New function added to MF-47D multimeter - infrared remote control detection

The MF-47D multimeter retains all the measurement functions of the original MF-47 and adds new functions such as infrared remote control detection, circuit buzzer prompt, and super-β transistor measurement.

The infrared remote control detection circuit is made on a 2.2×1.4cm circuit board. See the attached figure for the circuit. The infrared remote control detection circuit receiving part does not use an integrated micro remote control receiving head, but uses a φ3 black infrared receiving diode, which is smaller in size.

The circuit uses a 9V power supply directly, eliminating the trouble of using the 5V power supply required by the integrated micro remote control receiver. Two diodes are exposed at the lower left of the dial, and a graphic logo is marked next to the receiving diode.

When testing the infrared transmitter, turn the gear switch to R×10k, align the transmitter head vertically with the receiving window within ±15 degrees, press the function key to be tested, and the red light-emitting tube flashes when it works normally. Move the transmitter within a certain distance (0-10cm) to determine the transmitter output power status. If enthusiasts imitate this circuit, they can add a switch to the multimeter housing, and the circuit board can be properly placed according to the space inside the meter.

I was repairing a meter of this type for a colleague and found that the resistance block of the meter was malfunctioning. I found that the resistance of the resistance block R×1~R×1k block was burnt out and was unrecognizable. I replaced the resistance according to the circuit diagram provided by the manufacturer with the meter. The resistance of R×1, R×10, and R×100 blocks were marked as 15kΩ, 165kΩ, and 178kΩ, respectively, which was obviously wrong. Generally, the resistance of the ×1 block of a multimeter is about 10Ω. After trying to replace the resistance of R×1 block with 15Ω, the test was normal. Then the marking of R×10 and ×100 blocks must be wrong, and should be 165Ω and 1.78kΩ respectively. After the replacement, it was proved that the judgment was correct.

There is another error in the random circuit schematic diagram of this table, that is, the DCV1, ACV1, Ω and + jacks in the original diagram are not connected, so the circuit cannot work and the connecting lines should be added.