We have purchased many of the MK162 transmitters but now have quite a few that do not work. All batteries are new or nearly new but we have found that if we fit a new chip to them then they start working again? (chip ref 12f629 - i/p4mb - 0807 )
Why is this? and if we need new chips where do we get them from? however we would rather do a repair if you can suggest anything.
It is highly unlikely that the processors are defective, unless there is an assembly mistake on the MK162 board.
Most likely, the address of the unit has been changed, so that the receiver no longer responds. Please check this.
I am having the same problem.
I have 2 units. One of the ICs works in both units and one of the ICs doesn’t work in either unit.
Could you please elaborate on how to correctly set the address?
Are you referring to changing the channel by holding down both switches until the leds flash in one second intervals? I have tried this and it does not help my situation.
Are there off the shelf replacement chips? Or do these generic chips need to be programmed in order to function in this circuit?
Thanks for your help!!
Problem solved!! 
I was thrown off by the name of the kit “2-Channel IR Transmitter” forgetting that the unit can be programmed for any of 16 channels. I used a different case and wired up one of the switches to a panel mounted illuminated switch (keeping the second switch on the pcb for programming), so I forgot that the second switch can transmit on a different channel, making it a 2-simultaneous channel transmitter.
I found the best way to set the channel/address is to aim the transmitter at the receiver and hold both switches down and let the unit scroll through the channels until the receiver reacts, then let go and the unit is then set to the correct channel.
Hope this helps anybody else with this problem.