Mach 460 rear amps Fix (Also new cobra owner!)

[286rocks]

Hi all, I just picked up a new to me 01 cobra last weekend, so far the car is a blast and I love it! However when I bought it the 2 rear amps were not working... like so many other stang owners from what I have been reading. :nonono: After doing all the normal checks, speaker impedance, 12v, turn on, etc. I decided to pop the amps open and take a look at the PCB. What I found is that resistor #808 was burnt in both amps.

Here is where the resistor is...sorry for the bad pictures, I didn't have a lot of light to work with.

Because I am so damn cheap and would like to keep the car as stock as possible I decided to try and fix them myself. The resistor is a 1/4 watt, 91 Ohm piece (color code: White, Brown, Black) and from what I could tell it had a 10% tolerance. The resistor was really burnt so I could barely make it out.

To fix it I took a trip down the the local Rat Shack and picked up a pack of 91 Ohm resistors, I decided to step up to some 1/2 watt pieces to keep them from just burning up again. These were a bit bigger and required some filing on the leads in order to get them through the PCB but they fit well. I also made sure that they had a 5% tolerance, instead of the 10% that the removed ones had. (You can tell the tolerance by the color of the forth band, Gold=5%, Silver=10%)

The soldering isn't too hard if you've had any time behind an iron, some good copper solder wick, and a solder sucker do make the job easier.

After I wrapped everything up and put the amps back together, I plugged them right in and BAM! I again had mids and lows! They've been working for a few days now with no signs of failure, but I'm keeping the rear seats down and keeping an open nose for burning smells just in case. lol. I know most people just rip the stocks amps out and replace them when they fail, but hopefully someone out there can make use of this.

 

[IUP99snake]

That's an AWESOME fix. It's really rewarding to be able to fix little things like that on your own using parts that you found yourself instead of having to replace the entire thing and spend a lot of money.

Glad to hear that it worked out well for you. I'll keep this in mind if my amps ever quit working.

I just did a neat electrical project on my motorcycle that was just as rewarding. I have a Triumph Daytona 675 with a bad voltage regulator. It's almost like the factory voltage regulators are designed to fail like clockwork. (This was my second one) And they are expensive. Rather than buying a new one for $150, I went on eBay and bought a voltage regulator from a Honda CBR600. It has newer MOSFET circuitry rather than the "Shunt" type regulator than the triumph came from. Best of all, it was less than $40. All I had to do was cut off the pigtails from the triumph regulator and solder them on to the Honda regulator so it would plug in using the factory wiring. Worked like a charm!

Nice work!

Homer

 

[99Venom]

Very nice work! Good job of investigating it yourself and fixing it the right way.

I had the same problem a while back but I found a cheap replacement for the whole rear deck so it worked out that time, but if it ever fails again I know where to start looking.

 

[Wynn]

You seem to know your stuff. My amps are acting up too. They sound fine, but they drain the battery when the car is shut off. I have to pull the Audio fuse to keep the battery from dying. Any idea what to look for? I actually have the amps in my room right now and was going to just buy new ones, but maybe I can fix it myself.

 

[greenscobie86]

SORRY TO BRING THIS BACK FROM THE DEAD! [/yelling]

I wanted to give kudos to the OP as I just did something similar on my 1998 Ford Expedition with Mach Sound.

The subwoofer amp is exactly the same as the one's in the mustangs with the exception of 2 more wires which needed re-soldering(PCL1 RED and PCL2 yellow) at the bottom right of the main connector on the amp. The Expedition has these for whichever reason.

My original amp has a burnt R807 resistor so thanks to this thread I'll be able to go and spend a few bucks to fix the amp.

Cheers!

 

[286rocks]

Wow, I forgot all about this thread! Glad someone got use from it though.

Wrynn:

The first thing I would check is to see if the amps are getting a turn on signal while the car is off with the ignition off. Check the plugs going into each of the 3 amps and look for a pin that has +5VDC. If you find one this is what is causing your battery drain.

If you're still having the issue and you do indeed find 5 volts on the turn on wire; let me know and I can step you through jumping it to a new 12v key on source. After than I can take you through diode isolating and stepping down the voltage to work with the Mach amps.

 

[Doch01]

Nice job

 

[52merc]

Thanls for the post

I have had my '01 Cobra since new and had no problems with battery drain for many years. Just last year I had to get a battery tender for the winter storage period or the battery would die (used to last all winter and fire right up in the spring). Starting about 2 months ago, if I let the car sit for more than a week....dead battery.

After an exhaustive but systematic check of the electrical system I found the culprit to be the passenger side Mach 460 amp. Removed it from the car and opened it up. Sure enough, resistor R808 was badly burnt and R807 was slightly burnt. I was figuring I'd have to take the other amp apart to find out what resistance it was so I could replace it. Then I found this post using a Google search. Great info and I want to thank you. I'm going to see if I can replace the resistors and get it to stop "leaking" current. The amp was still functioning when I had this problem.

What I really want to know is if the change to the larger wattage solved the problem and is your amp still working? Should I consider making the same change to the other amp as a preventative measure?