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Old 19th January 2014, 02:50 AM   #1
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Default Repairing Orion 2500D - Need help

Ok, so I am fairly new to repairing amplifiers, but this is not my first one. I have dabbled in it for years, fixing 1 or 2 here and there over the years,a few months ago I started doing it more as a real hobby and to make a bit of extra money. Ive repaired quite a few over the last few months, but I am no expert and this one has me stumped.

When I received the amplifier. The power supply section was fine, but the output section was toasted. The amp would actually power up and play, but had an extremely distorted output. Many of the outputs were clearly shot on both sides of the amp, as well as the gate resistors. I replaced the outputs on both sides of the amplifier. IRF9640 (x20) and IRFB31N20D (x12). I also replaced all of the gate resistors on both sides as well (10R0).

There are two driver boards on this amplifier. One handles the FETs on one side of the amp, and the other handles the opposite side. The driver board that handles the left side (when looking at the amp from the signal input section side), had a few of the P-channel FET drivers blown. I replaced the driver's accross the entire board for both P and N channel FETs. (C1027, A1023) I also replaced all of the 1R0 resistors in between the drivers (Emitter follower configuration). I replaced these for every set of drivers, even if they tested good. The Zener diode on the P-channel side was blown as well so i changed them on both sides. Everything else I tested on the boards tested good.

When I would power up the amp the power light would just flash on and off quickly. (protect)

So I decided to cut the trace from the PWM board to each driver board. When I would connect only the trace to the driver board for the right side FET's, the amp would power up with no protection, no excessive current draw, and no DC Offset. When I would connect only the trace for the driver board that handles the left side FETs, the amp would again flash the power light.

So I then disconnected the traces from the left side driver board, to each of the gates of the left side FETs. When I would reconnect the traces to the P-channel FETs, I could get the amplifier to power up with no protect. But when I would try to power up EITHER bank of N-channel FETs, the amp would go back to its protect state.

So basically I can have everything on the amp connected and powered up on both sides EXCEPT the N-Channel FETs on the left side without going into protect mode.

Where should I look??? Anybody have any tips where I should look?? What should I test for?

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Old 19th January 2014, 04:48 AM   #2
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If I need to post more info, or test anything just LMK. I will provide anything I can to help figure this out.

Also, when I said there was no DC offset when it does not go into protect (With the Left side N-channel FETs disconnected), I get 35mv across the +/- terminals. Is that an acceptable level? I was under the impression <1V was reasonable.
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Old 20th January 2014, 04:27 AM   #3
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So I was mistaken. I can power up either the N-channel FETs OR the P-channel FETs on the left side with no problem. But I cannot power up both at the same time.

What the heck could cause this? I rebuilt the driver board for a second time, just in case. Still the same issue. If I cut the PWM trace to the board everything is ok, but as soon as I re-connect it, it goes into protection if both N and P channel gates are connected. Could it be the "A393F" IC on the driver board, possibly trying to power both sets of FETs at the same time? Or maybe the PWM?
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