APC BX700U UPS not working and beeping when plugged in - Repair of SMD components
Had this UPS in, we normally don't do these but it was from a former coworker and friend of our boss. It's a cheapo little APC UPS.
The UPS would beep continuously when plugged in and would not deliver any power. New battery was fitted and it did not solve the problem. Actually, the UPS ran fine on the battery alone, but cut the power and kept beeping when it was plugged in.
Upon investigation, the large relay that was meant to couple 230V AC mains into the rest of the unit was not switching. Therefore, the battery was not charging, either. I had checked for shorts so i strapped the relay for a test - the UPS started charging the battery.
Checked the relay coil voltage and it was 7 volts, on a 12 volt relay. So it was supposed to be turning on but there was not enough voltage on the coil to switch it. The issue was caused by one of the diodes in the double diode D11 and transistor Q23 being (partially) open. Replacement of both components solved the problem. This is shown in more detail in the attached photos.
The UPS would beep continuously when plugged in and would not deliver any power. New battery was fitted and it did not solve the problem. Actually, the UPS ran fine on the battery alone, but cut the power and kept beeping when it was plugged in.
Upon investigation, the large relay that was meant to couple 230V AC mains into the rest of the unit was not switching. Therefore, the battery was not charging, either. I had checked for shorts so i strapped the relay for a test - the UPS started charging the battery.
Checked the relay coil voltage and it was 7 volts, on a 12 volt relay. So it was supposed to be turning on but there was not enough voltage on the coil to switch it. The issue was caused by one of the diodes in the double diode D11 and transistor Q23 being (partially) open. Replacement of both components solved the problem. This is shown in more detail in the attached photos.
Attached Files
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