wtf is this weird component? solved, thermistor.  - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 06:40:09 am
content: I am trying to fix something (DSA) and it has this inside of it. I cannot recognize it.It does not look like a battery that I know ofI cannot find the designator for it, the batteries are BT. this does not seem to have a BT nearbyLooks a little like a coin cell but not really.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: March 07, 2021, 06:43:26 am
content: A tortured piezo buzzer maybe?

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 06:44:48 am
content: hmm. it reminds me of a MOV for some reason but its position makes no sense

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 06:46:07 am
content: the in circuit resistance is 8 ohms.so that does sound like an audio thing ?why is it trashed, the rest of the circuit is pristine, save for some crusty dip sockets

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 07, 2021, 07:00:47 am
content: What's it wired to, AC power maybe? Could be an NTC. 8 ohms might be healthy. See if it drops when heated.Haven't seen an uncoated one since... vintage TV sets maybe, I think? Or maybe that all burned off somehow, yeech.Tim

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: March 07, 2021, 07:09:32 am
content: Silver-plated copper sometimes corrodes weirdly, and without needing an electrolyte ... may be triggered by sulfur outgassing from plastics.

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 07:42:01 am
content: it only has DC power input from a regulated supplythe power draw is ~400mA to a linear regulator. I will try to trace the circuit before heating it

author: t0m
author_rank: Regular Contributor
timestamp: March 07, 2021, 07:42:30 am
content: VL2020 maybe

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 07:43:59 am
content: no, it does not have the typical coin cell profile I don't think, and it reads real close to 8ohms, not a coincidence I think.It looks nothing like the picture of a VL2020The outline for it looks like a rectangle also, it does not match the pcb silk screen (it is small in comparison, so its overloading the artwork). It looks like 2 things set in a ring, not like a crimped coin cell, the outer radius is very geometrically nice, looks like it was taken out of a mold or something. The other cell in this thing is a renesas fully encapsulated one in a orange plastic box with a bunch of epoxy, it makes no sense that the designers would go crazy for 1 coin cell but not the other one in terms of safety/reliability (the other one is swiss made!). And it already has a 3Vaa battery and a coin cell, i don't think it would have 2 coin cells. 3 batteries on 1 pcb?? It is also across the entire PCB from the voltage input.the dimensions are 3.5mm by 16 mm measured with a machinists rule

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 07:51:10 am
content: I decided to pull it off the PCB double sided tape because it looks like a huge piece of shit anyway, the designation underneath is TH1. The batteries are designated BTxSo thermistor 1 makes sense? This unit was powered by NICAD batteries.

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2021, 07:56:05 am
content: i put a little bit of solder on top, it dropped to 7 ohms, so it is maybe a NTCany ideas on a part number? Do you think this thing is fine?The problem I am troubleshooting is intermittent turn off, I thought it was crashing because both batteries are totally dead, so I thought to replace those first.Not sure what a peizo buzzer does when measured, but I thought they would be high impedance, so if its 8 ohms, with a 10% chance in resistance from a little bit of heat, it is the main contributing circuit element to the low resistance in the circuit I think. I am a little scared of desoldering it because of how it looks. It fits the description of a RTC device without a coating.I guess it used to look nice and something took it out. When I replace the batteries I will measure it with the device turned on to see if its contributingIt powers off after it is turned on for a little bit, I am not exactly it is correlated to on time , but when it turns off, you do need to wait a little bit before it can turn back on, but I thought it was something to do with a dead battery and charge draining or whatever. The amount of time it has before it turns off is a little random.