avr 7300 harman kardon receiver? - Page 1
Forum section: electronics / repair

author: roauld55
author_rank: Newbie
timestamp: July 05, 2015, 10:57:15 am
content: 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!

author: TimFox
author_rank: Super Contributor
timestamp: July 05, 2015, 04:30:34 pm
content: Note that the suffix "J" at the end of the part value means +/- 5% tolerance.

author: flynwill
author_rank: Regular Contributor
timestamp: July 09, 2015, 02:44:50 pm
content: 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 moreI'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.pdf39 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.pdfAnd 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.pdfwith 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.pdfwith the last I would carefully construct the stack with at least 1/4" between the parts to allow for airflow.

author: ElektroQuark
author_rank: Unknown
timestamp: July 09, 2015, 02:52:02 pm
content: What's the problem using one construction version or the other for this aplication?Or is only about availability?

author: divelectservices
author_rank: Contributor
timestamp: July 09, 2015, 03:28:39 pm
content: 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.

author: flynwill
author_rank: Regular Contributor
timestamp: July 09, 2015, 03:39:28 pm
content: 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.

author: divelectservices
author_rank: Contributor
timestamp: July 10, 2015, 12:29:18 am
content: 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.