[SOLVED] I need a favour (WNR834B JTAG)

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spookyghost
DD-WRT Novice


Joined: 28 Oct 2009
Posts: 6

PostPosted: Wed Oct 28, 2009 17:00    Post subject: [SOLVED] I need a favour (WNR834B JTAG) Reply with quote
Hello everybody,

I'm desperate to fix my NetGear WNR834Bv2 router. Something went wrong while installing DD-WRT (after switching from Xwrt) and now I have a bricked router.

The routers MAC address got corrupt and I have no solution to fix this. The strange thing is, the router keeps starting in TFTP mode (TTL=100) by default! The router accepts a new firmware but either ignores the after a successful transfer or crashes. I tried sending a .CHK firmware and a .BIN (I believe the .BIN makes it crash; ie lights turn off, except the power LED or cable LED).

I tried pinshorting after so many TFTP retries which didn't work for me. I'm familiar with this method as I revived a WRT54G twice using this unorthodox method.

Since I'm electronics illiterate I'm basically forced to ask you guys if anybody can provide me one. I tried searching around on Google, eBay, etc but all I found was WRT54xx JTAG cables.

How much does it cost to create a JTAG cable? Are there other solutions (serial cable?)

Please help :(

edit: possible helpful links

Installation guide from the wiki contains pin layout
Userguide unbricking WNR834Bv2 containing an image with JTAG pins


SOLVED:

Finally after 2 days of JTAG'ing I brought my router back to life. I had a slow start because of JTAG cable problems. To anyone who buys a JTAG cable off eBay (or anywhere else), be sure to buy at least buy one 100 ohm resistor. You need this to connect the J12 pin 1 to JP1 pin 1.

I used the steps explain in this topic.

Since I had problems getting the flash chip detected, I power cycled the router many times and literally SPAMMED the tjtag commands to get it working. Also, after power cycling (as explained in the other topic) gave me problems and commands kept crashing all the time. Pressing Ctrl+C and spamming the same command did the trick. Sure it crashed often but I didn't care... Ctrl+C, and retry until it works.

After powercycling to TFTP the, I used the European bin file. The router stopped responding to pings but I left it running for at least 5 minutes. This didn't help at all, so I power cycled again. Then I retried TFTP'ing the American firmware.. waited for yet another 5 minutes. I never got a ping (TTL=64) reply back until I power cycled after those 5 minutes.

Since the American firmware is an older version, I downloaded the (original) European firmware and uploaded it using the webinterface. Worked like a charm.

*does a victory dance*


Last edited by spookyghost on Sun Nov 22, 2009 19:20; edited 2 times in total
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beyondwind
DD-WRT Novice


Joined: 27 Oct 2009
Posts: 19

PostPosted: Thu Oct 29, 2009 2:11    Post subject: Re: I need a favour (WNR834B JTAG) Reply with quote
spookyghost wrote:
Hello everybody,

I'm desperate to fix my NetGear WNR834Bv2 router. Something went wrong while installing DD-WRT (after switching from Xwrt) and now I have a bricked router.

The routers MAC address got corrupt and I have no solution to fix this. The strange thing is, the router keeps starting in TFTP mode (TTL=100) by default! The router accepts a new firmware but either ignores the after a successful transfer or crashes. I tried sending a .CHK firmware and a .BIN (I believe the .BIN makes it crash; ie lights turn off, except the power LED or cable LED).

I tried pinshorting after so many TFTP retries which didn't work for me. I'm familiar with this method as I revived a WRT54G twice using this unorthodox method.

Since I'm electronics illiterate I'm basically forced to ask you guys if anybody can provide me one. I tried searching around on Google, eBay, etc but all I found was WRT54xx JTAG cables.

How much does it cost to create a JTAG cable? Are there other solutions (serial cable?)

Please help :(



edit: possible helpful links

Installation guide from the wiki contains pin layout
Userguide unbricking WNR834Bv2 containing an image with JTAG pins


the wnr834bv2 pinout is the same as wrt54, plus most adapters you buy from ebay will have pogo pins with which you can make your own pin arrangement.
spookyghost
DD-WRT Novice


Joined: 28 Oct 2009
Posts: 6

PostPosted: Thu Oct 29, 2009 7:09    Post subject: Re: I need a favour (WNR834B JTAG) Reply with quote
beyondwind wrote:
the wnr834bv2 pinout is the same as wrt54, plus most adapters you buy from ebay will have pogo pins with which you can make your own pin arrangement.


Sweet! I didn't know that. I'm getting my hopes up here Very Happy Soooo I did a quick search on eBay. I couldn't find anything within Europe (preferably The Netherlands) but I found this JTAG cable from the US. It looks really good from what I can tell, plus it comes with pogo pins (like you mentioned) .. I was hoping to not have to solder, but I don't see a header thing on the picture from the other thread (2nd link). I'll have to recheck my own router this afternoon to be sure.

Can someone back this up? Or has experience buying cables/anything from eBay (never used eBay before; not sure about safety whatsoever)
spookyghost
DD-WRT Novice


Joined: 28 Oct 2009
Posts: 6

PostPosted: Sat Oct 31, 2009 20:00    Post subject: Reply with quote
I'm waiting for my PayPal account to get verified. I have to wait 2-3 days, expecting to have it verified by Tuesday. Then I can order the cable .. shipping is within 24 hours so hopefully I'll have it on Friday probably. I can hardly wait to fix my router Very Happy
tenho
DD-WRT Novice


Joined: 16 Mar 2009
Posts: 16

PostPosted: Sat Nov 21, 2009 12:46    Post subject: Reply with quote
So any progress on this topic? The JTAG cable came already? I have also interest on debrickung a WNR834B with JTAG.

Cheerz
spookyghost
DD-WRT Novice


Joined: 28 Oct 2009
Posts: 6

PostPosted: Sat Nov 21, 2009 20:14    Post subject: Reply with quote
tenho wrote:
So any progress on this topic? The JTAG cable came already? I have also interest on debrickung a WNR834B with JTAG.

Cheerz


No progress so far. I'm trying to JTAG at this very moment but I'm not having any luck getting it probed.

I keep getting the next response from the JTAG tool:

====================================================
Probing bus ... Done

Instruction Length set to 5

CPU Chip ID: 00000000000000000000000000000000 (00000000)
*** Unknown or NO CPU Chip ID Detected ***

*** Possible Causes:
1) Device is not Connected.
2) Device is not Powered On.
3) Improper JTAG Cable.
4) Unrecognized CPU Chip ID.
====================================================

I can think of 2 possible reasons:
- I did a poor job soldering the pins on the router
- I'm not correctly plugging the header cables (that came with the LPT cable that I ordered on eBay) on the router


I'll post an update when I get more out of this piece of .... brick.
spookyghost
DD-WRT Novice


Joined: 28 Oct 2009
Posts: 6

PostPosted: Sat Nov 21, 2009 21:23    Post subject: Reply with quote
I checked all the cables with a multimeter and they seem fine (from proper LPT pins all the way to the end). But still no CPU chip ID.

Am I missing something here? Do I need to start the router in a "special" mode?

*sigh*
spookyghost
DD-WRT Novice


Joined: 28 Oct 2009
Posts: 6

PostPosted: Sun Nov 22, 2009 15:52    Post subject: Reply with quote
well I got something working now. I can JTAG it now and use the JTAG tool. The reason I couldn't before, is because I had to connect one cable differently. (J12 pin 1 to JP1 pin 1 via 100ohm resistor). I thought the cable I bought did this internally (not sure why I thought that) so I got myself a 100ohm resister, connected these 2 pins and viola!! JTAG works.

Now it's trying to probe the flash chip after using the command: tjtag -flash:cfe /noemw /noreset

It's taking a very long time and I suspect it hung.

Wish me luck.
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