[koen.vdvelde]

Dear,

A few weeks ago I revived an older TP-Link WDR4900 using the dd-wrt firmware.

Everything went well with the exception of the 2.4GHz connection which suffered from packet loss every 2 days. A reset of the router solves this problem, but of course this is not really a solution.

Looking for a solution, I discovered that my dd-wrt firmware (version 40559, found through the Router Database) was not the most recent one. So I downloaded the most recent version from "https://download1.dd-wrt.com/dd-wrtv2/downloads/betas/2020/06-04-2020-r43334/tplink_tl-wdr4900v1/tl-wdr4900-webflash.bin" and installed it:
- factory reset via ssh "erase nvram && reboot".
- firmware upgrade via http (first time with "reset to default settings" / second attempt with "don't reset")
- wait for router reboot

After the reboot, however, my router remains in a boot-loop:
- Power LED = on
- System LED + 4x LAN LED + 1WAN LED flashing at intervals of a few seconds.

Fortunately a tftp of the 40559 build was enough to get the router working again.

Does anyone recognize this boot-loop behavior ?
Could it be that the 43334 build is not suitable for my WDR4900 router ?
Which recent firmware would work on my router ?
Any other solution would be highly appreciated ?

Thank you in advance,
Koen.

[zen1932]

At least 40559 did not work for 5GHz wireless for my
wdr4900V2.

A fix (41243) has been done, so you can try the build 41269.

is it a V2 or V1?

[koen.vdvelde]

Hello zen1932,
thanks for your information.
Mine is a v1.3. It has slightly different hardware than a v2, if I remember well.
But I'll give it a try this evening anyway ... you never know ;-)
thx,
Koen.

[koen.vdvelde]

Hello,

good and bad news.

As zen1932 suggested : I installed build r41269 on my router. This one installed fine, so I should have stopped here. Unfortunatly, too curious about finding the most recent build that would run on my router ... I continued installing new builds ...

- started from build r40559 dd 20190806 => ok
- webflash to build r41269 dd 20191010 => ok
- webflash to build r41686 dd 20191210 => ok
- webflash to build r42366 dd 20200214 => ok
- webflash to build r42910 dd 20200415 = not ok ! (boot loop with flashing lan/wan leds)
- revert with tftp r42366 dd 20200214 => ok
- webflash to build r42681 dd 20200313 = not ok ! (boot loop with flashing lan/wan leds)
- revert with tftp r42366 dd 20200214 => ok
- webflash to build r42542 dd 20200227 = not ok ! (boot stuck with only power led on and connected LAN light blinking)

And there I'm stuck :-(
As I did in previous steps, I tried to tftp-boot the last known working build r42366 dd 20200214 ... but this is not working anymore. It seems like the bootloader is no longer connecting to my tftp-server (checked with wireshark : no incomming tftp connection for 192.168.0.66).
LED Status on the router after pressing reset and turning it on :
- power LED = on
- LED of connected LAN port = blinking.

Any suggestions to bring this machine back to life ?

thanks in advance,
Koen.

[zen1932]

I am very sorry that you bricked your router.
if you do a search (4900) in this forum, you will find some tips to de-brick it.

[koen.vdvelde]

alright... I never thought I'd get this far... but since there was nothing left to lose, I threw open the router and soldered three cables for the serial connection. (pin-out etc according to : https://openwrt.org/toh/tp-link/tl-wdr4900)
Serial connection via serial-2-usb converter to my PC and connected to PuTTY (115200,8N1).
However, the result is not very promising -> see attach

I knew this router came from China, but I don't think that's a reason to talk Chinese to me yet :-(
Good news might be that it shows exactly the same nonsense on every boot.
I tried different baudrates (every possible value between 1200 and 128000bps) and with the same 8N1 setting, but only garbage kept coming out.

Am I missing something somewhere ?
- wrong pin-out
- wrong serial setting
- poor soldering
- ...

...or does my dd-wrt adventure really end here... I was just starting to like it ... :-(

K.

[zen1932]

Looking the screen shot, I can say the router is not talking Chinese to you, otherwise I would understand.

Have you tried swap TX/RX cable?

[koen.vdvelde]

LOL :-)

Thanks for the tip. I switched Tx and Rx but this results in : no data at all. So I assume my original connections were right ? ie: if Rx is connected to Rx, there is nothing to display ..

While before, Tx (router side) was probably correctly connected to Rx (computer side), so data comes in at comuter side ... but if sync settings are wrong this results in garbage displayed. So question is : what should be the correct settings ? Docu says 115200, 8N1, but this does not seem to work in my setup.

An other possibility is : my connection settings are correct, but the router is only sending garbage ...

How to find out what is happening here ?

thanks in advance for any help,
Koen.

[kernel-panic69]

Two things. Make sure the connections are solid, and if you are running PuTTY 0.73 and later, ensure this setting is checked:

Window > Translation > "Enable VT100 line drawing even in UTF-8 mode".

[zen1932]

also make sure flow control is none in putty

[koen.vdvelde]

Thanks both for your help.
I tried your suggestions (flow control & translation setting in Putty) but this did not seem to help.
I also check the soldering by connecting an osciloscoop to the serial connection of the router -> see attached screenshots. These seem to look like a clean binary stream.
I also checked the period of the pulses : I counted 87µs for 10 pulses, so this matches the setting of the Putty client (1/115200 = 8.68µs)

I also discovered that the router is reacting on input in the terminal client. When I enter some random keys and/or space/enter, a stream of nonsense-characters is displayed (see screenshot).

So I've got the feeling there is still something alive in my machine ... unfortunatly we don't speak the same language.

Any idea what I might be missing ?

Thanks in advance !
Koen.

[kernel-panic69]

Check to make sure your connections are good. All you need is TX, RX, and GND, DO NOT CONNECT Vcc. Isn't this one that you interrupt boot with "tpl", or is it one you do the reset button trick to put it into recovery mode, I forget?

[zen1932]

whaoh, I must say I admire your hardware skills.

Maybe we can now suspect the PC side, reinstall USB2TTL driver?, change USB port in PC?, use another PC?

[koen.vdvelde]

once again : thanks for your assistance !

I did some further testing this evening ...

@kernel-panic69 :
- for the serial connection, I only have 3 cables connected to the motherboard
- ref : https://openwrt.org/_detail/media/tplink/tl-wdr4900/tl-wdr4900-v1_serial.jpg?id=toh%3Atp-link%3Atl-wdr4900 : I only connected red (gnd = pin5 on DB9), blue (Rx = pin 3 on DB9) and yellow (Tx = pin 2 on DB9). There is no connection on green (Vcc)
- I already tried switching Tx and Rx, but than I don't get any output at all on Putty.
- I don't know about "tpl". Previous succesfull tftp boots were done by pressing 'reset' when turning on the router. This worked fine until the fatal r42542 build (dd 20200227).

@zen1932 :
- I don't suspect the serial cable or serial2usb convertor because I use them every now and then to connect my (win10) pc to the console port of a cisco switch, which works fine.
- But just to be sure : I connected the same hardware to a win7 portable .. with the same results.
- and to be 100% sure : I found an old WinXP pc with real serial connector and good old hyperterminal. I connected it to the serial cable direct (without the usb2serial convertor) ... but unfortunatly ... this als gave garbage-output only.

So this all is very weird :
- the scope shows a nice binary stream at 115200bps with 3.3V pulses.
- any terminal client connected with or without the serial2usb connector shows output for +/- 2 seconds, immediatly after turning on the router. But this output is un-readable
- when pressing enter, space, ... the output screen reacts with either one or some characters .. or with a continues stream of all equal characters (preferably the | symbol).

So all this looks pretty normal ... besides the fact that the binary stream is not correctly translated to readable characters. It must be something obvious I'm missing ... but what ... ???

thanks in advance for any hints ...
Koen.

[kernel-panic69]

If you connected it to a PC COM port, you may have fried it without the proper conversion cable. COM ports use 12V, the router interface uses 3.3V. There is a diagram somewhere in a wiki, on the forum, or somewhere else on the internet on how to make or procure the correct cable for RS-232.