Big Problem with TL-WR841ND installation

Hi, I've a big problem with TL-WR841ND !!!
In particular I've deleted for error the original firmware so I've decided to install a OpenWrt firmware by serial connection.
I've created the cable reading the instruction on OpenWrt forum: I've created a null - modem cable with this pinout:
Serial 9pin female connector --> TL-WR841ND PCB
PIN number 2 (RX) soldered to TX pin of TL-WR841ND PCB
PIN number 3 (TX) soldered to RX pin of TL-WR841ND PCB
PIN number 5 (GND) soldered to GND pin of TL-WR841ND PCB
I've also removed R26 resistor and I've soldered a 10k Ohm resistor from Tx pin to +ve pin to get correct levels.
After I've connected 9pin connector to a USB to serial adapter type Prolific PL2303 and I've started PuTTY terminal on windows operative system.
The result is a Garbled output so I cannot type the TPL password to access to.
Have you a suggest?
I await your answer.

I believe the PL2303 is an RS 232 device (+/- 12V signal)
But the modem UART is using +3.3V TTL signal.

You need need a USB to TTL adaptor.

I wish people would use the term UART to avoid confusion.