Electrical Repair is No Longer Solved by a Multimeter Alone

Today, I repaired a batch of servo drivers. When powered on, I measured various voltages and found no output, with some issues appearing intermittently. The chip used is the UC2842, and the supply voltage was alarmingly low. I measured the startup resistor, supply capacitor, and supply diode, all of which were normal, leading me to suspect a chip failure. After replacing it with a new chip, the fault persisted. I then found another chip and tested it externally with DC, which worked fine. After installation, the fault remained. I took many detours, and here I will skip the details~~~~~ Finally, feeling helpless, I used an LCR meter to recheck the power supply section, which was my main suspicion, and the problem finally surfaced. The ESR of the power supply electrolytic capacitor and the output supply capacitor was high (the capacitance measured normal with a multimeter).

This ultimately led to low output voltage, causing intermittent operation or power loss during operation. Many capacitors were located very close to the heat sink, which likely caused them to be damaged.

After replacing with new capacitors, I analyzed: we generally habitually use the capacitance measurement function of a multimeter to measure capacitors, and rarely use an LCR meter, or some repair technicians may not even have one. After this experience, we repair personnel should use LCR meters more often to measure various components, as it is more reliable. If you don’t have one, you can buy a DIY LCR meter from online stores, which is also quite good. I use a meter from Teacher Xu, which is generally sufficient for repairs. This is not an advertisement; I just feel that we need to equip ourselves with LCR meters, oscilloscopes, and other devices for future electrical repairs. Relying solely on a multimeter and experience is no longer sufficient. It is also not just about replacing components blindly. Many times, precise measurements with instruments are necessary to accurately determine the source of the problem. Otherwise, even if you fix it, you won’t know which component caused the fault.

Original text: https://www.jdwx.info/thread-798941-1-1.html

Home Appliance Repair Forumjdwxinfo▲ Long press to recognize the QR code to follow

Home Appliance Repair Technology Forumjdwx-cn▲ Long press to recognize the QR code to follow