Service manual

Troubleshooting 41
Note Because test points on the FET board are not accessible when the board is installed, troubleshooting must
be performed with the board removed from the power supply (refer to the disassembly procedures at the
back of this chapter
If any power FET (Q201-204, Q301-304, Q211, Q311, Q222, Q322, Q233, Q333, Q244, Q344) is
defective, you must replace all eight with a matched set.
TURN OFF SUPPLY AND REMOVE
A3 FET BOARD WITH HEATSINK
MEASURE RESISTANCE BETWEEN
+RAIL AND -RAIL (E201 AND E301)
>=20 Mohm?
>15 Kohms?
CONTINUE WITH DYNAMIC
YES
YES
YES
NO
NO
NO
(SEE DISASSEMBLY PROCEDURES)
PROBABLE DEFECTIVE
A3 BOARD
MEASURE RESISTANCE BETWEEN
THE GATE OF EACH FET AND
COMMON (-RAIL)
MEASURE RESISTANCE ACROSS
CAPACITOR C201 AND C301.
approx.
150 ohms?
YES
NO
MEASURE RESISTANCE ACROSS
15V BIAS INPUT.
1k ohm forward?
490 ohm reverse?
TROUBLESHOOTING IN TABLE 6-3.
NOTE:
BECAUSE TEST POINTS ON THE A3 FET BOARD ARE NOT
ACCESSIBLE WHEN THE BOARD IS INSTALLED, TROUBLESHOOTING
MUST BE PERFORMED WITH THE BOARD REMOVED FROM THE SUPPLY.
ASSEMBLY ATTACHED.
PROBABLE DEFECTIVE
A3 BOARD
PROBABLE DEFECTIVE
A3 BOARD
PROBABLE DEFECTIVE
A3 BOARD
(E206 TO E207 AND E306 TO E307)
Figure 3-11. FET Troubleshooting Chart)