Experience in repairing injection molding machine malfunctions

To repair a relatively unfamiliar injection molding machine circuit board without any schematic diagram, the so-called "experience" in the past is difficult to achieve. Although people with strong hardware skills have confidence in the repair, if the method is not appropriate, the work will still be twice the result with half the effort. So, how can we improve maintenance efficiency?
Tools used: multimeter, magnifying glass
When holding a circuit board for an injection molding machine to be repaired, a good habit is to first visually inspect it, and if necessary, use a magnifying glass to see what?
Mainly looking at:
1. Is there any wire breakage;
2. Discrete components such as resistance, electrolytic capacitor, inductance, diode, triode, etc. are disconnected;
3. Check if the printed circuit board connecting wires on the injection molding machine circuit board are broken, adhered, etc;
4. Has anyone repaired it? Which components have been touched? Whether there are errors in operation such as false soldering, missing soldering, and reverse insertion;
After confirming that the repaired part does not have the above conditions, first use a multimeter to measure the resistance value between the power supply and ground of the injection molding machine circuit board. If the resistance value is too small, only a few or more ohms, it indicates that there are components on the injection molding machine circuit board that have been broken or partially broken, and measures must be taken to find the broken components. The specific method is to supply power to the repaired circuit board and touch the temperature of various components on the injection molding machine circuit board with your hand. Those who are hot will be the key suspects. If the resistance value is normal, use a multimeter to measure the resistance, diode, transistor, field-effect transistor, dial switch, and other vertical components on the board. The purpose is to first ensure that the measured components are normal. Our reason is that the problem that can be solved with a multimeter should not be complicated.