Did you actually measure the voltage?
If you're using a laptop to make the connection, try running on battery only.
I'd also try another USB port if you have one.
No, I didn't measure it, i do not have a multimeter. I was on PC using usb 2.0 port.
I'd also try another USB port if you have one.
But cable worked on different router, and i captured the u-boot logs from it.
U-Boot 1.1.4 (Apr 13 2013 - 16:23:22)
AP91 (ar7240) U-boot
DRAM:
sri
#### TAP VALUE 1 = 9, 2 = a
32 MB
id read 0x100000ff
flash size 4194304, sector count = 64
Flash: 4 MB
Using default environment
In: serial
Out: serial
Err: serial
Net: ag7240_enet_initialize...
No valid address in Flash. Using fixed address
: cfg1 0xf cfg2 0x7014
eth0: 00:03:7f:09:0b:ad
eth0 up
No valid address in Flash. Using fixed address
: cfg1 0xf cfg2 0x7214
eth1: 00:03:7f:09:0b:ad
ATHRS26: resetting s26
ATHRS26: s26 reset done
eth1 up
eth0, eth1
Autobooting in 1 seconds
## Booting image at 9f020000 ...
Uncompressing Kernel Image ... OK
Same USB port?
Picocom on both routers?
Yes, and same pinout.
Picocom on both routers?
Yes, and on wdr3500 i`ve tried screen also with all bauds you mentioned.
Just noticed there are actually 4 pinouts on the screenshot of the board with the pins identified...the 4th doesn't have a pin inserted. That's the 3.3V, which you don't want to use.
Looks like pogo pins in GRND, TX and RX in the screenshot.
So, sticking with the pins identified in the screenshot, you've tried -
GRND to GRND
TX to RX
RX to TX
GRND to GRND
TX to TX
RX to RX
It's possible something got fried during soldering, if too much heat was applied.
I personally don't solder.
yes
At first i did not solder, just pressing with my fingers, while trying different combinations, nothing worked anyway.
Hopefully beeweezer will have another shot at this 
Hmm, if i think about it, while trying what slh suggested
Konsole did spit some artifacts while router was booting, but not much.
Router is off when you're making the connections, then turned on?
Yes, of course.
Since we can't see what you're doing, asking is better than assuming.
Are you using a laptop running on AC power, or battery?
I`m using a Desktop PC running on AC power 220v
Has the WDR3500 ever been successfully flashed via serial before?
No, only with SSH, are you asking in general, or in my case specifically?
Asking if serial has ever worked on your WDR3500.
In 99.99% of all cases, the way the computer/ notebook is powered doesn't make a difference for this, chances are much higher that the fake ca-42 cable which should be using 3.3V is actually 5V based, messing up the tripping points for HIGH/ LOW and also bothering the ar9344 SOC (by backfeeding 5V into the SOCs rx line).
Unless that can be ruled out (by measuring the voltage between rx and tx against GND, which should be slightly below 3.3V at most), it's not going to work with this cable - and trying further might have adverse effects on the router hardware (which really doesn't like to see 5V).
No, this is the first time im trying serial on that router.
1 Like
That makes sense, except that the CA-42 works fine with the other router.
Tolerances…
For what it's worth, if I could, I would send you a USB to TTL UART, and some pogo pins so you wouldn't have to solder.
Thanks for hanging in with us.
Stay safe...thoughts and prayers for you, your family, and the citizens of Ukraine.
Thank you <3
But im not going anywhere yet XD, i love staying here. Im thinking about buying a proper serial dongle and taking a shot at this again.
And we don't want you to leave..
Appreciate your willingness to answer questions, and try out what's suggested.