I could use some help indentifying a component in a audio reciever - Page 1
Forum section: electronics / repair

author: Banthors
author_rank: Newbie
timestamp: May 20, 2022, 03:36:38 am
content: This is the component in question r244fl on the schematic. I looked up all versions of the info written on it and nonthing comes up. Thank you guys

author: james_s
author_rank: Super Contributor
timestamp: May 20, 2022, 03:42:24 am
content: It's a power resistor, although I've never seen one with 3 legs, and I've never seen that schematic symbol either.https://www.made-in-china.com/showroom/kingwahoo/product-detaillqdJutsvbEcg/China-Cement-Resistor-MPR-Type.html

author: octillion
author_rank: Contributor
timestamp: May 20, 2022, 03:47:17 am
content: It's two 0.27 ohm resistors in series, the center leg being the common tap. These are frequently seen in push-pull audio amplifiers.

author: inse
author_rank: Super Contributor
timestamp: May 20, 2022, 04:16:36 am
content: Appears to me, they did not have this special resistor in their CAD library and used a sort of connector instead.Done that myself too, but not for official schematics.

author: TheMG
author_rank: Frequent Contributor
timestamp: May 20, 2022, 06:31:47 pm
content: Yup seen these things a lot, two 0.27 ohm resistors in a single package, with a common terminal.

author: gamalot
author_rank: Super Contributor
timestamp: May 20, 2022, 07:22:20 pm
content: Not the exact same model, but for referencehttp://www.oneresistor.com/wp-content/uploads/2013/07/MPR.pdf

author: floobydust
author_rank: Super Contributor
timestamp: May 20, 2022, 07:29:29 pm
content: I recognize that as a dual rectangular 5W "plate resistor", like Fukushima Futaba MPC series or KoaBPR series.They are commonly used in audio power amplifiers, low inductance flame-proof.One problem is they can fuse and one or both can go open circuit if an output transistor fails, so check their resistance.

author: CaptDon
author_rank: Super Contributor
timestamp: May 21, 2022, 12:58:23 am
content: Why does every designator have 'FL' after it?

author: gamalot
author_rank: Super Contributor
timestamp: May 21, 2022, 06:54:17 am
content: Quote from: CaptDon on May 21, 2022, 12:58:23 am"Front Left" I guess.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: May 21, 2022, 10:13:47 am
content: Although that picture is a .27 ohm resistor at 5W the schematic is showing a different part ? 4.7 ohm to the base of the transistor not an emitter resistor so I think there is a mismatch of part and location.This is not a symbol I have seen used before. What brand is the unit?Jeff

author: mclute0
author_rank: Regular Contributor
timestamp: May 21, 2022, 07:15:01 pm
content: It may not match the schematic spec due to manufacturing changes. If the factory runs out of a certain part and can't get replacements soon enough, they put in a part that will just 'work' and move on with production. As long as the device will last through any warranty period it will save them money.I think the schematic symbol indicates a shielded resistor and the third leg is the shield going to ground, but you can easily test that with a DMM on one of the other similar resistors shown on the schematic. Third legs are also added to components that heat up to help stop solder joint separation from expansion/contraction.good luck.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: May 21, 2022, 08:17:25 pm
content: Hang on a minute,it was clarified earlier that this is a dual emitter resistor, commonly used in audio power amps.That is 2 x 0.27 ohm resistors in one package.Both resistors share the same amplifier output connection in the circuit they are used in, so this is indeed a thing, and has been for decades.

author: mikerj
author_rank: Super Contributor
timestamp: May 21, 2022, 09:12:14 pm
content: Quote from: Jeff eelcr on May 21, 2022, 10:13:47 amYou are looking at R238FL/R239FL which is not the resistor the OP is referring to. R244FL is connected to the emitters of both output transistors and doesn't have a value listed on the schematic. It doesn't use a conventional resistor symbol, looks more like a connector.

author: floobydust
author_rank: Super Contributor
timestamp: May 21, 2022, 09:38:12 pm
content: The emitter resistors are also test points for measuring bias current, so schematics can have arrow bubbles, circles, test points, connectors, pins etc. also drawn at them to make things seem even weirder.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: May 22, 2022, 01:17:41 am
content: Now I see what you mean, still what brand is this and what drew that schematic?Thats two symbols I have never seen used in an audio product by any manufacturer.Jeff