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Old 23rd January 2011, 05:23 PM   #1
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Default CROSSFIRE VR705D

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.
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Old 23rd January 2011, 06:23 PM   #2
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Please post a photo of the driver board and the class D section of the amp.
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Old 23rd January 2011, 06:45 PM   #3
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the pics
Attached Images
File Type: jpg crossfire class d section.jpg (159.3 KB, 73 views)
File Type: jpg crossfire driver board .jpg (146.6 KB, 70 views)
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Old 23rd January 2011, 06:49 PM   #4
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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?
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Old 23rd January 2011, 07:09 PM   #5
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center leg has 0v on all outputs. the 640's both have -47v and the 9640's all three have 47v
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Old 23rd January 2011, 07:21 PM   #6
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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).
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Old 23rd January 2011, 07:48 PM   #7
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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?
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Old 23rd January 2011, 07:50 PM   #8
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I think those should be a good sub but I'm not 100% sure.
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Old 23rd January 2011, 08:13 PM   #9
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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?
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Old 23rd January 2011, 08:37 PM   #10
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The dimple is a dashed line which indicates that it's not visible and is on the other side of the object.
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