TL-WR842N Hardware Upgrade project

Hardware Questions and Recommendations
1

Hi,
I got hold of this chinese router TP-Link TL WR842N hardware version 4.1. This is a learning project. This board got 1MB flash and 8MB ram. I know it is not good enough for Openwrt.

I want to increase its flash and ram. I got all the materials required for it.

The first target is to get hold of serial debug port which seems to be deactivated.

This baord is similar to TL-WR841ND v9.0/v10.0 as shown here

There is a tip to remove R26 to activate serial debug. But after removing R26 the port is still silent.

The router board and devices attached to are shown in the images.

Sorry! I can post only one image. in one post.

IMG_20200125_150759
IMG_20200125_1507591000×1163 551 KB

Any help to get debug serial activated will be much appreciated.

Thanks

2

This is the image of flash chip and RAM.

IMG_20191220_183849
IMG_20191220_1838491500×1108 664 KB

3

And this is Processor.

IMG_20191220_183759
IMG_20191220_183759800×1242 382 KB

4

Would you post detail of serial port and cpu ..??

Which cable you have ..??

5

Sorry. I forgot upload serial port image. Please find it attached.

IMG_20200125_150825
IMG_20200125_1508251500×1282 720 KB

6

Hi,
Thanks for your response. I have uploaded the image of serial port.
This is what I have figured out. 3.3v volts can be seen trough meter when connected to 3.3v pin and GND pin.

IMG_20200125_150825
IMG_20200125_1508251500×1282 731 KB

7

CPU info is the same as in the above link. I believe it is exactly the same as V9.0.

I am using a USB TTL device to attach it to the serail port of router.

Let me know if you need more info.

Thx

8

Your circuit board not identical 841 v9/10. hardware is same.
You've soldered serial so it doesn't look very clear, maybe need to short R50.

9

OK..
put back R26 and short R50 and R32 .. or use any resistors (average 10ohm - 1k)

Which usb-ttl device ..?? .. marker or chip vendor ..?

I have good experience with PL2303 chip ..
like this: https://www.ebay.co.uk/itm/USB-to-TTL-Serial-Port-PL2303-HX-3-3V-5V-Module-Adapter-Cable-Board-500mA-UK/272758761168?hash=item3f81b066d0:g:jlUAAOSw-ldZZXbo

..it is cheap chinese clon, but working ..

10

Yup. I am also using PL2303.
As for putting back R26. This is a bit of work. And I need to buy resistors. I will let you know when I have done it.

When you say short, you mean make the connections direct. Right?
Thanks again for response.

11

Yep, connect direct two solder point at R50/R32, not need using resistor.
For safety, use multimeter to measure the continuity from RX/TX to R50/R32 to know which pins it connects to.

And remember, don't connect 3.3v pin from board to uart adapter.

12

...
forgot for R26, it is pull-up resistor ...

just try to short R50 and R32 ..
temporary with piece of wire or with tweezers
..
you can see somethink in terminal ..

1 Like
13

Sorry guys. I messed with the board. I think the soldering gun was too hot for these delicate connections on the board. The copper connentions came off the board and now I can't short the connections.

I am very grateful to you for your kind help. I got another Tenda F3 modem but it power connector is different. I have ordered power connector and as it arrives I will let you and ask for help.