LAN tester with burned IC - Page 1
Forum section: electronics / repair

author: Zlobnick
author_rank: Newbie
timestamp: May 25, 2024, 08:46:32 am
content: Hello! I have this LAN tester that got burned out by PoE voltage. This is a newer version than most common ones being driven by a classic CD4017 decade counder IC (16-pins).Has anyone any ideawhich IC is being used here(it is unmarked, of course)? It's a14-pinin SOIC14 package (if I'm not mistaken).Btw, these testers go for a 3-4 bucks on Aliexpress but would like to fix it anyway, for fun and for good practice! 🙂 Thanks!

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: May 25, 2024, 10:11:52 am
content: Do you really plan to desolder SMD components on a bakelite PCB ?

author: Zlobnick
author_rank: Newbie
timestamp: May 25, 2024, 10:16:12 am
content: Quote from: Coordonnée_chromatique on May 25, 2024, 10:11:52 amYeah, why not? Not with the hot air station of course, this should be a pretty easy job for a soldering iron

author: Manolo Mos
author_rank: Contributor
timestamp: May 25, 2024, 11:13:23 am
content: To remove SMD IC on bakelite pcb... I'd remove it adding tin and then remove with two tin soldering irons.

author: daisizhou
author_rank: Super Contributor
timestamp: May 25, 2024, 11:51:00 am
content: It looks like this chip is from China because there is no stamp on it

author: mariush
author_rank: Super Contributor
timestamp: May 25, 2024, 12:33:34 pm
content: To desolder that chip, I'd either add solder on each row of pins to the point where all pins in a row are joined together then alternate heating the rows with soldering iron until the chip can be moved OR I'd just use flush cutters to cut the contacts at the base of the package and then desolder the leftover pins one at a timein theory you could extract the chip inside the package to figure out what it is ... not sure it's a microcontroller because they usually have voltage and ground on pins 1 and 14 while this one seems to have ground pin in the center of the rowYou could get a cheap micro (14-20 pin and put it on a soic to dip adapter board and then glue the board to the existing board and use thin wires to make the connections to the original traces - you can scrape the coating from existing traces to solder to those traces.

author: Traceless
author_rank: Frequent Contributor
timestamp: May 25, 2024, 01:05:34 pm
content: I just took mine apart, it looks completely different and uses two unmarked 16 pin ICs, I guess one is for testing RJ45 network cables the other one for testing HDMI. If you have a programmer like the TL866II, T48 or sth. similar you could get another working unit like your broken one, desolder the IC and try to auto-detect and dump it. If that works you could get a matching blank chip copy the ROM over and try to revive the defective unit.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: May 26, 2024, 09:15:12 am
content: Quote from: Zlobnick on May 25, 2024, 10:16:12 amPlease, show the final result of the rework.The heat resistance of the bakelite is low and the risk of delamination is very high i will be really pleased to see your extreme soldering skills !

author: Zlobnick
author_rank: Newbie
timestamp: May 26, 2024, 09:52:52 am
content: Quote from: Coordonnée_chromatique on May 26, 2024, 09:15:12 amIf I ever get that chip identified I'll make a video just for you, maybe you can learn something

author: mikerj
author_rank: Super Contributor
timestamp: May 26, 2024, 10:02:50 am
content: Quote from: Coordonnée_chromatique on May 26, 2024, 09:15:12 amIt really depends on the quality of that specific board. Some SRBP PCB's are quite robust and easily reworked, while others have the copper lifting off with minimal heat applied.

author: daisizhou
author_rank: Super Contributor
timestamp: May 26, 2024, 10:20:55 am
content: It is easy to solder using a hot air station. The key is to determine the exact model of the chip. I guess it may be a microcontroller chip with a program.

author: Traceless
author_rank: Frequent Contributor
timestamp: May 26, 2024, 10:29:14 am
content: Quote from: mikerj on May 26, 2024, 10:02:50 amTrue, but looking at the board even if the traces lift around the IC they all run on the surface layer are clearly visible, lead spacing is relatively large so it can easily be bodged in case of disaster. Just epoxy the replacement IC to the PCB and run bodge wires to the connected components.

author: Traceless
author_rank: Frequent Contributor
timestamp: May 26, 2024, 10:34:40 am
content: Quote from: daisizhou on May 26, 2024, 10:20:55 amYeah that's what I thought too, in this case reading the chip od an intact unit with a T48 could shed some light on the case. On second thought though maybe we think to complicated and the chip is maybe something simple like aSN74LS90?

author: shapirus
author_rank: Super Contributor
timestamp: May 26, 2024, 10:48:01 am
content: Knowing which pins are VCC and GND could help (at least to filter out the ICs that don't match). It's not quite clear from the photo: the GND (power negative) trace goes to under the IC, and it's not clear where the battery plus trace starts, as the power positive terminal is covered by that plastic cap.

author: kripton2035
author_rank: Super Contributor
timestamp: May 26, 2024, 10:59:17 am
content: 74LS90 is 16 pins ...

author: Traceless
author_rank: Frequent Contributor
timestamp: May 26, 2024, 11:03:31 am
content: Quote from: kripton2035 on May 26, 2024, 10:59:17 amAccording to the Texas Instruments link i posted above it is a 14 pin IC

author: ArdWar
author_rank: Frequent Contributor
timestamp: May 26, 2024, 11:04:01 am
content: Pin 4 VCC and Pin 11 GND.Pretty sure single chip solution for this kind of gadget is a MCU.Looks like the chip is just painted over, maybe some application of various chemical can help. If they didn't sand it first ofc.

author: Traceless
author_rank: Frequent Contributor
timestamp: May 26, 2024, 12:52:54 pm
content: Okay I found two sources that claim that the IC might be an "SAM8928". Here someone posted aschematic(note the SAM8928 in the BOM links to an SN74AHCT02D which has a different pinout, I guess they just used that one for the SOIC-14 footprint and renamed it). Onthis pagesomone analysed and modified different version of those testers.A quick google search did not yield any sources for that IC.Cheers Traceless

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: May 26, 2024, 01:01:10 pm
content: Quote from: Zlobnick on May 26, 2024, 09:52:52 amI've never seen a clean multipin chip SMD rework on a cheap bakelite board, this is a real performance and i think that you shoud share it with everyone

author: madires
author_rank: Super Contributor
timestamp: May 26, 2024, 01:16:18 pm
content: It's quite easy with the right tool, i.e. soldering tweezers with tips for SOICs.

author: magic
author_rank: Super Contributor
timestamp: May 26, 2024, 01:40:14 pm
content: The chip clearly contains both an oscillator and a counter, and apparently pressing the button even puts it into a "slow" mode.Sounds like it's some dirt cheap Chinese microcontroller with appropriate firmware. Even if you could somehow identify and buy the MCU, it's still worthless without the code.

author: madires
author_rank: Super Contributor
timestamp: May 26, 2024, 02:27:03 pm
content: Why so pessimistic? It would be a nice weekend project with a simple circuit and a bit of coding.

author: amyk
author_rank: Super Contributor
timestamp: May 28, 2024, 02:18:51 am
content: According tohttps://electronics.stackexchange.com/questions/34447/can-anyone-identify-the-microcontroller-on-an-hc-sr04that pinout could be EM78P153S or similar series:https://i.sstatic.net/Pz8cD.png

author: Zlobnick
author_rank: Newbie
timestamp: June 26, 2024, 11:39:21 am
content: Thanks a lot everyone, I'll definitely post the results if I ever get it working