MOV? Resistor? Please help me identify the component - Page 1
Forum section: electronics / beginners

author: drhayes
author_rank: Newbie
timestamp: April 20, 2020, 03:54:24 pm
content: Hi there,I hope this is such a simple question in which I directly disclose how little I know about electronics, which actually is not too much.I'm trying to find out what component this is. It is labeled as R11 and according to the BOM it is a resistor with 1K OHM 1/8W 5%. Measured in circuit it is almost 39 OHM, and if I read the schematics correctly, there is nothing in parallel that should trick my LCR meter into reporting a value wildly different from the specs.Also I have not consciously seen a resistor in that form factor.So, please enlighten me: what is it?

author: Manul
author_rank: Super Contributor
timestamp: April 20, 2020, 04:23:20 pm
content: It is labeled RT1 and looks to me a thermistor.

author: drhayes
author_rank: Newbie
timestamp: April 20, 2020, 04:26:20 pm
content: Thank you, that explains a lot...Oh dear, I didn't think I would display that much ignorance on my first post.

author: wraper
author_rank: Unknown
timestamp: April 20, 2020, 04:28:52 pm
content: It's JNR-10S100L NTC for reducing inrush current. You should check circuit after it, quite likely it failed because of other failure. Like shorted MOSFET.

author: drhayes
author_rank: Newbie
timestamp: April 20, 2020, 04:36:59 pm
content: Perfect, thanks!

author: Gyro
author_rank: Super Contributor
timestamp: April 20, 2020, 06:24:26 pm
content: NTC thermistor damage like that (sounds like partial failure) can sometimes occur if the mains input is cycled several times in quick succession, without allowing it time to cool down. This can increase peak surge current beyond what it can handle, and of course also exposes the rectifiers to higher than expected stresses.You will obviously know if you have been repeatedly cycling the power but check for things like intermittent mains connection.

author: drhayes
author_rank: Newbie
timestamp: April 20, 2020, 06:50:32 pm
content: Great hint, thanks.But I don't know how the poor, badly designed power supply has been treated. It's from an Alesis M1 Active 620 (apparently known for crappy caps). I had bought it under the premise that it had just died, but somebody already had a go at it.Now that I have more time than I would like to, I started sorting out all electronics. If it's broken I'll either repair it or throw it out. And that one was here for 7 years now. When I saw that someone had tinkered with it (and obviously had even less knowledge than me), I put it on the pile 'for later'. In the meantime - mainly thanks to eevblog - I learned quite a bit in terms of trouble shooting and repairing (meaning: I have an idea which parts of a circuit are dangerous and I know how to replace parts that measure bad). So now is the last chance for the Alesis. I have to repair some traces, correctly replace the blown C8 cap, possibly replace other parts (definitely RT1)...Anyway, I actually wouldn't have checked the mains connector, thanks for the explanation!

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 21, 2020, 08:34:19 am
content: If there is much stress on that NTC one can consider of using a one step larger size thermistor. But it isn't safe, it needs some measurements, calculations and precautions too.

author: drhayes
author_rank: Newbie
timestamp: April 21, 2020, 09:23:47 am
content: Yeah, thanks. But I won't go much deeper with this one, it's just not worth it. So the parts will be replaced with those from the original spec, and if that is not enough, the whole shebang goes into the trash.