Phoenix Gold Phorum

I have owned my mps2500 for 18 years now and had one of the caps replaced around 12 years ago( I know should have done them all). I finally have a vehicle that my sub box will fit again so decided to try it out.
It works but only seems to put out around 40% power. Green light stays solid on and clip lights only flash when the gain is set around 80% and the receiver volume is cranked. If I never used this amp before I would think it's running perfect but I know my two 600W rms 15 inch subs should have at least twice as much bass running at 1 ohm.

Opened up the amp and took a better look and noticed a resistor(R331) under one of the red coils is burnt. I'm pretty sure I can replace the capacitors myself but I'm not sure I'll be able to change that resistor because of that red coil(transformer?) on top. Even if I can change it I need to know why it burnt. Is it possible a leaking cap could have caused it? The bass dial is also acting weird. Kinda hard to explain but after the car sits overnight, the subs seem to only get around 10% power until I wiggle the dial and then it goes back to my estimated 40% output and makes a static distortion thru the subs when it's wiggled. I'm thinking it's not related to the resistor but figured I should mention it.

Sorry for the long post. Do you guys think it's a lost cause? I'm worried that I can't track down what blew the resistor if it isn't connected to leaking capacitors

BTW...just bought a sd1300.1 to use and should get it in a week but I doubt it'll compare with the mps2500 when it works properly. Hopefully the sd1300.1 surprises me

Well one amplifier is 500watts (the mps2500) and the other is 1200watts, so of course you'll notice a difference in output.

How do you know the resistor is burnt? Did you ohm it with a meter? Replacing a resistor is as easy as replacing a capacitor, so if you can do one you can do the other. I understand the transformer is right above it but you should have enough room to lift the resistor and install a new one (if needed, doesn't look like it by the picture provided).

The pic is kind of deceiving because of the angle I took the pic. I there would be no problem getting it out but it will be tricky to get a new one under there. I'm pretty sure it possible though.

About the power output, I was always told these mps amps are rated a lot lower than actual output. PG suggests 2 gauge wires for power and ground in the mps2500 and they say it draws up to 90A. I noticed the sd1300.1 only accepts up to 4 gauge wires so I was thinking that it might not be as powerful

Just double checked the resistor. It's a 4.7 ohm that reads 4.9 on my meter. Is it possible that the resistor just needs to be resoldered on the one side

Sorry for the newbie questions. It's been over a decade since I messed around with circuit boards

Trust me that resistor is fine, if you wish you can resolder the joint but may not be necessary.

As for the suggested wire gauge you need to keep in mind that you are comparing apples to oranges, one is a class AB amplifier and the other is a class D (more efficient) they amplify the signal differently. Check out BigDWiz dyno tests on the MS2125 you can expect the same for the MPS2500 and MAC500 (just difference impedance loads). Trust me the SD1300.1 has much more output power than the MS2125/2500, just keep in mind that one is a stereo amplifier and the other a mono so the MS/MPS has a bandwidth of 15hz-25khz while the SD is only 20hz-300hz. So you can use the MS/MPS for pretty much any application while the SD is only limited to subwoofer duty.

Ok. The rest of the mps2500 solder welds looks perfect except that one with the black burn marks. I noticed people are selling similar mps2500's for more than what I paid for the new sd1300.1 but I know they're still popular as competition cheater amps

It is really hard to tell from just one picture, but that resistor looks to me like it may have had electrolyte creep over toward it and corrode the one joint you see in your picture. Those blackish dark gray spider veins around it sure look like chemical corrosion stains to me... I would absolutely get the caps replaced and make sure the board is thoroughly cleaned...

Good Luck,
Jason

Thanks for the tip Jason. Fixing the mps will be my winter project now that I have the sd1300.1 coming. I bought a z500.4 and have been impressed how well it powers my door speakers so far so I'm sure I'll be satisfied with the sd amp for my subs. The sd is a lot smaller then the mps so I might be able to mount it in a better spot. Bonus!

Cracky, it looks to me that the solder joint is bad (lifted up/cracked) I suggest to use solder wick remove old solder and re-solder, the resistor itself "looks" good. Unfortunately you might have to remove board to see what the other side looks like the side you show looks like a cold solder joint meaning = poor connection.
It could be that the discoloration was caused by heat due to the bad connection and re-soldering just might due the trick. Just make sure if you do it to clean as best you can around the area to remove contaminants BEFORE re-soldering. 99% isopropyl and Q-tip works pretty good.

Thanks JHS. I'll try it out