CROSSFIRE VR705D

[bdgf2004]

Pin 1: 12.72
Pin 2: 0.039
Pin 3: 2.56
Pin 4: 0.809
Pin 5: 0.007
Pin 6: -11.28
Pin 7: 0.019
Pin 8: 3.704
Pin 9: -0.855
Pin 10: -1.072
Pin 11: 3.415
Pin 12: 0.019
Pin 13: 3.705
Pin 14: 3.707

 

[Perry Babin]

Are there any components missing from the amp at this time?

 

[bdgf2004]

Thats with everything in place

 

[Perry Babin]

Is there significant DC on the center legs (or tabs) of the output transistors?

 

[bdgf2004]

0.9v

 

[Perry Babin]

With the voltages you posted for the B52 IC, I'd expect to see rail voltage on the drains of the FETs. Is the amp producing both positive and negative rail voltage (check on the source legs of the output FETs)?

 

[bdgf2004]

i have + & - rail voltage on all the outputs source and 0.75v on the drain.

 

[Perry Babin]

Can you post a photo that clearly shows the labels for the driver board (the ones silkscreened onto the main board)?

 

[bdgf2004]

pic

 

[Perry Babin]

Do you have a square wave on the 'in' pin of the driver board?

What is the DC voltage on that pin?

 

[bdgf2004]

I don't see a square wave on the "in" pin.
The DC voltage is at 3.313v.

 

[Perry Babin]

There should be 12v Zener diodes on the driver board (likely silver/gray). Do you read 12v across each of them?

 

[bdgf2004]

i found 3 grey zeners but i only have 12v on 2 of them.

 

[Perry Babin]

Do the two connected to the red resistors have 12v on them?

 

[bdgf2004]

1-yes 1-no

 

[Perry Babin]

Check the one that doesn't have 12v across it. Is it leaking or shorted?

 

[bdgf2004]

the diode appears to be okay

 

[Perry Babin]

Is the resistor feeding the diode open?

 

[bdgf2004]

both of the red resistors read 3300 ohms. but near the one with no voltage there are two surface mount components missing. one is D38 and the other is R71. i would have mentioned this before but it is not uncommon for me to see a circuit board with empty spaces.

 

[Perry Babin]

For the Zener that had no voltage across it, follow the circuit back from that diode (the end that doesn't connect to the red resistor) to the board's connector. What's the marking on the main board for that pin of the connector?