Reverse polarity on Power inputs

spooney · 18th December 2007, 10:05 PM

How much damage is typical of a small to medium sized amp that has had the polarity reversed on the power inputs?Only reason I ask is because i've seen one for sale and I was considering buying it to try to repair.

Perry Babin · 18th December 2007, 10:13 PM

If it was properly fused, there may be no damage.

If it was not properly fused, it may have blown the reverse protection diode (if it had one), the PS FETs and the power supply driver IC. If there were op-amps on the primary side (used in the protection circuits), they may have failed also. It could also have open traces.

Generally, if this happens, the damage isn't expensive to repair unless it's a large amp.

xtaltech · 18th December 2007, 11:24 PM

The consequences can be medium to big.

If the equipment was protected by a fuse the damage area might be limited to the output hybrid module. Without a fuse, the equipment would smoke or even catch fire.

Good luck!

jol50 · 20th December 2007, 01:17 AM

I have an amp right here that had a smoked ground to the case, then I see the ground is blown near the power terminal also thus killing the amp. Do not see any shorts on the outer case but they could have hooked it up wrong. Have not fixed yet so don't know if it did other damage, but most things test good in there; diodes/PS/outputs. It burned the solder right off two jumpers to the case ground screw. Its about 1000w. Only so many reasons it would do that. However the bottom cover is worn in a spot where it rubbed on metal possibly. I still go old school and never mount amps on metal.

I've seen a bunch of amps that did not work, they were cheap and had a burn spot on the case....blew the ground trace every time in that amp. Or they put the 12v on the ground terminal with it touching metal. A few had other issues. They came with boxes I was buying but I did end up fixing most of them and selling them for $20 each....for fun I guess.

Perry Babin · 20th December 2007, 04:24 AM

There's no reason that you can't mount an amplifier to the chassis of the vehicle.

There's no designer/engineer that would design an amp for an automobile that would have problems if the casing made contact with the vehicle chassis.

jol50 · 20th December 2007, 04:38 AM

It has been a long time, but back when I installed we were not even allowed to mount an amp touching metal. Maybe it was noise issue or some strange amp they sold there I can't remember now (mostly LP, pioneer, kenwood...maybe for GM120s). There is rarely a good place to mount an amp on metal in a car anyway....but yes the ones I have looked at the case is grounded.

That amp worked BTW, it was just a blown ground. The PS had power but the driver did not.

18th December 2007, 10:05 PM	#1
spooney diyAudio Member Join Date: Dec 2006	Reverse polarity on Power inputs How much damage is typical of a small to medium sized amp that has had the polarity reversed on the power inputs?Only reason I ask is because i've seen one for sale and I was considering buying it to try to repair.

18th December 2007, 10:13 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If it was properly fused, there may be no damage. If it was not properly fused, it may have blown the reverse protection diode (if it had one), the PS FETs and the power supply driver IC. If there were op-amps on the primary side (used in the protection circuits), they may have failed also. It could also have open traces. Generally, if this happens, the damage isn't expensive to repair unless it's a large amp. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

20th December 2007, 04:24 AM	#5
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	There's no reason that you can't mount an amplifier to the chassis of the vehicle. There's no designer/engineer that would design an amp for an automobile that would have problems if the casing made contact with the vehicle chassis. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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18th December 2007, 11:24 PM	#3
xtaltech diyAudio Member Join Date: May 2004 Location: the Constitution State	The consequences can be medium to big. If the equipment was protected by a fuse the damage area might be limited to the output hybrid module. Without a fuse, the equipment would smoke or even catch fire. Good luck!

20th December 2007, 01:17 AM	#4
jol50 diyAudio Member Join Date: Nov 2007	I have an amp right here that had a smoked ground to the case, then I see the ground is blown near the power terminal also thus killing the amp. Do not see any shorts on the outer case but they could have hooked it up wrong. Have not fixed yet so don't know if it did other damage, but most things test good in there; diodes/PS/outputs. It burned the solder right off two jumpers to the case ground screw. Its about 1000w. Only so many reasons it would do that. However the bottom cover is worn in a spot where it rubbed on metal possibly. I still go old school and never mount amps on metal. I've seen a bunch of amps that did not work, they were cheap and had a burn spot on the case....blew the ground trace every time in that amp. Or they put the 12v on the ground terminal with it touching metal. A few had other issues. They came with boxes I was buying but I did end up fixing most of them and selling them for $20 each....for fun I guess.

20th December 2007, 04:38 AM	#6
jol50 diyAudio Member Join Date: Nov 2007	It has been a long time, but back when I installed we were not even allowed to mount an amp touching metal. Maybe it was noise issue or some strange amp they sold there I can't remember now (mostly LP, pioneer, kenwood...maybe for GM120s). There is rarely a good place to mount an amp on metal in a car anyway....but yes the ones I have looked at the case is grounded. That amp worked BTW, it was just a blown ground. The PS had power but the driver did not.

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