Need help identifying this component, SMD fuse perhaps? - Page 1
Forum section: electronics / beginners

author: Turrican3
author_rank: Regular Contributor
timestamp: November 27, 2022, 07:43:56 am
content: Hey there,I have never seen this stuff nor the symbol on the schematic. A quick Google search plus the way they sit on the schematic MIGHT suggest they're fuses but I'm definitely not sure, and assuming at least one of them is actually gone I'd like to repair the board with the right replacement.Could someone please help me identifying the components so that I know what to look for when purchasing spares?Thanks.

author: LateLesley
author_rank: Frequent Contributor
timestamp: November 27, 2022, 05:51:37 pm
content: Yeah, PS may suggest they are polyswitches - or poly fuses, a type of resettable fuse.https://www.littelfuse.com/products/polyswitch-resettable-pptcs.aspxGive me a few mins, and i'll see if i can find that particular one.Edit : Ok, I cannot find that particular one. SO I'd be guessing at the value, possibly 1A , might be 1.4A It's hard to tell the package size too, you'll have to measure it.You might find a suitable replacement here -https://www.littelfuse.com/products/polyswitch-resettable-pptcs/surface-mount.aspxIf the schematic comes with a list of the parts, it might help find the right value.

author: Turrican3
author_rank: Regular Contributor
timestamp: November 27, 2022, 06:16:06 pm
content: Thank you so much!I think I found the full service manual, the part is called "link" (?) by Sony and I honestly have no idea why, but at least I can see the specs, seems to be a 1.4A 24V part.Should be a 1206 size.Let's see if I can get a few (hopefully cheap) replacements.

author: LateLesley
author_rank: Frequent Contributor
timestamp: November 28, 2022, 09:35:32 am
content: Mouser italy, the closest they have is 1.5A ones, which should do the job.https://www.mouser.it/c/circuit-protection/thermistors/resettable-fuses-pptc/?q=polyfuse&maximum%20voltage=24%20VDC&trip%20current=1.5%20A

author: Turrican3
author_rank: Regular Contributor
timestamp: November 28, 2022, 10:27:53 am
content: Thanks again!I'm a bit unsure about size though: available space is very tight, will those fit, as the 1206 series with the required specs doesn't seem to be available?

author: LateLesley
author_rank: Frequent Contributor
timestamp: November 28, 2022, 11:52:10 am
content: oh! yeah, those are bigger. sorry.Let me see if I can find any 1206 ones.OK, I found one listing on aliexpress for 24V 1.5A resettable fuse, in 1206 size.https://www.aliexpress.com/item/32835545528.html?spm=a2g0o.productlist.0.0.3e7857ecCPcCoF&algo_pvid=5b52463f-57c8-4f8d-b2c5-fbae67ec761e&algo_exp_id=5b52463f-57c8-4f8d-b2c5-fbae67ec761e-0&pdp_ext_f=%7B%22sku_id%22%3A%2265074338638%22%7D&pdp_npi=2%40dis%21GBP%213.46%213.46%21%21%211.49%21%21%402100bde116696363681478785e89f7%2165074338638%21sea&curPageLogUid=Q5rkIrDE7Awchttps://www.aliexpress.com/item/1005001870039184.html?spm=a2g0o.productlist.0.0.6e9a1ac5OEP3xI&algo_pvid=9007992e-dde5-4d6f-ba7c-db0e51a39a91&algo_exp_id=9007992e-dde5-4d6f-ba7c-db0e51a39a91-8&pdp_ext_f=%7B%22sku_id%22%3A%2212000028106434651%22%7D&pdp_npi=2%40dis%21GBP%211.0%210.85%21%21%210.76%21%21%400b0a0ae216696367566068873ea4ff%2112000028106434651%21sea&curPageLogUid=53iMS6QRvo1dI'll keep looking for more, and edit them in if I find them. It's proving hard though, most are 6V rated, not 24V.2nd Edit: I think that's it, they are indeed proving hard to find.

author: Turrican3
author_rank: Regular Contributor
timestamp: November 28, 2022, 11:54:23 am
content: No worries, you've already been extremely helpful!I'm looking for a (hopefully) suitable part too meanwhile, will report back.

author: Turrican3
author_rank: Regular Contributor
timestamp: November 28, 2022, 11:29:44 pm
content: Sorry for the bump but I'm even more uncertain now because I just realized... am I sure about that 1.4A rating?I mean, not being familiar with this kind of component, I was wondering whether that's referred to the current that will "break" the fuse, that I understand it's called Trip Current or not.I see resettable fuses sport another parameter that seems to be roughly half the Trip Current, what if 1.4A is actually the latter? (hence trip current might even be closer to 3A)Perhaps it would be safer to purchase a bunch of different fuses starting conservatively with the smallest value and then see what happens? I definitely don't want to risk ruining this Handycam by choosing a fuse that's too big.

author: LateLesley
author_rank: Frequent Contributor
timestamp: November 29, 2022, 08:53:08 am
content: Well, one thing I was avoiding suggesting, but which may help you, is to get your meter, and measure the current that would flow through that part. just set your current meter high enough (probably 10A) and put the probes on each pad where the component lives, then power on, and see what it draws. It'll probably draw far less than you think, but you don't want a trip current too low, so things like startup current (charging caps etc at first switch on) would trip out the circuit.The meter won't show the initial switch on current, that's where oscilloscopes can come into their own, measuring across a shunt resistor (1Ω or 0.1Ω). A trace could show the initial peak switch-on current, which your meter may miss.

author: Automationforum
author_rank: Newbie
timestamp: November 29, 2022, 09:06:11 am
content: SMD Fuses. A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit.https://automationforum.co/fuse-and-types-of-fuses/

author: Turrican3
author_rank: Regular Contributor
timestamp: November 29, 2022, 09:08:04 am
content: @LateLesleyThanks again, I just saw the previous edit and yes it's definitely not easy to find this stuff apparently!Just one last question if I may ask... regarding the oscilloscope measurement, you mean I should replace the failed component with a very low resistor and probe what happens there when turning the cam on, is that correct?And would it make sense to operate with a current limiting power supply?

author: LateLesley
author_rank: Frequent Contributor
timestamp: November 29, 2022, 09:27:46 am
content: Yes. You know that the voltage across the resistor will scale with the current flow, but you don't want too much resistance, or it'll drop the voltage to the circuit, thus why it needs to be low ohms. Many shunt resistors for measuring current are 75mΩ, some will use 0.1Ω or 0.5Ω in lower current applications. Than minimises the voltage drop to the circuit, while still generating several millivolts across the resistor which can be measured. Then ohms law can be used to work out the current flowing.

author: Turrican3
author_rank: Regular Contributor
timestamp: November 29, 2022, 09:39:29 am
content: Awesome, thank you so much!

author: wasedadoc
author_rank: Super Contributor
timestamp: November 29, 2022, 12:56:35 pm
content: Quote from: Turrican3 on November 29, 2022, 09:08:04 amBe aware that many oscilloscopes, certainly most mains powered ones, have the "ground" of the signal input socket connected to mains ground. If the power supply is also ground referenced it is liable to be shorted when you connect the scope across a shunt resistor in its not-grounded side.

author: Turrican3
author_rank: Regular Contributor
timestamp: November 29, 2022, 01:30:18 pm
content: @wasedadocThanks for the heads up, I'm often still confused by this (after all I wouldn't ask for help here if I wasn't a newbie) so I guess I should be careful...Would powering the camcorder with its own battery (assuming it still works, which I'm definitely not sure of) be safe then? Or perhaps using an UPS for either the scope or the camcorder? After all it should be a very speedy measurement, this thing can leave the PC turned on for 10-15 minutes.

author: wasedadoc
author_rank: Super Contributor
timestamp: November 29, 2022, 03:04:59 pm
content: Quote from: Turrican3 on November 29, 2022, 01:30:18 pmPower the camcorder from its own battery. Do not have any cables connected to it. Work on an insulating surface.Watchhttps://www.eevblog.com/2012/05/18/eevblog-279-how-not-to-blow-up-your-oscilloscope/to learn more.

author: Turrican3
author_rank: Regular Contributor
timestamp: November 29, 2022, 08:48:19 pm
content: Awesome video - as usual.Thanks for the suggestion!