Hi all,
As shown in the figure, the two resistors R125 and R124 are missing, causing the inability to input commands. One chip circuit is grounded (r125), and the other is connected to the ttl socket (r124).
Can anyone help me?
How ?
Want someone to fax you new resistors?
Oh of course not, I want to know the resistance data of these two resistors
10K is always a good start for basic pull up's or pull downs
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Do both use 10k? I will give it a try 
This is a guess, I don't know what they do in this circuit
but if they are pull-ups or pull downs, 10K is common
but only if the voltage rails are the same as the TTL voltages
you normally need 1 pull-up on the RX line into the chip
the TX out of the chip should be ok without
maybe a in line short protection resister but uncommon
if they are voltage dividers, could be anything
Okay, maybe I should try measuring the resistance in the TTL circuit on other routers to verify? I don't know if this will help me, but it's okay to give it a try
This is what I would do
presuming the pads there are the TTL serial interface
with the router powered on
check the pads GND and VCC
make sure there are the expected voltage V3.3
then measure GND and the TX out pin
it's driven, so should be close to 0 or V3.3 I think high so ~V3.2
then the RX input pin should be floating but pulled up so V3.0 to V3.1
with USB powered serial devices, you only need GND TX and RX
so connect RX to TX and make sure it echoes data in a console
then as these names get mixed up RX and TX
you need to make sure
input is connected to output and
output is connected to input
Thank you for the information, I will try it.
I have this router working as my main router right now