To our valued customers:
It has been brought to our attention that a certain batch of MK160 kits (Remote control via mobile phone) may show the following behaviour:
The LED responds to light/dark transitions, but the relay is not triggered.
This behaviour is related to a certain batch of LM741 op-amps.
(for the technical people: the output of the op-amp (pin 6) does not go low enough. 1.3V is required, while some don’t go below 2V).
Adding an 820 ohm resistor between the cathode of ZD2 (black stripe) and the cathode of the led (flat side) will solve the problem.
Another option is replacing the LM741 op-amp with a different type, e.g. TL071, NE5534A or even better: TLV271.
Arrangements have been made so that future productions will no longer suffer from this undesired behaviour.
Sorry for any inconvenience.