Automatic hand dryer faults and troubleshooting

Infrared automatic hand dryer, widely used in hotels, hospitals, restaurants, bathrooms and other public places. For the convenience of maintenance dissected the machine circuit, draw the circuit diagram (see attached). And introduce the common causes of failure and simple processing, for reference.

I. Circuit principle
Circuit by V1, V2, R1, C3 constitute a 40kHz oscillator, its output drive infrared tube D6 issued 40kHz of infrared light. When the hand reaches below the hand dryer, the infrared light reflected by the hand is received by the photoelectric tube D5. It is converted into a half-wave pulsating DC signal. The signal is coupled by C4 to the first level op-amp positive input for amplification, the negative end to add a small bias voltage to prevent small signal interference. The amplified signal is output from pin ① to R7, D7 and C5 for shaping and smoothing into a DC signal. The signal is sent to the positive input of the second stage op-amp at pin ⑤ for comparison and amplification. R10 is the positive feedback resistor of the op-amp, and C5 and C6 together form a delay circuit to prevent the hand being detected from moving. The interference generated by the power failure phenomenon. When the op-amp (7) pin output high level V3 conductive. Control relay to turn on the power of the heater and hair dryer.

Second, the common causes of failure and elimination
Fault 1: the light is on after the power is turned on. But no hot air blowing out after reaching.
Analysis of the fan and the heater at the same time the possibility of failure is very small, mostly seen as a bad relay or not action, and J not action may be V3 not conductive; op-amp no output; D6, D5 failure; V1, V2 not start or 7812 damage resulting in no 12V voltage.
When checking, first measure whether there is 12V, if there is, reach out and test the op-amp (7) pin level change. If there is a change, check V3 and relay backwards; if there is no change, check the op-amp circuit, photoelectric conversion and oscillation circuit forward.
Fault 2: After power on the light is on. But the induction sensitivity is low.
This fault in addition to the op-amp circuit has abnormalities, mostly seen for the red launch and receive tube is dust pollution caused by. Cleaning can be.