Amp troubleshooting help

[Name'sDEEZ]

A friend of mine brought me multiple amps with the same stories that he bought them and when he installed them that they just went dead. (Fuses, smoke etc.) I know that hes not telling me everything. On one amp i connected correctly but as soon as i connected the power on battery i got the whiff of burning smell. So i disconnected. On second try it poped fuses as soon as i put music. Everything was on low settings on amp and head unit when i connected it.

Second amp i going to test he says that it powers on but no power to speakers. So before i even plug it in what else can i check?

Ive already opened and inpected them i believe him when he said brand new. So what am i missing?

Oh and when he handed them to me the gains were almost maxed if that helps.

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[Deiimos]

When powering on an unknown amp, use a current limiter. A quick method is to hook it up with a 10 amp fuse in line (for smaller amps), real tiny amps maybe a 5 or 7 amp fuse, bigger amps 15 amp fuse. This way if something is wrong you don’t get extremely fried parts, just a blown fuse. Can also power an amp up through an old automotive light bulb which will limit how much current goes into an amp, I forget the model bulb, but use to use a taillight bulb that only allowed about 2 amps to pass. It is typically enough to let an amp idle for basic testing, and if there is a fault with the amp the lightbulb simply glows full brightness.

Anyway, the amp that let out smoke sounds like dead power supply MOSFETs and associated parts, possibly bad output transistors as well.

If you have a digital multi-meter, you can take the cover off and check the MOSFETs for shorts before you even apply power. Or simply install a low value fuse before powering on the next one. You didn’t mention the amp model, so all I can say is start with perhaps a 10 amp fuse in line, if it doesn’t blow that then continue your testing for output as normal, leave the 10 amp in until your ready to test for high output. If it does blow the 10 amp while its charging its rail capacitors, you could possible try a 15 amp, some amps pull a lot of current at startup.

If these are some insane 5 - 10KW amps then this might not be applicable.

 

[Name'sDEEZ]

When powering on an unknown amp, use a current limiter. A quick method is to hook it up with a 10 amp fuse in line (for smaller amps), real tiny amps maybe a 5 or 7 amp fuse, bigger amps 15 amp fuse. This way if something is wrong you don’t get extremely fried parts, just a blown fuse. Can also power an amp up through an old automotive light bulb which will limit how much current goes into an amp, I forget the model bulb, but use to use a taillight bulb that only allowed about 2 amps to pass. It is typically enough to let an amp idle for basic testing, and if there is a fault with the amp the lightbulb simply glows full brightness.

Anyway, the amp that let out smoke sounds like dead power supply MOSFETs and associated parts, possibly bad output transistors as well.

If you have a digital multi-meter, you can take the cover off and check the MOSFETs for shorts before you even apply power. Or simply install a low value fuse before powering on the next one. You didn’t mention the amp model, so all I can say is start with perhaps a 10 amp fuse in line, if it doesn’t blow that then continue your testing for output as normal, leave the 10 amp in until your ready to test for high output. If it does blow the 10 amp while its charging its rail capacitors, you could possible try a 15 amp, some amps pull a lot of current at startup.

If these are some insane 5 - 10KW amps then this might not be applicable.

Thank you for the reply.

The one that let smoke out was a scosche hd2250 that i think he overload it and i got to see the smoke.

The other amp ive yet to test is a hifonics zeus zrx2416.1d i was waiting for fuses but you clearly answered a big questioned i had about powering amps with lower rated fuses so big thanks.

When checking mosfets for shorts what should i be looking for in the multimeter?

 

[Deiimos]

An amp like the Schoche would start with maybe a 7 amp fuse for initial testing, no higher than a 10 amp. It’s obviously blown, so I wouldn’t worry about that now though.

The Hifonics would probably need a 15 amp fuse, could try a 10 obviously first. If both of those sizes blow, then highest to try would be 20 amp, but I wouldn’t go higher than that and would start with the lower fuses first. If it just blows the fuses, it likely has some bad transistors.

Zero ohms from drain to source, or near zero ohms = bad MOSFETs, often all three terminals end up shorted so is quick to tell if they are bad. The Schoche amp probably uses bipolar output transistors (I'm not sure though). If you need detailed help troubleshooting the amps, I'd highly suggest signing up at https://www.diyaudio.com/community/forums/car-audio.38/ and posting each amp in a separate thread in the car audio section (so just one amp at a time in its own thread to minimize confusion). A couple guys there that are very knowledgeable and may help try to walk you through testing / repair if you can follow the instructions carefully. It's the best site if you want real help with car amplifier repair though. It isn't a typical car audio forum, that section is mainly just repair help.

And no problem, hopefully you get the amps figured out. Amp repair can be fun, or a nightmare depending.

 

[Name'sDEEZ]

An amp like the Schoche would start with maybe a 7 amp fuse for initial testing, no higher than a 10 amp. It’s obviously blown, so I wouldn’t worry about that now though.

The Hifonics would probably need a 15 amp fuse, could try a 10 obviously first. If both of those sizes blow, then highest to try would be 20 amp, but I wouldn’t go higher than that and would start with the lower fuses first. If it just blows the fuses, it likely has some bad transistors.

Zero ohms from drain to source, or near zero ohms = bad MOSFETs, often all three terminals end up shorted so is quick to tell if they are bad. The Schoche amp probably uses bipolar output transistors (I'm not sure though). If you need detailed help troubleshooting the amps, I'd highly suggest signing up at https://www.diyaudio.com/community/forums/car-audio.38/ and posting each amp in a separate thread in the car audio section (so just one amp at a time in its own thread to minimize confusion). A couple guys there that are very knowledgeable and may help try to walk you through testing / repair if you can follow the instructions carefully. It's the best site if you want real help with car amplifier repair though. It isn't a typical car audio forum, that section is mainly just repair help.

And no problem, hopefully you get the amps figured out. Amp repair can be fun, or a nightmare depending.

Big thanks for the tips and link i will test the hifonics how you said. Its a good thing i didnt go at it with the higher amp fuses now. Yea right now its a nightmare idk how this guy does it to blow things out. He brought me this sundown 3000 amp with half the mosfets blown along with 2 caps and then these 3 amps. The one i didnt mention was a RF punch with a ground terminal missing. Lol

But when looking at mosfets do i just replace with an equal rated one right?

 

[Deiimos]

Out of curiosity, which model Rockford is it?

Yes you replace with the same exact part, and all in the same parallel group. If the parts are obsolete / no longer manufactured, you can run into problems substituting and this is where you need an oscilloscope to help make sure whatever you sub in, is going to work okay and not run hot, etc., sometimes it takes a bit of testing, sometimes you may not find a good replacement. Some amps are very picky with what MOSFET's you install, others you might need to change a resistor value to make them work properly.

Like I said, that forum is the best you will find for someone willing to actually walk you through a repair, if you can follow instructions well.

If you are more serious about car amplifier repair, the BCAE1 car amplifier repair tutorial, is very in-depth (created by Perry Babin who helps people repair amps at that diyaudio forum, extremely knowledgeable guy, if he can't walk you through a repair, nobody can).

 

[Name'sDEEZ]

Out of curiosity, which model Rockford is it?

Yes you replace with the same exact part, and all in the same parallel group. If the parts are obsolete / no longer manufactured, you can run into problems substituting and this is where you need an oscilloscope to help make sure whatever you sub in, is going to work okay and not run hot, etc., sometimes it takes a bit of testing, sometimes you may not find a good replacement. Some amps are very picky with what MOSFET's you install, others you might need to change a resistor value to make them work properly.

Like I said, that forum is the best you will find for someone willing to actually walk you through a repair, if you can follow instructions well.

If you are more serious about car amplifier repair, the BCAE1 car amplifier repair tutorial, is very in-depth (created by Perry Babin who helps people repair amps at that diyaudio forum, extremely knowledgeable guy, if he can't walk you through a repair, nobody can).

I joined the forum right after you mentioned it and yea theyre serious about the repairing and such lol i got a glimpse. But yea when the problem is deeper then what i understand i just leave it alone. So i will be testing the hifonics tonight the way you suggested and from there ill see whats going on atleast.

The rockford is a punch 700 i belive ill give a better answer once im home

 

[Name'sDEEZ]

Out of curiosity, which model Rockford is it?

Yes you replace with the same exact part, and all in the same parallel group. If the parts are obsolete / no longer manufactured, you can run into problems substituting and this is where you need an oscilloscope to help make sure whatever you sub in, is going to work okay and not run hot, etc., sometimes it takes a bit of testing, sometimes you may not find a good replacement. Some amps are very picky with what MOSFET's you install, others you might need to change a resistor value to make them work properly.

Like I said, that forum is the best you will find for someone willing to actually walk you through a repair, if you can follow instructions well.

If you are more serious about car amplifier repair, the BCAE1 car amplifier repair tutorial, is very in-depth (created by Perry Babin who helps people repair amps at that diyaudio forum, extremely knowledgeable guy, if he can't walk you through a repair, nobody can).

Rockford fosgate punch 7001s

 

[Deiimos]

Can't say I remember seeing that specific model. Do you know if that is a newer or older amp? I remember the 20 year old 700S and the various similar models.

 

[Name'sDEEZ]

Can't say I remember seeing that specific model. Do you know if that is a newer or older amp? I remember the 20 year old 700S and the various similar models.

From what a reviewer named juggalo john said in 2014 this might of been the 20 yr old model. This is the biggest option in the line up the one without a fuse. You could be right.

 

[Name'sDEEZ]

Can't say I remember seeing that specific model. Do you know if that is a newer or older amp? I remember the 20 year old 700S and the various similar models.

Off topic from the started question but sticking to rockford fosgate. I have RCA cables from rockford that have the 2 rca plugs but a 3 little wire in between them. Do you know the purpose of the 3rd wire?

 

[Deiimos]

Off topic from the started question but sticking to rockford fosgate. I have RCA cables from rockford that have the 2 rca plugs but a 3 little wire in between them. Do you know the purpose of the 3rd wire?

I used it as a remote turn on wire and I would guess most others did too. I've had a few different sets of RCA's like that, even some Rockfords 20 years ago if I recall.

 

[Deiimos]

From what a reviewer named juggalo john said in 2014 this might of been the 20 yr old model. This is the biggest option in the line up the one without a fuse. You could be right.

Yeah if it looks like that amp I remember those style well. Same board as the old 800a2, 800.2, 801S etc, from the early 2000's. Solid amp and worth repairing, though you have to know what you're doing with the MESHA strips the MOSFETs are soldered to, very different than most other amps and easily destroyed if not careful.

 

[Name'sDEEZ]

Yeah if it looks like that amp I remember those style well. Same board as the old 800a2, 800.2, 801S etc. Solid amp and worth repairing, though you have to know what you're doing with the MESHA strips the MOSFETs are soldered to, very different than most other amps and easily destroyed if not careful.

Yea what i did was just soldered on a 4ga wire with a terminal so i can bolt on my power supply. And voila amp turned on.

 

[Name'sDEEZ]

I used it as a remote turn on wire and I would guess most others did too. I've had a few different sets of RCA's like that, even some Rockfords 20 years ago if I recall.

Yea sounds like they are. I found em in storage boxes that my pops wanted to get rid off