Phoenix Gold MPS-2500 Repair & Schematics Needed - diyAudio
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Old 30th August 2015, 08:51 AM   #1
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Join Date: Apr 2015
Default Phoenix Gold MPS-2500 Repair Help?

Well, here is the second of my failure-forays. I have (had, in a way, now) a Phoenix Gold MPS-2500. It is a beautiful amp, and I ****** it up. Now I want to cheat death for this poor little guy. Here's the story.

I bought this maybe 6 months back on eBay. It came in pretty goofy condition -- someone had clearly already done something to it (I will be posting pictures, in hopes that you can tell me what exactly was done; I took some when I took this apart for the first time to do the obligatory capacitor replacement). While I was in there, I had to replace the wiring to the RCA jacks. This is I believe revision B (or maybe A, whichever used the old smaller connectors). I have an MPS-2125 bus bar/terminals/end cover set, that I was using for a while, but I switched back because I could not access the gain control like that; otherwise everything was fine. (this is irrelevant though). Anyhow, a few months ago, I was simply sitting in a parking lot, not listening to anything but radio on, when I smelt The Bad Smell -- the smell that means GTFO your car and flip the breaker, don't wait for the 150A fuse to give out. Sure enough, my amp had turned my custom plexiglass cover a nice nasty soot color, and melted 2 of one channel's transistors nearest the caps. Anyways, I figured that is weird, and simply replaced the transistors. However, I purchased instead of the original (can't remember 50 or 55v), 57A transistors, some (matching 50 or 55v, can't remember), 70A transistors, at the recommendation for a good substitute from the sales rep (B&D Enterprises, they're close and I get a lot of my parts there).

I replaced the 4 transistors on the damaged side (the channel that is on your right-hand side, if you were looking at the visible side of the circuit board with the bottom off and the capacitors nearest you), and it worked fine after that... For about two days. I noticed it started to sound 'distorted' about 5 seconds before it died completely. When I went to the trunk to see where my bass went, and I found the red (protect) light on. I took the amp out, and inspected, to find no burnt looking anything, but a blown off (literally, off the board) 50v 10uf capacitor (I believe it was capacitor C221, the one labelled 4.7uf 100v on a MS-2125 schematics diagram, which is not the same as this amp I know -- the capacitor im a matching spot on the other channel is also a 50v 10uf cap) and a blown fuse (the one closer to the edge of the board of the two on that channel). I replaced this capacitor, and fuse, and now get nothing -- no power light, no protect light, nothing.

So, how bad could I have ****** it up, I want to ask (any ideas)? Did my sale's rep's recommendation and my dumb decision to not look further into that, cause this issue? Any clue where to look from here? Also, bonus question -- what are these modifications to this amp? Are these repairs, or some sort of modification? Note: pictures all from before amp blew up.

Last question. Anyone have the schematics diagram of an MPS-2500, preferably early revision? I have the schematics of a MS-2125 if anyone needs those. Can I attach that file here, or is that not allowed? Can email upon request, if that's not okay. Repair materials should be accessible to all, in my opinion.

Last edited by laughatthemall; 31st August 2015 at 03:47 AM.
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Old 31st August 2015, 03:46 AM   #2
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Join Date: Apr 2015
Double post peril! I forgot to post the pictures :P

I couldn't find the original pictures I had taken, so I took some of the board in current state. I have included 'orientation numbers' to help you get an idea of where the zoomed in pictures are. Any idea what these components added on are for? Any way I can revert this back to 'stock'? Thanks!

Pictures:
http://i.imgur.com/ROFzGBN.jpg
http://i.imgur.com/6bsO8s0.jpg
http://i.imgur.com/vDLazgH.jpg
http://i.imgur.com/PBxmM4V.jpg
http://i.imgur.com/3CQEyDo.jpg
http://i.imgur.com/zXKLJcj.jpg
http://i.imgur.com/1BmZnpW.jpg
http://i.imgur.com/ZBHCHva.jpg
http://i.imgur.com/usDWqEf.jpg
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Old 31st August 2015, 04:01 AM   #3
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Join Date: Nov 2003
Location: Louisiana
I have nothing on this amp. I don't know if the people on the following forum can help with repairing it but they may be able to tell you if the mods are factory or not.
Phoenix Gold Phorum • Index page
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Old 31st August 2015, 04:46 AM   #4
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Join Date: Apr 2015
I thought that place was shut down o.o Last time I tried to go there I got a big old nooope for its' existence. Ah well, I'm glad to say it didn't! Thanks for reminding me of them :P
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Old 31st August 2015, 06:39 PM   #5
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Join Date: Dec 2005
Location: Northern California
Those mods are common place for the MPS2500. The 2500 used the same PC board as the 2125 and 2250, but the drive considerations for the MPS2500 are considerably different due to its low ohm capabilities.
Thus the gain difference of the two resistors on the bottom of the board and the bias control differences and the thermal stability requirements that all required the add-on of those components to make the amp stable and reliable at 1/2 ohm mono loads it was expected to drive back then.

The early designed use different outputs, yours is a typical production run design, and not un-common to what all production units looked like. I have the two documents for the original and the production unit. The production units had mods to compensate for bias, thermal tracking, and low ohm operational needs that needed to be addressed to get the amp to meet its application expectations and requirements...Except for the special low ohm mods and it power supply toroids and main caps its a MS2125/2250 variant....

Hope this helps some
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Old 4th December 2015, 09:07 AM   #6
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Join Date: Apr 2015
Okay, it's been a while, but I have an update. I finally got back to this amp, and worked on it. This amp, I am pleased to say, is now fixed and working again! I ordered parts, replaced all the gate resistors against my original thought of 'no need', and replaced PWM's, as well as checked for any cold solder joints on the transistors and replaced a few other resistors... It is working perfectly now, so that is nice I just wanted to 'close up loose ends' here, and say thank you all for your help!
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