Comark RF500A/AP Service Manual
Tier 3: RF500A Component Level Repair
Fault Finding
Before any component level fault finding the following should be checked for:
•
Missing Components
•
Lifted Pins
•
Dry Joints
•
Solder Shorts
•
Ensure inter-connecting tracks reach their destination
MPU
Common faults resulting in the MPU not functioning are:
•
Check power connections
•
Check X421 are connected
•
Ensure inter-connecting tracks reach their destination
•
Replace U421
Serial Communications
If there is no comms to the board check U421
USB Communications
If there is no comms to the board check U541.
5V Rail
If the 5V rail is inoperative of out of specification, common items to check would be:
•
Check supply to U341
•
Check shutdown pin of U341
•
Check the correct values are fitted for R341 and R342
•
Check Q341 (this is the over voltage protection)
•
Ensure inter-connecting tracks reach their destination
3VM Rail
If the 3VM rail is inoperative of out of specification, common items to check would be:
•
Check supply to U362
•
Ensure inter-connecting tracks reach their destination
•
Replace U362
17 November 2011
Page 46 of 65