DB Drive 1200

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I am working on a DB Drive 1200 that the power supply mosfets were bad changed and would power up ( with current limiter ) and would go in to protection . Removed rectifiers and powers on and no high current draw. Put back in the rectifiers and the protection light comes on . Took out the output drive boards still in protection . put back in the drive boards . Bypassed the protection on the 494 , turned on high current draw , but when I remove the outputs everything is ok ? All the output transistor test OK good ? Thank you in advance , Hector .
LOL just saw a youtube video about ChipQuik that stuff works ! Will order next time from digikey , Thanks .

Ok I will check on that , makes sense to . I was thinking that I should just order some news for that reason of not being 100% sure. Yes I tested them with diode mode like your web page says to . I didnt know about how the mosfets set to ohms should read open to all other pins . Will report back later . Thank you.
When using CQ to remove driver boards, use the following procedure:

Using this method, you'd apply flux to all of the solder connections and then apply enough CQ alloy so that ~1/2 of the pins of each 5-6 pin group are bridged. After you've applied the alloy, touch your iron to the tip of each pin and heat it until you can move the pin around in the via. Do this for all pins. This helps to promote the mixing of the alloy and the standard solder through the depth of the via. There should still be sufficient alloy on the pins so that ~1/2 are bridged. Now, run your iron back and forth across the pins (not touching the pads). Stay on each group for 3-4 seconds then move to the next group. Two groups are generally the limit when you only have one iron. Go back and forth between the groups of pins. GENTLY try to move the board. When all of the pins are moving, begin to pull the vertical board away from the main board. When done properly, the vertical board will pull out with absolutely no damage to the vias or pads in the main board.
Have you checked all of the outputs to confirm that none are leaking (electrically)?

Yes (2) 9540 and (2) 640 . Iam so happy now I know how to turn them on and now how to check for leakage . Thank you, Perry .

Does this amp use an LM361 (on the driver board behind the RCA jacks)?

Righ behind the RCAs are NJM2068LD JRC3004G (8) , A3003B 16 pin (1) , TL072 smd 8 pin (1) , and one on each drive board A393F 8 pin .
Ok put in place (2) 9540 and (2) 640 outputs good mosfets , now Iam getting hi pitch sound from the power supply mosfets and the led protection led and the on led light (good led) flashed bright and dimmed out burning the both of them . I removed the power led light and it has ground but the + positive side has 43 plus volts ?? Its connected to one end of a zener diode (good) and then to a resistor (good) and then to a mylar cap 9 (it has the 43plus voltage on both sides) then ends at the 2nd transformer side (postive side) ..??
Here is the side of the output ICs


  • DB 1200 END SHOT.jpg
    DB 1200 END SHOT.jpg
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  • DB1200 BACK SIDE.jpg
    DB1200 BACK SIDE.jpg
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  • DB1200 393 SHOT.jpg
    DB1200 393 SHOT.jpg
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Ive taken everything out output drive boards , the board with the 13600, and the board with the F-16 and the B-52, and they do not stop the hight current draw , but as soon as I remove the outputs 9540s, 640s it idles and the the power led turns on bright no more high current draw. The regulators have correct voltage , but when I install the outputs everthing goes to .330 volts on the output side . I am stuck there ? Any ideas ?
9640 1. 55.0v 2. .000v 3. 55.3v
640 1.-55.1v 2. .000v 3.-55.4v

with output drive boards out ,and outputs in .

I was looking at one of the drive boards. I thought one part was a smd cap, but it was a smd resistor it changed from black green to a light white color . Compared to the other drive board the numbers of the parts are the same. It looked like the resistor unsoldered it self a bit cause it is alil lifted from the board but still in place and soldered, and around it was a resin-ish brown color on that spot on the board ( clean now ). The outputs look good so it is going to be a part on the drive boards ? Probably the board with this damage huh ?
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