Crossfire CFA602

[mike49504]

This amp wont power up heres the voltages on the 494

1:0
2:4.93
3:.05
4:4.93
5:1.43
6:3.59
7:0
8:13.93
9:0
10:0
11:13.93
12:13.93
13:4.92
14:4.93
15:4.93
16:0

 

[Perry Babin]

Have you replaced any components?

Have you checked the outputs?

 

[mike49504]

Havent repalced anything yet . Outputs test fine in the board i havent taken them out to check for leakage yet. Power light comes on for a sec then shuts right off

 

[Perry Babin]

Pin 4 is being driven high. Follow the circuit back to see if you can find what's driving it.

 

[mike49504]

I see a Transistor A1266 that goes to pin 4 I will test that and see what i come up with.

 

[mike49504]

After the transistor it goes back to a thermistor. Which measures 4.95k across it. Do i need to follow the circuit back more?

 

[Perry Babin]

Is the emitter of the 1266 connected to pin 14 of the 494?

If so, remove it to see if it will power up but be prepared to shut it down if the amp begins to draw excessive current.

 

[mike49504]

With the A1266 removed amp powers on and idles perfectly and also produces audio.

 

[Perry Babin]

Does the base of the 1266 connect to a transistor in the audio section (near Q130, 131, 132, 232)?

There may be a resistor in series between the transistors.

 

[mike49504]

Q131 connects to it. (C3198) between legs 2 and 3 i get 2.5 ohms in the board.

 

[Perry Babin]

Remove it and reinstall the 1266. Does the amp power up?

 

[mike49504]

I replaced Q130,131,132 cause they were reading bad . Put the 1266 back in for a min and amp still does the same thing it wont power up

 

[Perry Babin]

You should have replaced the first one you found defective then removed the others one at a time to try to determine which channel or transistor was causing the problem.

 

[mike49504]

If i pull Q31 out amp will power up and idle perfect.

 

[Perry Babin]

131?

There is one transistor from each channel (connected to an emitter resistor). Those two drive Q131. Reinstall Q131 and remove the other two, one at a time to see which one causes the amp to shut down.

 

[mike49504]

If i pull Q230 amp poiwers up I think Q230 controls the left channel.

 

[Perry Babin]

Do both channels produce clean audio?

If so, does Q230 connect to any of the emitter resistors?

 

[mike49504]

Both channels produce clean audio . Yes Q230 connects to the emitter resistors.

 

[Perry Babin]

Did you previously replace this transistor? If not, check it and replace it if necessary.

Are there any bad solder joints on the emitter resistor it's connected to?

Is the emitter resistor out of tolerance?

There are two connections to the emitter resistor. One terminal of the transistor will connect directly to the emitter resistor. The other connection will likely be through a resistor (but could also be directly connected).