avr 7300 harman kardon receiver?

[roauld55]

Does anyone know where could I find new resistor for my avr 7300 harman kardon receiver?
I believe it is 15W 40 ohm resistor. Please correct me if I'm wrong.




Thanks in advance!

[TimFox]

Note that the suffix "J" at the end of the part value means +/- 5% tolerance.

[flynwill]

Well I'll admit I was a bit surprised when I when through the search engines at the various suppliers and those don't seem to exist any more     I'm pretty sure that style of resistor was "composition" as opposed to wire-wound.  A careful examination of the broken one should tell you.

It might be possible to use a ceramic wire wound:
http://www.mouser.com/ds/2/303/res_tuw_tum-275862.pdf

39 ohms is the standard 5% value and is probably an ok substitute.

Or you can get 40 ohms in the conformal coated wire-wounds like this:

http://www.ohmite.com/cat/res_200.pdf

And you might even be ok with the 12W version instead of jumping to the 20W version.  However being an audio amplifier and not knowing where these are in the circuit, there could be issues from the inductance of the wire-wound parts.

The other choice would be one of these:
http://www.mouser.com/ds/2/62/MP9000_Series-216960.pdf 
with a heat-sink somehow cobbled into the free space above the PCB.

Or, 3 120 ohm 5-Watt Metal oxide resistors wired in parallel:
http://www.mouser.com/ds/2/315/AOA0000CE18-49099.pdf

with the last I would carefully construct the stack with at least 1/4" between the parts to allow for airflow.

[ElektroQuark]

What's the problem using one construction version or the other for this aplication?
Or is only about availability?

[divelectservices]

Those are sand block resistors.  Pretty common in audio amplifiers.
It is important that you replace them with the exact value and wattage rating.
Also they should be replaced in pairs and matched.
40ohms is a relatively obscure and high value for those.  You may have to get them directly from the manufacturer.

I am curious to why are you replacing it?  They rarely fail.

[flynwill]

Look at the OP's picture, one of the pair is cracked clean in half.

The only construction issue is wire-wound vs composition.  Wire-wound resistors have a lot more parasitic inductance than composition ones.  Whether or not the inductance is enough to matter to the circuit is hard to tell.

You may well be right about the pair needing to be matched.  If the OEM parts can be found that's best, if not I would lean towards replacing the pair with modern TO-220 ceramic units on a small heat sink.

[divelectservices]

Wow didn't see the crack!
I would desolder it and check the value...cracks don't always affect the resistor inside.
I have seen ones with chunks missing that are fine.
The inductance should not be too important if these are used on the emitters of the output transistors.
In that case, ceramic resistors should work just fine.