Centralion 400VA - Battery Mode Troubleshooting; MOSFET and CPU Checks; Power Supply and Component Testing

2.1 Battery mode examination (please refer flowchart)
Procedure :
1 .(1) Replace batteries by DC power supply and turn on it.
(2)Check if there is current limit phenomenon for DC power supply.
2 One or more MOSFETs (Q20,Q23~25) is D-S short. Check and replace it. If
MOSFETs have been replaced once, replace the PCB.
3.
Check if both buzzer beeps and LED flash for once.
1.
Check if +5V on CPU pin 25 is normal.
2.
Check if clock signals on CPU pin 22 and 23 are correct.
3.
Replace the CPU. But if the CPU has been replaced once, replace the PCB.
4.
Replace abnormal crystal XL1.
5.
Check if DC fuse F01 (and F02) are open.
6.
Replace abnormal DC fuse.
7.
Check if there is a battery voltage on regulator 7805 input.
8.
Check Q11 (MPS2907A) ,Q12(2222ASM) and replace them if abnormal.
9.
Check there is +12V on 7805 input.
10.
Replace abnormal Q11.
11.
Check there is +5V on U03 (7805)
12.
Replace abnormal 7805.
13.
Replace PCB
14.
Check if buzzer beeps and LED extinguished.
15.
Check if battery voltage is correct.
16.
Replace abnormal batteries.
17.
Check D17 if it is open.
18.
Replace abnormal Diode.
19.
Replace PCB.
20.
Buzzer beeps and LEDs flash .
21.
Check if fault LED lights and buzzer beeps continuously.
22.
Check if CPU is shorted.
23.
Replace abnormal CPU.
24.
Check if Q22 (RFP50N06) is shorted.
25.
Replace abnormal RFP50N06.
26.
Check if Q07 is failed.
27.
Replace abnormal Q07.
28.
Replace PCB.
29