ZX-1A MET LABS, cordless AC coolant leak sniffer - power issues  - Page 1
Forum section: electronics / repair

author: PiotrMisiuna
author_rank: Contributor
timestamp: September 02, 2017, 10:56:35 am
content: Device had issues with power supply.Device does not work without a battery, and the power supply does nothing when connected.When connected to a new power supply, power supply triggered over current protection and after few tries the device released a magic smoke.The component that got smoked is a small 8 pin smd right next to the battery connector.I searched allover the web for those symbols, even International Rectifier search gave me no results.it is P843T, H4N0_ , F**9 - look attached photosAny idea what I can replace it with?

author: SMdude
author_rank: Frequent Contributor
timestamp: September 02, 2017, 02:08:37 pm
content: Bugger! Don't you just hate it when that magic smoke escapes!Now, firstly, I am curious as to what voltage the original adaptor is, and what voltage the adaptor was you let the smoke out with and was the polarity correct? I only want to know this so it gives me a good idea of the silly things that consumers do! I hope I have accounted for whatever you did in my productsI don't like things that let the smoke out too easily!Are you able to remove the fet and take a good photo of the traces underneath?I couldn't find anything useful with the available numbers, but I suspect that it could be a dual N fet such as irf8736.Cheers

author: PiotrMisiuna
author_rank: Contributor
timestamp: September 02, 2017, 04:49:30 pm
content: Damnt! I can't believe it. How can I do this stupid mistake again. Center pin of the round power plug goes to the negative battery connector.Silkscreen under the smd is Q401, so it must be some kind of transistor.I got it "passed to me" on a dive with no charger. It wasn't open before me. One diode was shorted, Bateries are NiMh 4.8 so I used a generic usb charger, whei it died I hoocked PC PSU, you know the rest.Thank you for the quick response!

author: SMdude
author_rank: Frequent Contributor
timestamp: September 02, 2017, 11:50:04 pm
content: Can you please tell me the part number of U401.To me it looks like max1540, but I cannot find it listed in that package.The IC that let it's smoke out is a dual Mosfet and it is looking like it is a dual N mosfet.The Mosfet switches the power input to the device from the battery supply to the AC supply when an adaptor is plugged in.Judging by the footprint of the fet, this one should work DMN3018SSD, but it would be nice to find the datasheet for the MAX chip that controls it so we can confirm exactly how it is working.Now, the next thing, I wonder how well the leak sniffer even works. I have one and it's not worth the batteries that power it, so I just keep it for auditing purposes because we need to have it by law.I have never found a leak with one that I couldn't already see/hear.And for those sneaky leaks, charge the system up to 350psi with nitrogen. You will find the leakCheers

author: PiotrMisiuna
author_rank: Contributor
timestamp: September 03, 2017, 07:18:55 am
content: It is max 1640http://pdf.datasheetcatalog.com/datasheet/maxim/MAX1640-MAX1641.pdfI don't work professionally with AC, but I work for a real estate owner and we have at least 40 AC instalations on the buildings.If it worked, that would be a useful add-on, since we outsource all the AC jobs.

author: SMdude
author_rank: Frequent Contributor
timestamp: September 04, 2017, 01:54:31 am
content: Ok, looking at the datasheet, the fet is a dual N/P fet, irf7309.However, the Max1640 is probably toasted due to the reverse polarity and the reverse polarity is also what killed the diode as it is used as a shunt.First thing I would do is see if the correct battery voltage is present, does the unit fie up?Anyway, that will give you something to go by.For the parts, element 14 have both of them.Cheers