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Failed TP-Link Kasa Smart KP115 WiFi Plug with energy monitoring relay replacement

Repairing a Failed TP-Link Kasa Smart KP115 WiFi Plug which has a dead relay

For the past few months, I have been using a TP-Link Kasa Smart KP115 WiFi Plug with energy monitoring to control the mains power for my Samsung TV and Sony soundbar and sub-woofer.

I only watch a couple of hours TV every day so for over 22 hours each day the TV and soundbar are on standby.

To reduce the power consumption when the TV is not being used, I was using the TP-Link Kasa Smart plug to turn off the mains supply when it is not in use and the smart plug also disconnects the power after 5 minutes of the TV and soundbar being on standby.

In the past few weeks, the smart plug was showing as being turned off but the mains power was still being supplied to the TV and soundbar. The internal relay was sticking closed and could only be released by banging the side of the smart plug which would fix it for a few days and then it would stick again.

This is the third smart plug which has failed when connected to the TV and soundbar, the previous two models where Samsung Smart Plug GP-WOU019BBDWG which are completely sealed but the TP-Link KP115 has a small gap in the plastic case which indicated it would be possible to remove the cover to repair it.

TP-Link Kasa Smart KP115
TP-Link Kasa Smart KP115 WiFi Plug with energy monitoring

To remove the cover first you need to use a thin flat blade to insert into the gap in the case and working around the edge gently prise the cover away from the plug pin side. The cover is held in place with several small plastic clips around the base and once these have been released the cover will lift away.

Cover and PCB removed
Cover and PCB removed

Inside is the main printed circuit board with the live and neutral sockets and the relay on the right side.

Below the relay and earth connection are a pair of diagonal pins which are the mains input for the board. These need to be heated with a soldering iron to remove the PCB from the case.

PCB Top with relay removed
PCB Top with relay removed

Once with the board has been removed, this will reveal the bottom of the board which has a small foam block across the relay contacts which appears to be insulation across the mains voltage contacts.

Removing the foam pad allow access to the relays pins and this was removed with the desoldering iron to clear the holes.

PCB Base
PCB Base

With the relay removed, I was able to find the model number which is a Churod Electronics | A16-V-112DA2F,000. This is a SPST relay with a 12-volt coil. The contacts are rated at 16 Amps which is much higher than the current consumption of the TV and soundbar when in use.

The Churod relays only appear to be sold in quantities of 100 from China and so I looked for an alternative model. The TE Connectivity, 5V dc Coil Relay SPNO, 16A Switching Current PCB Mount Single Pole, 1-2071556-2 closely matched the specifications and I ordered a replacement from RS Components. The new relay cost £2.09 for a pack of two so I now have a spare relay.

Old Relay removed
Old Relay removed
Old Relay removed
Old Relay removed
Relay contacts
Relay contacts
Old Relay Contacts Damage
Old Relay Contacts Damage

The new relay was soldered to the board and the PCB was soldered back onto the mains supply pins.

New relay installed
New relay installed

The cover was clipped back to the base and tested to ensure the new relay is now working as expected

Assembled and ready to use again
Assembled and ready to use again

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