I have this huge, brand new, American Bass VFL 500.1 amplifier in for repair and there is no reverse polarity protection built into the circuit or fuses for that matter.
I think this amplifier was connected backwards to the B+ and ground. Every single mosfet in the power supply was shorted gate to drain and most were shorted gate to source. There are 24 mosfets in the power supply and 4 transformers.
Three of the output mosfets were shorted as well. So I’ll be replacing 8 of the output mosfets. Probably will have to do some work on the output driver card as well. But I haven’t gotten that far with it.
My question is, would you try to add some reverse protection diodes to prevent this from happening again. I don’t want this amp to boomerang on me due to some else’s mistake.
I’m not sure what diode to use or how many to use as a reverse protection. I was thinking of scabbing some on the bottom of the board.
Does anyone have any other thoughts on this idea? Good or bad.
David
I think this amplifier was connected backwards to the B+ and ground. Every single mosfet in the power supply was shorted gate to drain and most were shorted gate to source. There are 24 mosfets in the power supply and 4 transformers.
Three of the output mosfets were shorted as well. So I’ll be replacing 8 of the output mosfets. Probably will have to do some work on the output driver card as well. But I haven’t gotten that far with it.
My question is, would you try to add some reverse protection diodes to prevent this from happening again. I don’t want this amp to boomerang on me due to some else’s mistake.
I’m not sure what diode to use or how many to use as a reverse protection. I was thinking of scabbing some on the bottom of the board.
Does anyone have any other thoughts on this idea? Good or bad.
David
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They don't do much in amps because the intrinsic diode in the FETs will conduct when there is reverse voltage. Also, to have a protection in the form of a diode that can survive the fuse that large amps require is significant.
That said...
Even a small RP diode can be useful in that, if it's blown, it gives you proof that the amp was connected with reverse polarity.
If you want something that might survive, multiple MUR820 type rectifiers might work. You can solder the tab to the positive pour/trace. The leg for the other side of the internal diode can be soldered directly to the ground if you find a convenient place to catch both B+ and ground.
That said...
Even a small RP diode can be useful in that, if it's blown, it gives you proof that the amp was connected with reverse polarity.
If you want something that might survive, multiple MUR820 type rectifiers might work. You can solder the tab to the positive pour/trace. The leg for the other side of the internal diode can be soldered directly to the ground if you find a convenient place to catch both B+ and ground.
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