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To troubleshoot the problem, first understand the temperature control principle of the light incubator. The incubator is controlled by the opening or closing of the electronic circuit control relay contacts to control the blouse to reach the preset temperature. Since there is no circuit diagram, it is difficult to find faults, and it is repeatedly considered to decide to find a breakthrough point from the temperature display. Open the box to check the digital display integrated circuit, there are SV DC operating voltage, there is a working voltage and the display no digital display, with experience T} 'determined to lock the suspected target fault location on the integrated block ICL7107CPL, with the new integration of the same model Blocks are replaced, and after the power is on, there are numbers on the display. Switch temperature control "measurement" block, '-97`> v" (the actual temperature inside the room at 18 °C), so that the "low" temperature is no wonder that can not wake up the "frozen" compressor. Is it the box control There is a problem with the temperature element, and the resistance value of the soldering-on temperature-control element is very close to the short-circuit. According to past experience in repairing other refrigeration equipment, it is impossible for the temperature-control element to make the compressor inoperable under such a small resistance value. Re-testing other relevant components of the line did not reveal any problems.
Is the temperature incubator temperature control element is not a negative temperature coefficient of the thermal element, but the positive temperature coefficient of the thermal element?Think of this, immediately disconnect the temperature control element, artificially increase the resistance of the two ends of the element, give The incubator is energized, the "measurement" block is set, the display shows a positive temperature number, the relay in the control line pulls in, the compressor starts up and cooling begins. Sure enough, as the analysis predicts, the temperature control element may be made of a strain gauge positive temperature coefficient resistance wire, and as the temperature increases, the resistance of the element also increases, otherwise it is low, so the control circuit is to use the positive temperature. The coefficient thermistor characteristics to control the temperature. Since the temperature control element is not readily available, the element is cleaned and dried with 99% ethanol and the resistance is restored to normal (measured at room temperature for about 1oon). The power is re-soldered and the compressed fir begins to cool. Repair to this step seems to solve the problem, but more observation for a while from the clamp meter to see that the compressor operating current is not stable, and normal (about 1A), sometimes higher than the normal value (2} 3A), especially the temperature inside the box Down to the set value, when the relay contact in the control circuit is disconnected, the compression of the heartbeat current not only does not disconnect, but instantaneously jumps to SA or above, causing the compressor protector to cause contact break protection due to the large current passing through the heat. The compressor is stopped. After the temperature in the tank is higher than the set value, the relay pulls in. The compressor protector is also reset due to the cooling contact, and the compressor starts to run unstable again. After the temperature in the tank falls to the set value, Sudden rise of the compressor winding current reappeared, and the compressor housing was hot for a while, disconnected from the compressor power line, and repeatedly turned on and off the load to observe the relay carefully and found that the contacts were slightly dithered when the relay was engaged. The suction force is not enough.There are three signal amplification circuits composed of UA741 operational amplifier integrated blocks in this control circuit.Is there a problem with the UA741?Use the same type of integrated block to replace it and try the compressor again. The start-up and running current of the machine is stable and normal, but the problem of sudden jump of the compressor winding current after the temperature in the box is cold until the set value relay contacts are opened is still unsolved, is it because there is a short circuit in the compressed Shan Europe group or the suction of the compressor crankshaft is not smooth? Causes the mechanical failure of the axis of the shaft and the shutdown measures the compressor start and running winding resistance values, respectively (normally 40S2, I0}2 or so)) o
The light incubator measured the compressor casing without leakage. With the simplest configuration dedicated circuit connected by the protector and starter, the compressor is started and operated, and the compressor operates normally, thereby eliminating the possibility of compressor malfunction. It seems to have to find problems in the control lines. Checked along the printed circuit board connection and found that the operating current for the compressor is controlled by the triac (BCRGAM). The power-off shutdown welds the thyristor to measure the resistance between the poles and is normal. Then, the resistance of other suspected components or the voltage to the ground was also found to be abnormal. Surprisingly, what causes the compressor to run out of trouble? Repeated analysis of the final suspicion may still be on the BCGGAM, will the SCR on the control board relay contacts moments due to the overload carrying the peak voltage Caused by soft breakdown, resulting in a sudden jump in the compressor winding current? It seems that only the replacement method to illustrate the problem. With the same type of triac, the problem is finally solved.
Light incubator (biochemical incubator) temperature control can be 15 `> v} 40 `1r, mainly used for animal and plant culture, reproduction and so on. The incubator suffered a lot of troubles due to long service life. The main performance is as follows: (1) The temperature digital automatic display shows only the decimal point when the power is turned on, and no other figures are displayed, so it is impossible to know the temperature inside the incubator. (2) No matter how to adjust the temperature controller, the “cooling†indicator light is off, and the compressor is not activated. The “heating†indicator light is on and the heating wire is always heated, so the temperature inside the box does not rise.