Tuesday, February 07, 2017

Classe CAM 350 – Mono Block Power amplifier – Protection mode – Troubleshooting – How to check output transistor – Idle current adjustments

Protection and Indicators Modes 
The front LED shows the status of the amplifier. When starting up normally, the CAM350 will show a FLASHING RED LED for about 15 seconds and if all is normal, the LED will go SOLID RED. If there is a fault, the LED will go to a FLASHING GREEN LED. The CAM350 is equipped with four Mosfet protection fuses. In the event that one or more of these fuses would blow, first need to identify and cure the cause of failure. When the cause has been identified, disconnect the unit from the system including the AC power. Remove the top cover and look for damaged or burned components. If no other components than the fuses appear to be damaged,  then replace the broken fuses with the same value and rating. The Mosfet fuses are located on the control board. When replacing fuses, make sure that the fuse holder are holding the fuses very tightly. A loose fuse holder can translate into distortion on top of the signal.
Troubleshooting
Symptom
Possible cause
Unit won’t turn on
Check connections;
Check fuses;
Check soft-start circuit;
Check relays;
Check power supply circuits (positive rail, negative rail, Mosfet supply).
Smoked and/or burned
components
Check for short between components and ground;
Check output transistors;
Check output relays;
Check power supply circuits (positive rail,   negative rail, Mosfet supply).
Blown fuses
Check for short between fuse and ground;
Check power supply circuits (positive rail, negative rail, Mosfet supply).
No output
Check connections;
Check output relays;
Check power supply circuits (positive rail, negative rail, Mosfet supply);
Check output transistors.
Unit turn into protection
Check for smoked and/or burned components;
Check power supply circuits (positive rail, negative rail, Mosfet supply);
Check source and load;
Check protection circuit;
Check sensor wires between sensor PCB and control PCB;
Check outputs transistors and Mosfet drivers.
Excessive buzz and/or hum
Check electrical lines;
Check for a ground loop in the system.
Oscillation
Check source;
Check capacitors on main board;
Check 4.7 Ohms resistor.
Intermittent signal
Check connections;
Replace shield wires.
How to test the output power transistor 
Pins :
1 Base
2 Collector
3 Emitter
You should have these results, if the transistor is good.
2SC3264 (NPN)
Positive lead
Negative lead
Result
B
C
Conductive
B
E
Conductive
C
B
Infinite
C
E
Infinite
E
B
Infinite
E
C
Infinite
2SA1295 (PNP)
Positive lead
Negative lead
Result
B
C
Infinite
B
E
Infinite
C
B
Conductive
C
E
Infinite
E
B
Conductive
E
C
Infinite
Calibrations and Adjustments
Bias adjustment:
Note: Bias adjustment should be made without any load connected to the amplifier’s output, and no signal connected to the amplifier’s input.
1. On positive rail, connect a multimeter to R111 leads and set the multimeter to mV scale.
2. Turn trimpot R104 counterclockwise until it reaches 0 Ohm. A click should be heard.
3. Turn on amplifier, and let it warm up for 15 minutes on idle.
4. Adjust trimpot R104 to get a 10mV reading.
5. Repeat procedure with negative rail.
6. Let the amplifier warm up for a 24 hours period with signal and load.
7. Remove signal and load, and reconnect the multimeter, setted to mV scale, to R112 leads.
8. Readjust R104 to get a 12mV reading.
DC offset:
Note: DC offset adjustment should be made without any load connected to the amplifier’s output, and no  signal connected to the amplifier’s input.
On these units, DC offset can’t be adjusted. Measure DC offset using a voltmeter connected to the output posts, scale setted to mV. DC offset should be less than 10mV.