific" part numbers listed in the manual don't help much.

82 ohm - p/n 415478204T

1.0k ohm - p/m 415471024T

Thank you.

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NF can mean Non Flammable or Not Fitted but since they were fitted and are listed in the parts section of the service manual then I think that it means non flammable.

You didn’t say the board component ID of the resistors which are burning out.

Looking at the service manual there are 3 x 82Ω resistors with part #415478204T i.e R511, 513 & 514 and 2 x 1KΩ with part #415471024T i.e. R505 & 506.

I’d be looking for a problem with another component that is common to the ones that are burning out as they all seem to be connected to the same supply rail. (except R514 so assume that’s not one of them)

Block Image

(click on image to enlarge for better viewing)


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@jayeff I wondered if those resistors were originally there or if the OP just replaced them because of being shown on the schematic. :-)



Just posted the service manual (see p.6 above Q501 and Q502 and below Q510) and it shows that they're marked as a "critical safety - replace with specified part number" so I think that they're there ;-)


Awesome! Is there a 0ohm resistor within the same rail? Sorry still at work and they do not let me access my manuals or download to company computers ;-)



Can't see one but if there's a shorted transistor it's possible (depending on which resistors are going).

Posted image of schematic above

What's the matter with them!

Aren't frontline workers allowed some "free time and support at work" to renew and re-invigorate so as to be more productive?

BTW Welcome back ;-)


@jayeff right you are but we had so much turnover and people leaving the profession that they now make the bosses work;-)

It’s really good to be back!




Dmak the definition of something like N/F is most commonly used for “Not Fitted” which is similar to the “no Stuffed” in Apple schematics. There should actually be no component there. Schematics may have a component/value there but those are for the designer who may have some future plans for expansion/different versions. For now consider N/F as no part there. Let’s see the schematics and hopefully that will tell us even more. Adding images to an existing question.


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Dmak crwdns2893898:0crwdne2893898:0

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