Classe Audio CA-301, Service Manual

Page: 8 / 26

PRO-SVR_LEGACY Page 8 of 13
Output Transistors Testing and Replacement
PLEASE NOTE THAT THESE TESTS ARE ONLY EFFECTIVE ON BIPOLAR TRANSISTORS.
DO NOT PERFORM THESE TESTS ON MOSFET DEVICES, AS THEY ARE LIKELY TO
BECOME SHORT DURING THE TEST.
You should check all pin combinaisons, as there is a chance that only one side of the transistor is short. When
replacing outputs transistors, the technician should first disconnect both outputs and main board to check if
the blown outputs were caused by a faulty component on the amplifier’s base. Blown output transistors should
be replaced by kits, not individually. These kits contains matched transistors for both rails of one channel.
When replacing blown output transistors, you must also replace positive and negative Mosfet drivers and bias
transistor. Carefully inspect 4.7
ƻ resistor and 10 ƻ soft start resistor, and replace if necessary. Replace any
burnt component or board.
Pins : 1 Base
2 Emitter
Case Collector
You should have these results, if the transistor is good.
MJ21194 (NPN)
Positive lead Negative lead Result
B C Conductive
B E Conductive
C B Infinite
C E Infinite
E B Infinite
E C Infinite
MJ21193 (PNP)
Positive lead Negative lead Result
B C Infinite
B E Infinite
C B
Conductive
C E Infinite
E B
Conductive
E C Infinite