The main problem was a panel fixing bolt that caused the short circuits between power supply layers.
This burned the PCB and secondarily caused permanent short circuit between +15V/-15V/+5V layers.
Diagnosis
- The resistances between +15V, +5V, and -15V were low. The resistance between +15V and -15V is 13 Ohm.
The one between +5V and -15V is 7Ohm. And the one between +15 and +5 is 19Ohm. So the situation is
o -15V
|
+15V o-(13 Ohm)-+-(9 Ohm)-o +5V
Even after removing all of the active components from the board, they remained the same.
- The tantalum caps were removed from the board and it was confirmed that they are not the cause of the issue.
- The panel was removed from the module for the component migration to a spare board (to be described in the other entry).
I found that the screw hole and the screw have burnt marks. The screw need an insulation tube to avoid short circuit.
The other screw was also bare. The spare board has the screws with the insulation tubes.
|