@kklim 

Hello,

Please verify some basic information and we can try to fix it:

1. Is the main Deco working as a Router or an Access Point? Is the second Deco connected to the main one via wireless?

2. Try to connect your computer to the 2nd Deco M4 by an ethernet cable, then run a speedtest to test the wired connection.

3. Relocate the 2nd Deco and move it closer to the main Deco, then test the speed via speedtest again.

Good day.

@TP-Link_Deco 

1. Main deco working as router mode. second deco connected via wireless.

2. please refer to the attachment. For wired connection, at least i can get 100Mbps.

3. Tried before. nothing much improved.

@kklim 

Hello,

How about the wireless link speed on that computer or phone when connected to the 2nd Deco M4 on the ground floor? Please confirm it as below:

https://www.tp-link.com/support/faq/2265/

If the wireless link speed is slow, try with another wireless device and confirm again, tell me the model number of the wireless adapters.

Additionally, try to move the 2nd Deco M4 closer to the main Deco and ensure there are no/fewer obstacles between them. If it doesn’t make sense, reboot all the Deco units for a try.

@TP-Link_Deco 

To proof that there is no obstacles between the 2 nodes, I have removed the slave node and connected my phone to main node and below is the result 

As you can see on average at least i can get more than 100 Mbps !!

I rebooted and re-configured my slave node and below is the test result :

The slave mode performance pretty bad !!! And links speed is 175 Mbps as show below :

Please advise what else i need to test ? Or can i request a replacement unit for the faulty Deco ???? 

@kklim 

Hello, thanks for all the details.

This case will be forwarded to the engineers and they will evaluate if it needs to be replaced.

Please check your email box and they will contact you via email, thanks.