MTX Black Gold BGA2125 Amp in protect mode

[JBigDog]

Hello, i got this amp cheap because the FETs were blown. It turns out this Amp is pretty rare and is supposed to be a beast. I replaced the FETs and still had a high current problem which turned out to be a shorted capacitor, one of the little green rectangle ones which is the first shorted cap i have ever seen in my 30 years of playing with electronics which wasnt an electrolitic cap. Anyways, now amp shows about 1amp current draw and 2amps with speakers attached but all i can get it to do it come up with a LED labeled "FLRC" light up which i cant figure out what that even stand for. Im assuming its protection mode of some sort.? Since this amp is rare, i cant find any info on it. I am stuck as to where to go from here. What the h3ll does FLRC stand for and where should i start in order to fix the issue?

Any help would be much appreciated.!

 

[Perry Babin]

Floating RCA shield ground? If so, the fix is to use a signal source that's grounded to the same power supply that you're using to power the amp.

Before you try the other signal source, disconnect the RCAs and measure the resistance from the B+ terminal to the non-bridging speaker terminals. It should not be anywhere near 0 ohms.

 

[JBigDog]

From the 12v terminal to the non-bridged (i think i got the right ones, it goes neg-pos neg-pos so I'm assuming the outside terminals are the bridging ones) terminals, it goes 1.2M ohms positive term and 4k to the neg terminal.

 

[JBigDog]

I don't know how close the rail voltages are supposed to match but i got - 36.2 and 39.1. I could see some kind of protection of those 2 voltages were too far off equal distances from common ground. Just throwing stuff out there that might be of interest to those with more knowledge on these things. .

 

[Perry Babin]

Place the black probe on the non-bridging speaker terminal and re-check the rail voltage.

If you read something in the mega-ohm range from B+ to the N-B speaker terminals, you can ground the RCA shields to see if the FLRC LED goes out.

 

[JBigDog]

With the black probe on the n-b terminal, i got - 36.8 and 39.2 for rail voltages.

I grounded the rca shields and flrc light is still lit. . Power LED does nothing as that's the way it has always been. .

 

[JBigDog]

There are 3 daughter cards in this thing, 2 of them are identical, the 3rd looks like it feeds the FLRC light so in taking a better look at it, 2 resistors have been heated a little too much, R19 and R13. . The discoloration makes it impossible to read the color bands in order to replace them. Also R22 is missing. Don't know if that's on purpose or not. Looks like a mod was done presumably by MTX as Q3 has a leg cut off and a wire ran from it to R21 for an engineering change after the boards were produced. Wish i knew someone with one of these to verify resistors and missing part. .

 

[Perry Babin]

Can you see anything useful on the following site:
MTX Black Gold BGA 2125

 

[JBigDog]

Ya actually that did. I can see that the mods to the daughter board was not done and the resistor missing on mine is there. . I'm attaching the pic blown up and the part in question circled. Anyone want to take a guess at what the resistor in question is? Want to see if your guess matches mine.

Thanks!

 

[Perry Babin]

Red, violet, red, gold would be my guess. It looks like the second band could be black but a 2.0k isn't nearly as common as a 2.7k.

 

[exetron]

Internal amp pictures

MTX Black Gold BGA 2125
has details about this amp
check out the circuit that connects to the FLRC led

check out the TL 494 amp chip


MTX Audio Headquarters
4545 E. Baseline Road
Phoenix, AZ 85042
602-438-4545

MTX Amp Service Center
800 225-5689
Maybe you can get some answers from them