CROSSFIRE VR705D

[bdgf2004]

i picked up this 5-ch amp the other day when i first opened it i found a shorted output in the 4-ch section. all the resistors and drivers checked out ok so i replaced the shorted output (2SD718) and now the 4-ch section works perfectly. so i started testing it out and when i plugged my rca's into the subwoofer section the muting relay started to switch on and off and the protect light will blink. i removed 2 of 5 outputs (IRF9640/640) to get a more accurate reading and they seem ok so i reinstalled them. i currently have the driver board removed, i haven't pulled any of the parts from the driver board yet. i was curious so i powered the amp up with the driver board removed and plugged in the rca's now it will stay on. this is basically 2 amps in 1, it has 2 seperate power supplies and everything. it pulls a little current when powered up but i figured it was probably normal because it's just like powering up 2 amps.

 

[Perry Babin]

Please post a photo of the driver board and the class D section of the amp.

 

[bdgf2004]

the pics

 

[Perry Babin]

With the driver board out of the amp and the outputs in the amp, what's the DC voltage on the center legs of the output transistors?

What is the rail voltage on the source legs of the outputs?

 

[bdgf2004]

center leg has 0v on all outputs. the 640's both have -47v and the 9640's all three have 47v

 

[Perry Babin]

I would suspect the A1023s and the C1027s on the driver board. As well as checking them for shorts/leaking, check them to confirm that both junctions of each transistor are intact (they'll need to be out of the circuit to test them properly).

 

[bdgf2004]

the first one i pulled (a1023) appears to be defective. i haven't checked the rest of them yet but would it be ok to try to use the KSC2690 / KSA1220 in there place?

 

[Perry Babin]

I think those should be a good sub but I'm not 100% sure.

 

[bdgf2004]

why is it that on the datasheet for the KTA1023 it shows the legs as 1=E, 2=C, 3=B from the side of the transistor with the dimple. but when i test them it seems to be just the opposite? what am i missing?

 

[Perry Babin]

The dimple is a dashed line which indicates that it's not visible and is on the other side of the object.

 

[bdgf2004]

OOOOOOOOOOOO! thank you very much, that always confused me but i felt stupid to ask. you have all the answers!!!

 

[bdgf2004]

i am now replacing all 4 of the a1023's/c1027's and then i will reinstall the driver board to see what happens.

 

[bdgf2004]

maybe the amp dosn't like the new parts or i still have another problem. the relay will stay on now but the output signal is bad. this is supposed to be a 60hz sine wave.

 

[Perry Babin]

With no input signal, set your scope to AC coupling, 5v/div and 10uS. Do you see a clean square wave on the gates of all of the output transistors?

 

[bdgf2004]

absolutely no square wave

 

[Perry Babin]

Assuming that you had a straight line centered on the display...

Set the scope to 50v/div. Do you have a square wave on the center legs of the outputs?

 

[bdgf2004]

it looks fuzzy but still no square wave

 

[Perry Babin]

Post a photo of the component side of the other vertical board (near the driver board).

 

[bdgf2004]

the tab of U702 is chipped, it was stuck to the heatsink. should i replace it?

 

[Perry Babin]

The broken tab won't matter if the tab doesn't short to the heatsink.

I'm assuming that all of the circuit boards were in the amp when you were looking for the square wave.

Post the DC voltage on the B52 IC.


Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14: