[LEDE-DEV] Fwd: TP-Link Archer C7 boot loop

[Alberto Bursi]

On 11/01/2016 08:24 AM, Jon wrote:
> Thought I'd report back.   I found out why I wasn't able to get console
> with the serial
> adapter.  Long story short,  it seems the TX line of my Archer C6 v2 has
> something like
> 500 ohms impedance to ground and to VCC!  Very strange.
>
> The RX measures about 10K both to gnd and VCC,  like you'd expect.
> Adding a 10K pull
> up won't get the TX high enough to work,  adding a 1k won't either, you
> have to go a bit
> lower than that.  An 820 ohm did the trick.  I thought I had a bad
> serial adapter, chased
> that for a while.  Even bought another C7,  a v3,  thinking the first
> was really unrecoverable,
> and that one needed a pull up as well,  but a 20K was enough pull up to
> work fine.
>
> I have no idea why that particular C7 has such low value pullups, on TX
> only...  But, I now
> have got the console, done the manual TFTP, erase, and load,  and yea
> verily... it frikin' works now.
>
> I didn't learn much about WHY loading the custom FW build caused it to
> get stuck, the same FW
> has since loaded and run.   I did use pins stuck in the holes, no
> soldered  header on the port
> the first time, so possibly there was a break in connection and the FW
> load was corrupted.
>
> Wanted to pass this along,  for those who might have a similar problem
> of not being able
> to get into the console with the serial adapter.  Measure from the
> signal pin to 3.3V and
> ground with an ohmmeter,  if it's below 1K, you need to grab a lower
> value pull up.
>

you might want to make a short article in the LEDE wiki about this 
(troubleshooting serial connections), or at least add this information 
in your device's page in the OpenWRT wiki (that will eventually be 
ported over).

Here is the LEDE wiki https://wiki.lede-project.org/start

-Alberto