Phoenix Gold Phorum

So, I've repaired this MPS-2500 more times than I'd even like to admit (that would be, 3 to date, you guys have helped me all along the way and I appreciate it greatly!). The situation is, it WAS working just fine. The 4 FET's near the 2 diodes (in the power supply section) burned up on the right channel. So, I replaced these four of the 8 (again, right channel) with (I now know the wrong) MOSFETS, with a higher amp rating. It blew one 10?uf 50v cap off of the board after working for about a day. I swapped that cap out and replaced the FETS (on both sides, just because) with original spec FETS. Things worked great again. I put it in the car, and it worked for about five minutes, then gave up. Again.

This time, the symptoms are:
-Green power light
-Right channel:
-Low, very distorted output
-Both red LED's on
-Left channel:
-No output at all
-No LED's on

Anyone have any advice where to even start here?

Thanks for any advice you can offer, and thank you for your continued patience with my problems =(

http://www2.mouser.com/ProductDetail/Vi ... ME0qht2cU=

i replaced one time with these in an Original ms2250....you can also use them in place of the irfp044....

the 054 is more powerful then the 044........;

for the rest i can not help from distance.............


but i'm sure if you contact eric D , he will succesfully repair you're amp......................

I appreciate the advice, but I am reallly trying to avoid outsourcing this -- not only because I am a cheap-ass (which I will openly admit to), but also because I would like to take this opportunity to learn, and have something I have repaired on my own (albeit pretty unsuccessful to this date =/). I believe I used 55v 70A as opposed to 55v 57A the first time, when it blew a capacitor straight off the board.

So usually if I have blown FETs I replace all FETs, their gate resistors and the PWM chip. Obviously the power supply caps get replaced, along with the rail caps (only if they look like they've overheated).

If there's distortion then the first thing I look for are blown resistors or transistors. I test all resistors as some are fusible, so they won't look damaged but they measure as open loads. I then visually inspect all mini caps for evidence of overheating ( the wrapping will have moved) or leaking, and I replace them as needed.

Once that's all done, if there's still noise then it could be the phase setting (I am not qualified to tell you how to do this) or maybe something more in depth.

One thing I learned the hard way is if you change anything on the right you change to match on the left too. Knight Rider helped me out on some issues on a 2500.

If your amp has 4 fuses for the rail voltages, remove them, and then power the amp on. Make sure you have similar voltage on all 4 rails (+) and (-). If you don't then you have a power supply problem. Once you get all 4 rails equal, you can continue on to figure out what is wrong with the actual amplification circuits on each channel.

Also use a magnifying glass for looking at solder joints....

As ive become more experienced lately i am seeing more and more where factory joints have become cracked, or traces come undone, or repair by others have not have full solder connections and cause intermintent problems or not work properly.

Never thought id ever see things like that but it happens more than you think.

Okay, I am still looking at it when I have time. I have inspected a few different components, and am trying to take a bit of a scientific approach to it.

Initial testing:
**All 4 rail fuses removed from here on out, unless noted**
-Both sets of LED's are on.
-Both Clip lights are solid on
-Green LED on
-Q107 and Q206 get RIDICULOUSLY hot.
-Spec'd a few resistors (in circuit), mainly the 6 green ones attached to the leg of 2SA- and 2SC- transistors, and the big 2w .22ohm attached to the opposite legs, appeared to match on both sides.

The 2 transistors in the big cluster near what I assume are bias/offset adjustments, are what concern me -- getting so very hot. They don't appear to be shorted, so is it normal for them to get burn-your-finger-hot?

I also took a few measurements; here is what I observed.

Voltages taken across fuse terminals with fuses out (absolute value of, +/- may be wrong):
[please excuse the shitty ascii explanation]

[r] -----27.1v [caps] (this is the low-volume highly distorted channel)
[+] -----27.3v[here] <--PS
[-] -----27.0v [caps] <--caps
_ _ -----26.3v [here] (this is the channel with no LED's with fuse in)


Voltages taken across rail caps with no fuses in: (again, absolute value of)
[--amp--](30.2v) - (this is the distorted channel)
[terminals](30.2v)
[--here--](29.8v)
[--------](29.8v) - (this is the channel with no LEDS with fuse in)

I'm sorry to keep asking for all the hand-holding here; and again; thank you for your continued guidance here. Any ideas about those two transistors I mentioned? I'm pretty positive they shouldn't get that hot. They make the bottom of the board untouchably hot, pretty quick. Continuity does not reveal a shorted transistor, so there's that; at least.

Any hints on resistors to focus on? I -can- pull resistors off the board if needed; especially if I'm looking for opens instead of shorts, but I'd rather do it as little as possible if I can help it. Thanks guys!

With the fuses out, connect your DMM BLACK lead to either speaker output ground (not (-) according to the endplate, but the longer internal leads which go to the power supply, these are actually ground). Use the RED lead on the DMM to check the voltages where the fuses go. One side of the fuse goes to the power supply, the other heads off to the output sections, the side towards the power supply is of concern. You should read two positive voltages and two negative voltages. They should be similar to each other (other than 2 measure positive and 2 measure negative).

With the fuses out, nothing in the output sections should be getting hot, since there is no power to either of them.