What is this mystery component? - Page 1
Forum section: electronics / beginners

author: Chalky
author_rank: Regular Contributor
timestamp: February 16, 2013, 12:25:17 am
content: What is this? Some sort of RF choke? This is from the video circuit section of an old home computer.Cheers! Any responses welcome, including 'I have no idea' - cause that's what I have!

author: Anquietas
author_rank: Regular Contributor
timestamp: February 16, 2013, 12:43:16 am
content: I am absolutely not competent to answer this question, but my random guess would be some sort of ferrite core inductor operating as a filter?

author: c4757p
author_rank: Super Contributor
timestamp: February 16, 2013, 12:46:19 am
content: Since it's labeled "T101" I'd guess it's a small transformer.

author: FenderBender
author_rank: Super Contributor
timestamp: February 16, 2013, 12:49:08 am
content: I was going to say check the silk screen. I would agree. Looks like there might be some different taps.

author: Chalky
author_rank: Regular Contributor
timestamp: February 16, 2013, 04:48:11 am
content: Hmmm yeah am digging in a bit more, I thought transformer too, but checking pins just now shows 9VDC at one pin (straight from power supply) so since DC guessing it's not a transformer. Inductor thingy answer sounds good.

author: smashedProton
author_rank: Frequent Contributor
timestamp: February 16, 2013, 05:10:57 am
content: if you want, pull it off the board and connect it to an oscillator. If you get spiking its an inductor

author: SeanB
author_rank: Super Contributor
timestamp: February 16, 2013, 05:43:44 am
content: Small pot transformer. Probably used to make some other low power rails for use in the computer. I would guess it makes a -20V rail and a +15V rail for the analogue devices on the board. If there is a VFD display then this makes the 2V supply for the filament and the -30v rail as well for it.

author: codeboy2k
author_rank: Super Contributor
timestamp: February 16, 2013, 05:58:53 am
content: Quote from: Chalky on February 16, 2013, 12:25:17 amNo, we're serious. It's a transformer.

author: amyk
author_rank: Super Contributor
timestamp: February 16, 2013, 06:01:18 am
content: You can see one of these in this video at around 43:50:http://youtube.googleapis.com/v/_65erGXqXZk

author: Chalky
author_rank: Regular Contributor
timestamp: February 16, 2013, 07:12:17 am
content: Cheers, will have a look. Ok, call me dumb, but I thought transformers were only AC - I understand the theory of those - so how can you have a DC transformer?

author: Bored@Work
author_rank: Super Contributor
timestamp: February 16, 2013, 08:03:29 am
content: Quote from: Chalky on February 16, 2013, 07:12:17 amBy first chopping the DC into some AC by switching the DC on and off. It is called switch mode power supply (SMPS).

author: TerraHertz
author_rank: Super Contributor
timestamp: February 16, 2013, 08:11:38 am
content: Quote from: Chalky on February 16, 2013, 07:12:17 amJust because it has a DC voltage on a pin, doesn't mean the current through that winding is constant.Maybe that's a positive supply rail, attached to one end of a winding. And the other end has a transistor or MOSFET to ground, and a flyback diode. Viola, DC to DC converter.But it's a little more complicated; at least 5 connections.

author: Chalky
author_rank: Regular Contributor
timestamp: February 16, 2013, 10:44:29 am
content: Ah, right. Yes, thanks heaps for that, does seem to be transformer for DC-DC converter. Can see transistors and inductors close by. Can't see a full-wave rectifier on the other side though, but I do see diode & large electro cap, so maybe just a half-wave.Great, thanks again!

author: Chalky
author_rank: Regular Contributor
timestamp: February 20, 2013, 10:29:40 am
content: Fantastic! Thanks to everyone. It is indeed part of a DC-DC (+9 in, +12 out) converter (found a circuit diagram and someone off-board helped me). Have now determined rough location of a fault on that PCB and proved I can remove the DC-DC converter circuitry and feed in 12v directly to power that PCB, working like a charm. Thanks.

author: hlavac
author_rank: Frequent Contributor
timestamp: February 20, 2013, 01:12:56 pm
content: Quote from: Chalky on February 16, 2013, 10:44:29 amDCDC converters use different topologies, only a few of them would use a full bridge on the secondary. It's often just a single diode on the secondary.

author: brainwash
author_rank: Frequent Contributor
timestamp: February 20, 2013, 02:40:04 pm
content: Is this some IR transceiver?It has 8 surface mount pins, 1&2&4&5 are tied to GND, 3&8 to 5V, 6 seems to go directly to a uC, 7 goes to a low side switch which seems to pull down a uC leg.I would like to know if it's just a plain diode and transistor or if it works with some carrier.For information only, this sits on the top of a coffee machine which I'm taking apart (Saeco) so I either assume it's some sort of IR for optional remote control (I don't think it has such an option), a proximity sensor (not implemented) or some serial communication for servicing. The machine still works (or worked), I'm just hacking it to make it better since it has a lot of software design flaws.

author: senso
author_rank: Frequent Contributor
timestamp: February 20, 2013, 03:23:12 pm
content: Looks like some of this Vishay IrDA transceivers:http://www.vishay.com/ir-transceivers/list/product-81965/http://www.vishay.com/ir-transceivers/list/product-81288/http://www.vishay.com/ir-transceivers/list/product-84763/http://www.vishay.com/ir-transceivers/list/product-84676/

author: brainwash
author_rank: Frequent Contributor
timestamp: February 20, 2013, 03:37:36 pm
content: Thanks, I think you are right. Who still uses IrDA these days anyway? I mean consumer stuff.

author: SeanB
author_rank: Super Contributor
timestamp: February 20, 2013, 05:42:47 pm
content: A lot of cellphones still have it around.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 18, 2013, 11:46:03 am
content: I don't want to open a new thread, so I have a couple more:- a TO-92 transistor looking like thing, labeled "131-6 BJ 028" acting like a low-side switch for a 220V/0.1A load. "Gate" is driven through a "189" SMD resistor, 18 megaohms?- a capsule sitting on top of a heating element, inline with line voltage (220V), labeled "3FME04 20219 L105C V1046". I suppose it is a fuse that blows up at 105 degrees?- maybe pushing my luck, but a sealed NTC labeled 1048 with 11k@19C and 6.5k@30C; would be nice to find out if there is any curve for it

author: brainwash
author_rank: Frequent Contributor
timestamp: March 18, 2013, 12:53:14 pm
content: It just happens that on the entire board this one SMT resistor was upside down. So it's value is actualy 680 ohms, which makes more sense. Luckily the "1" digit has the small upper line still visible.Still no idea what that component is, maybe an SCR with the pins T1/G/T2 instead of the more usual T1/T2/G. Maybe a MOSFET in TO92 package? It doesn't make much sense in AC. Bipolar transistor would be unusual since the gate/trigger is sitting at 5V and the rest at 220V with no connections in between.