Magnetic Drill, Component identify. please. - Page 1
Forum section: electronics / repair

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 09:36:55 pm
content: It is in between the 5v reg and the safety switch on the magnet, looks like a resistor but it doesn't measure anything on the multimeter. Please help.

author: fzabkar
author_rank: Super Contributor
timestamp: February 27, 2023, 09:52:55 pm
content: It appears to be a resettable fuse (polyswitch), possibly by Littelfuse.https://www.littelfuse.com/products/polyswitch-resettable-pptcs/surface-mount.aspx

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 27, 2023, 09:53:42 pm
content: Hi Nide1,The unknown part is tied to pin 1 of the 78L05 voltage regulator, which is 'Vout'.So the part appears to be in series with the output of the regulator.For the moment, I don't have a definite answer to your question.Can you locate and take a picture where the other track related to the unknown part goes?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 27, 2023, 09:58:17 pm
content: Good guessing from @fzabkar. The 'X' prefix ressembles the manufacturer' logo of Littlefuse :https://m.littelfuse.com/~/media/electronics/datasheets/resettable_ptcs/littelfuse_ptc_smd_catalog_datasheet.pdf.pdfBut it's a bit weird to put a resettable fuse towards the safety switch on the magnet.A 78L05s' output is already short-circuit protected. So, for the moment, I cannot figure out what was the intend of the designer.Does the 5 V rail beyond the unknown part power other sections of the PCB ?

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 10:21:44 pm
content: As I can make out, not even knowing what a magnetic drill was until today, the 5v goes into the safety switch that comes back to the pcb into a chip, which I can't read the numbers on it except (pic). some kind of programable chip I assume, I'm still waiting for a 110v transformer so I can follow the voltages.

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 10:33:59 pm
content: goes through the safety switch to pin 3 of pic chip.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 27, 2023, 10:52:03 pm
content: Strange design. Still don't plainly understand what is the purpose of putting a rearmable fuse in series with the safety feature.In some very particular cases, it is wise to put a fuse on a low voltage rail if you fear a dead short to ground.But why should a mechanical switch that just sees a current of a few mAs be prone to make a short to ground ?PIC is a family of microcontrollers manufactured by Microchip :https://en.wikipedia.org/wiki/PIC_microcontrollers.It seems there's some conformal coating sprayed on the PCB. Should you want to read the parts values, you may remove it from the top of the parts by using some aceton.[update #1 :typo]

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 11:21:43 pm
content: Thanks for reply timeandfrequency, what do you reckon miss it out and cross fingers.

author: fzabkar
author_rank: Super Contributor
timestamp: February 27, 2023, 11:24:22 pm
content: Why did the fuse go open?

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 11:26:11 pm
content: good question, not sure of the answer.

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 11:29:08 pm
content: not sure how the safety switch works or pic chip shorted.

author: Nide1
author_rank: Contributor
timestamp: February 27, 2023, 11:32:02 pm
content: I'll have to delve deeper tomorrow, thanks everyone.