blew 3 amps. same issue. help please

[tenaciousNoob 0]

 So I inherited this situation but I'm too deep now to give up.  From what I understand, there was one `1200 watt audio pipe hooked up in dudes car. He blew that one. Then he put 2 more in and blew both of them immediately I believe. Seems like a short somewhere in his vehicle to me but I'm no expert. So I went through and tested all the transistors and found multiple output mosfetts to be blown on all 3 amps. I pieced enough "good" irf640 mosfetts together to hopefully make a working unit but I have a short someoene because It bounces bavck from protesct to power.  Can anyone help me with this?I have more hours in troubleshooting these things than I care to admit.

 

THank you very much

 

[Jay-C76 333]

First: Welcome to SSA thanks for joining and we as a community hope we can help!

Check voltage at amp (before stereo is on & when playing music), wire size of power & grounds (undersized or multiple splices of junk wire), look for any through metal or edge of metal rubbing that could cause shorts in wire runs, check that the subs are not wired in such a way that there is too low of an ohm load for the amp specifications, check each sub for any blown coils by doing a resistance test ( if dual voice coil check each set of teminals on sub), and most commonly if all of the above are okay the gain is set way too high and causing signal clipping. Remember the gain or sensitivity dial on an am is never to be used as a volume knob. It is there to match the sensitivity of the output voltage coming from the head unit or source. 

Basic install skills are what I would trace first, then settings of equipment would be the end phase of problem solving. In my experience one of the most common causes of equipment failure with a d.i.y. install that's not a wiring issue would be the lack of understanding what a gain or sensitivity knob actually is for.

 

Edited March 3, 2018 by Jay-C76

[altoncustomtech 773]

Verify the sub wiring as well and make sure he doesn’t have it wired to .25 ohms or something like that. 

[tenaciousNoob 0]

Thanks for the replies. I took off all the transistors on all the amps and tested them all. in input fets and diodes tested ok., more than half the output irf640s were blown. So, I pieced 8 working ones together and put them on one amp. It goes to protect mode then shuts off. Also, I have it powered by an xbox 360 power supply pushing a bose accoustamass home theater sub just to test.  Should I try buying new fets and see what happens. Thinking about making an osiloscope to test it properly. Any suggestions?I've at this for way too long. Thanks.

[altoncustomtech 773]

Ooooo, got the full picture now. 

You’re definitely going to need to test it further. Chances are those output fets took something with them when they lit off. An oscilloscope would help, knowing what voltages and signals you should see at specific locations would be much more helpful. Unfortunately without a troubleshooting spec or at least design specs that information is probably not available. Without knowing what it should have and where it’s going to be really hard to troubleshoot much further. Perhaps borrowing a working one to compare it to would help but I doubt you have one available. 

Good luck, I know how it feels to put time and/or money into something and not get successful results. 

[tenaciousNoob 0]

I emailed the company to see if I can get a voltage schematic. We'll see how their customer service is. I wonder if I could even send one in and have them tell me whats wrong with it if I can't figure it out

[altoncustomtech 773]

1 hour ago, tenaciousNoob said:

I emailed the company to see if I can get a voltage schematic. We'll see how their customer service is. I wonder if I could even send one in and have them tell me whats wrong with it if I can't figure it out

The second point is very likely, the first will surprise me.  Of course it all depends on the company but there’s plenty of them who probably don’t even have that information because they don’t actually repair anything in house. Others that do want people to send in the defective equipment to their authorized service center. By keeping that information private they can afford to maintain the service center. Either way it sure doesn’t hurt to ask, and if they do have the information available and they’re willing to share it you’ll definitely be in business and finishing the repair will be highly likely. 

[Tirefryr 1,742]

The first problem is your power supply.  It's only 12A at 12.2VDC according to MS specs.  Even low volume testing will undoubtedly induce and under voltage and/or under current situation which would almost certainly shut the amp down or throw it into protect mode.   Hook it up to a car battery and see what happens.