Author Topic: LAN tester with burned IC  (Read 1107 times)

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Offline ZlobnickTopic starter

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LAN tester with burned IC
« on: May 25, 2024, 08:46:32 am »
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 idea which IC is being used here (it is unmarked, of course)? It's a 14-pin in 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!  :-+




« Last Edit: May 26, 2024, 09:56:46 am by Zlobnick »
 

Offline Coordonnée_chromatique

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Re: LAN tester with burned IC
« Reply #1 on: May 25, 2024, 10:11:52 am »
Do you really plan to desolder SMD components on a bakelite PCB ?
 

Offline ZlobnickTopic starter

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Re: LAN tester with burned IC
« Reply #2 on: May 25, 2024, 10:16:12 am »
Do you really plan to desolder SMD components on a bakelite PCB ?

Yeah, why not? Not with the hot air station of course, this should be a pretty easy job for a soldering iron :)
 

Offline Manolo Mos

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Re: LAN tester with burned IC
« Reply #3 on: May 25, 2024, 11:13:23 am »
To remove SMD IC on bakelite pcb... I'd remove it adding tin and then remove with two tin soldering irons.
 

Online daisizhou

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Re: LAN tester with burned IC
« Reply #4 on: May 25, 2024, 11:51:00 am »
It looks like this chip is from China because there is no stamp on it
daisizhou#sina.com #=@
 

Offline mariush

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Re: LAN tester with burned IC
« Reply #5 on: May 25, 2024, 12:33:34 pm »
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 time

in 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 row

You 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.
 

Offline Traceless

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Re: LAN tester with burned IC
« Reply #6 on: May 25, 2024, 01:05:34 pm »
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.
 

Offline Coordonnée_chromatique

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Re: LAN tester with burned IC
« Reply #7 on: May 26, 2024, 09:15:12 am »
Do you really plan to desolder SMD components on a bakelite PCB ?

Yeah, why not? Not with the hot air station of course, this should be a pretty easy job for a soldering iron :)

Please, 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 !
 

Offline ZlobnickTopic starter

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Re: LAN tester with burned IC
« Reply #8 on: May 26, 2024, 09:52:52 am »
Please, 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 !

If I ever get that chip identified I'll make a video just for you, maybe you can learn something :D
 

Offline mikerj

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Re: LAN tester with burned IC
« Reply #9 on: May 26, 2024, 10:02:50 am »
Do you really plan to desolder SMD components on a bakelite PCB ?

Yeah, why not? Not with the hot air station of course, this should be a pretty easy job for a soldering iron :)

Please, 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 !

It 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.
 

Online daisizhou

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Re: LAN tester with burned IC
« Reply #10 on: May 26, 2024, 10:20:55 am »
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.
daisizhou#sina.com #=@
 

Offline Traceless

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Re: LAN tester with burned IC
« Reply #11 on: May 26, 2024, 10:29:14 am »
It 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.

True, 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.
 

Offline Traceless

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Re: LAN tester with burned IC
« Reply #12 on: May 26, 2024, 10:34:40 am »
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.

Yeah 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 a SN74LS90
 

Online shapirus

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Re: LAN tester with burned IC
« Reply #13 on: May 26, 2024, 10:48:01 am »
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.
 

Offline kripton2035

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Re: LAN tester with burned IC
« Reply #14 on: May 26, 2024, 10:59:17 am »
74LS90 is 16 pins ...
 

Offline Traceless

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Re: LAN tester with burned IC
« Reply #15 on: May 26, 2024, 11:03:31 am »
74LS90 is 16 pins ...

According to the Texas Instruments link i posted above it is a 14 pin IC  ;)
 

Online ArdWar

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Re: LAN tester with burned IC
« Reply #16 on: May 26, 2024, 11:04:01 am »
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.
« Last Edit: May 26, 2024, 11:07:02 am by ArdWar »
 

Offline Traceless

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Re: LAN tester with burned IC
« Reply #17 on: May 26, 2024, 12:52:54 pm »
Okay I found two sources that claim that the IC might be an "SAM8928". Here someone posted a schematic (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). On this page somone analysed and modified different version of those testers.

A quick google search did not yield any sources for that IC.

Cheers Traceless
 
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Offline Coordonnée_chromatique

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Re: LAN tester with burned IC
« Reply #18 on: May 26, 2024, 01:01:10 pm »
Please, 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 !

If I ever get that chip identified I'll make a video just for you, maybe you can learn something :D

I'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  :clap:
 

Offline madires

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Re: LAN tester with burned IC
« Reply #19 on: May 26, 2024, 01:16:18 pm »
It's quite easy with the right tool, i.e. soldering tweezers with tips for SOICs.
 

Offline magic

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Re: LAN tester with burned IC
« Reply #20 on: May 26, 2024, 01:40:14 pm »
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.
 

Offline madires

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Re: LAN tester with burned IC
« Reply #21 on: May 26, 2024, 02:27:03 pm »
Why so pessimistic? It would be a nice weekend project with a simple circuit and a bit of coding.
 

Offline amyk

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Re: LAN tester with burned IC
« Reply #22 on: May 28, 2024, 02:18:51 am »
 


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