Re: TP-Link MR3420 bricked - which version to use?

adapter must be installed also when disconnected from router wink

eventually try it on some live distro!

27 (edited by tver3305 2012-04-07 12:19:08)

Re: TP-Link MR3420 bricked - which version to use?

So I bricked my router TL MR3420 and failsafe by pressing the QSS button dint work, I had to the serial route.

I bought 2 serial to usb cables, CA-42 and CA-45. They are both clones, not the original ones, as CA-42 has a ARK3116 Chipset and CA-45 has a Prolific(PL2303, 067b:2303{Vendor Id:Product ID}) Chipset. See Pictures below.

I have tried using putty, screen, minicom and even a custom script to read data from the router, but I cant seem to get anything from the router.

Surprisingly enough, a wireless network which I set up earlier before bricking the router appears when I power on the router, but I cant connect to it!

#!/usr/bin/perl -w

# Reads data from a Current Cost device via serial port.

use strict;
use Device::SerialPort qw( :PARAM :STAT 0.07 );

my $PORT = "/dev/ttyUSB0";

my $ob = Device::SerialPort->new($PORT);
$ob->baudrate(115200);
$ob->write_settings;

open(SERIAL, "+>$PORT");
while (my $line = <SERIAL>) {
    print "$line \n";
    if ($line =~ m!<ch1><watts>0*(\d+)</watts></ch1>.*<tmpr> *([\-\d.]+)</tmpr>!) {
        my $watts = $1;
        my $temp = $2;
        print "$watts, $temp\n";
    }
}

http://i1242.photobucket.com/albums/gg523/tver3305/20120406847.jpg
http://i1242.photobucket.com/albums/gg523/tver3305/20120405842.jpg
http://i1242.photobucket.com/albums/gg523/tver3305/20120406848.jpg
http://i1242.photobucket.com/albums/gg523/tver3305/20120406849.jpg

What might be the problem? Any help is highly appreciated.

Re: TP-Link MR3420 bricked - which version to use?

@alex77

alex77 wrote:

Use a voltage meter and check the voltage between what you suspect to be GND and the other two colors. In my case the voltage between black (GND) and white was 3.2 volts DC. Between black (GND) and blue it was 0.0 volts DC. This leads to the conclusion that white means TX and hence blue means RX. You can double check, that the voltage between blue (RX) and white (TX) is also 0.0 volts DC.

Related to the ablove, my ca-45 nokia data-cable has 3 wires, white, blue and green. Voltage between White - Blue is 3.6V, between White - Green = 0V and between Green - Blue = 0v. I think Blue is ground, which kind of makes sense from your explanation. Using this combination, I get nothing from putty, even after swapping the cables a bit from here to there. Completely nothing, even no Noise.

I get some output when I touch the Tx and Rx connection though. Any thoughts?

Re: TP-Link MR3420 bricked - which version to use?

Hi tver3305!

Sorry that I did not answer earlier.
Have you already tried to shortcut the two conductors which you suspect to be Tx and Rx? This should write back your own keystrokes in putty.

I read your posts several times, but I do not have a glue what really could be wrong.

Regards,
Alex

Re: TP-Link MR3420 bricked - which version to use?

alex77 wrote:

Hi tver3305!
Have you already tried to shortcut the two conductors which you suspect to be Tx and Rx? This should write back your own keystrokes in putty.

I was utterly wrong, I suspected Blue to be my GND, but apparently my GND is White. Only when shortcutting Blue and Green does putty write My own Keystrokes to the console.

I went further and tried connecting Blue to the GND of the motherboard and Green to the Tx on the motherboard and I do get the keystrokes on putty. It seems that on my motherboard the GND and Tx are somehow connected! Should this be the case?

Re: TP-Link MR3420 bricked - which version to use?

Hi again!

Obviously you took one step further to a solution :-). In most cases GND is colorless (black; white if black is unavailable).

In my opinion it should work now, but obviously it does not. You already know that GND is white. If you would connect cable-RX to router-TX and cable-TX to router-RX it should be fine. You have only two combinations left. Just try them out:
According to your foto you should try the following combinations:
A) from left to right: pin 1 no cable; pin 2 white; pin 3 green; pin 4 blue
B) from left to right: pin 1 no cable; pin 2 white; pin 3 blue; pin 4 green

If you believe that GND and TX are somehow connected, check your soldering points once more. On the photo they look quite pretty, but maybe there are pins shortened on the back side of the router's board. So, take a look at the back side too.

Unfortunately, I have my second MR3420 borrowed to a friend, so that i cannot test with an ohmmeter the resitance between TX and GND. But you could give it a try: Unplug everything from the router and test with an ohmmeter between TX and GND. Anything above a few ohms (maybe above 5 ohms) would lead to the concludsion that they are not shortened.

I'm still curious, what the issue could be...

Regards and good luck,
Alex

Re: TP-Link MR3420 bricked - which version to use?

Hi alexx77

Finally it worked!

As we found out white is GND. I connected Blue - Rx and Green - Tx. However I could not get any output in putty.

Out of curiosity and frustration, I decided to type /rom/sbin/reboot and to my utter shock and surprise I saw the router lights flickering as if the router was rebooting!

I repeated the steps once more, ie close putty -> unplug router power -> disconnect usb -> reconnect usb -> start putty -> plug router to power. Still I did not get any output. I entered the commands

/sbin/firstboot
/rom/sbin/reboot

and the router restarted itself.

I then connected via a patch cable and everything started fine. The computer got a correct IP and I was able to access the console once again via 192.168.1.1

http://i1242.photobucket.com/albums/gg523/tver3305/20120407850.jpg

I still dont know why the putty terminal was blank!

Thanks all.

Re: TP-Link MR3420 bricked - which version to use?

Glad, you could unbrick your box at last.

Maybe some obscure putty option is set...?
The color code of your resistor looks quite correct but maybe you could check once more if it is really 10k-ohms.

Have a nice day!

Re: TP-Link MR3420 bricked - which version to use?

Hi. I have and old Celeron PC.

If i use an conventional Serial Cable with my Desktop will work the same as DKU-5 ou CA-42 cable ?

Will I need the 10k resistor with conventional serial cable too ?

Thanks

35 (edited by kicipu 2013-03-09 15:25:44)

Re: TP-Link MR3420 bricked - which version to use?

tver3305 wrote:

Finally it worked!

As we found out white is GND. I connected Blue - Rx and Green - Tx. However I could not get any output in putty.

Out of curiosity and frustration, I decided to type /rom/sbin/reboot and to my utter shock and surprise I saw the router lights flickering as if the router was rebooting!

Thank you for everyone here, I just sucessfully recovered my  bricked 3420 too.  and I just sign in to share something.

I have read this thread more than 10 times but I can not figure why my serial still give be gibberish text.. I put 10k ohm resistant between Tx-Vcc, add 20k ohm resistant between Tx-Vcc, put 10k ohm Tx-Vcc & 10k ohm RX-Vcc, take all the resistant off,  still gave me gibberish text...

I read tver3305 who typed on blank screen, also in some other thread some people also typed in gibberish console and succeded. so I tried "firstboot", "/sbin/firstboot" but not succeded.

What I want to say is...

Apparently like we all here know, but still unknown to someone who just bricked their router, that when you type "firstboot" there will be a confirmation [Y/N] question.

root# firstboot
firstboot will erase all settings and remove any installed packages. Are you sure? [N/y]

In my situation, I can not read the [Y/N] question, my serial cable console only give me gibberish text...



Note: In my case I finally manage to Failsafe and telnet to 192.168.1.1, type "firstboot", type "Y", then "reboot -f" 
(In Failsafe, I can read the [Y/N] question)
http://wiki.openwrt.org/doc/howto/generic.failsafe#in.failsafe.mode



so, for you out there who still figuring out to save your router...  good luck...

Re: TP-Link MR3420 bricked - which version to use?

aldoanizio wrote:

If i use an conventional Serial Cable with my Desktop will work the same as DKU-5 ou CA-42 cable ?

NO, you will probably fry the board.

RS232 (classic serial port) is NOT the same of 3.3V TTL serial. you need a converter, but it's simpler to get a USB to TTL serial, PL2303 based works fine, or the nokia cable..