Recapped my mps-2500

[interestingfellow]

And I was just looking for opinions and thoughts.
I think my iron was only 30w, and I should have used a 45. On the terminals that aren't just circle pads, i had trouble getting the solder to flow. For those pads, I let the iron heat up for 60secs or so before trying to finish that solder joint. To pull them out, I ended up doing 1 side of 1 cap, rocking it out, doing the other side, and then hit it with solder wick (which also wasn't working so well, which is also why I think my iron was to weak).

But I got it.


In process.


Dun.

[dwnrodeo]

Lot's of elecrolytic fluid under those old caps! Nicely done. Should last you quite a while now.

[ttocs]

hopefully the extra time needed to heat it will not effect any other componants. Some pieces are more sensative to heat then others and the use of a heat sink(aligatore/roach clip) is sometimes needed to help protect them. The connections do not look too bad although if I had it infront of me with a good iron I would run it across to clean them up.

[Eric D]

Hopefully you did not damage any vias, so those caps with bad vias are not really even in the circuit, or worse yet will start to arc and possibly cause additional damage. This is pretty rare though, they typically either work or don't work. Your soldering looks real good though, so that is a plus, but you may want to try getting the caps in there straighter next time.

[oldschoolfan]

It is odd that it takes more heat on one side of the caps than the other. I had the same issue, just fine tuned the heat a bit. I also checked all my connections for continuity after soldering to make sure no vias were removed or damaged without being noticed.

[interestingfellow]

Well, the requirement of more heat is becuase the - vias only have a little 5/16" circle, and the +'s are linked together on a larger piece of continuous copper trace/pad (a bigger heat sink).

I'm not too worried about the vias, as the old caps pulled out pretty easily with no indication of any lifting or so on and so forth.

Thanks ya'll, I feel better about what I did, and better about puttin some juice to this thing to check it for operation!

[freshkryp69]

do a continuity test on every cap you replaced ie: test each side of the board..traces leading to the caps, just to make sure they are still in the loop...
as far as irons go...I use a PACE desoldering/soldering station. dont even think about buy one new, check ebay for a late model iron, and you might find a killer deal in a all in one setup. the replacement parts are kinda expensive so make sure its complete when you buy it, solder/desoldering tip's, glass tube for the desolder wand, power cords, declogging round files etc..the pace's are great machines and last as long as you take care of them. .02

[interestingfellow]

FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUCK!





SHIT. Plugged it up to my van (amp/box sitting in the driveway) with 6g on ANL 200a Fuse. Some dumbass painted it, so I verified the power leads, and marked them with a sharpie. with no speakers hooked up (I didn't want a mishap to bake the amp AND the speakers), hooked up the positive, jumped the remote to the positive, and then hooked up the -. Green light turned on flashing, no other LED's were lit or flashing. I even took a video of the guts, just in case. http://s632.photobucket.com/albums/uu44 ... EO0294.mp4, cuase I figured if I fkd up, it would be an almost immediate toast.

About 4 minutes later (I was attempting to hook up my laptop to the rca's to test out the subs), my buddy starts hurriedly saying "turnitoffturnitoffturnitoff" (yes, it sounded like 1 word) and the fets opposite the power inputs started toasting 1 after the other. What the hell happened and what do I do to fix it, or should I?

Thanks guys.

[Eric D]

I take it you did not have a fuse on the power wire?

Did you have a speaker connected to it?

[interestingfellow]

200amp anl fuse by the battery

no speakers hooked up (I wanted to make sure they wouldn't get toasted in the event of a massive amp malfunction)

[Eric D]

Well there is your first problem, your amp needs like an 80A fuse tops, not 200A. So, if something were to go wrong (like it did), the 80A would hopefully blow well before the amp caught fire.

When ever you do a repair or any other modification to an amp, you need to start small, with say a 15A fuse. If you happened to have improperly installed the board back into the chassis, you may have caused a dead short on the outputs, which would cause the exact failure you have experienced. Now figuring out what is wrong is harder, as so much has been damaged. Your problem might have been very simple, and easily diagnosed if you used a 15A fuse and it blew right when you turned the amp on.

[Eric D]

Here are some other possibly questions to track this down.

Did you install the plastic sheet under the board when you put the board back in?

What did you do about the silpads under the transistors? Were any damaged from removing the transistors?

[oldschoolfan]

That sucks! Don't worry, it is still worth fixing.

[interestingfellow]

Let me start off by saying, Eric, you're right.
I know better, and should have used a way small fuse to start. I had gone with the 200a on the battery terminal becuase I intend on running another amp and a few dc jacks in the back. I had also assumed in the event of a major malfunction one of the internal 60a fuses would have blown.

Yes i placed the sheet and non conductive spacers back in place.
Yes all the thermal pads and paste were in place, good shape, not torn, and installed correctly.

So, obviously, I have to check all the SF302's, and all the resistors and diods will be easy enough, but what else should I be looking at?
Should I replace all the fets anyway (do they go bad just becuase they are old? I thought it was based on hours of use)

And then, I still have to figure out why it fried in the first place. other than a physical short, what could it have been?

[interestingfellow]

I'll strip it apart tonight, and post some more pics. On the upper left of one of the photo's it looks like the endplate is scorched behind one of my caps. If the cap failed (for whatever reason) could that have caused the fets to blow?

[Eric D]

The caps can't make the FETs fail. The FETs can fail for a variety of reasons.

One is a shorted transformer. I don't think this makes sense, as the amp has two supplies, so only one would likely fail.

Hooking the amp up backwards can blow the FETs. This usually results in them exploding though, not burning up as yours did.

Something caused a major load on the power supplies (dead short), you need to figure out what. Did you test the amp prior to doing the cap replacement to make sure it worked? I generally tell people not to do this as leaking caps will fail at any time, but maybe you tested it before posting about it here.

If you did not test it, maybe the previous owner fried a few outputs and the result was what you experienced.

[interestingfellow]

No, I didn't test it before recapping, it hadn't been used in 5 or more years, and I was afraid they had degraded to the point of immediate failure.
I had also looked carefully at the painted end plate to ensure proper polarity, and checked the user manual to make sure. I'll triple check, right now.

I think the best thing to do for now, is take close up pictures (to show, but also for later reference) and take it apart a piece at a time. I'm anxious to see the underside of the board. I'm normally not soo careless as to short traces, but shit happens; I'll check again too!

Talk to ya'll after I get it stripped apart, and thanks!

[ttocs]

ouch! Man that board looks like it got hot, hope it is still able to be saved. I often see people putting bigger fuses then needed thinking that it will make thier amp louder(not saying that is the case with you). Nothing good can come from having a bigger fuse...

[interestingfellow]

I"m totally not offended at all. I've always viewed the battery fuse for protecting against overload of the line from the equipment or if it gets pinched/knocked and grounds out.

OH, before I forget, i said the green LED was flashing. Is that signifigant (should it have been solid instead of flashing)?

I'm anxious to get it torn down.

[stipud]

Bummer dude

[oldschoolfan]

Point of information, the on the board fuses for the power supply are supposed to be 30 amps each not 60. For future reference of course.

[interestingfellow]

Hmmmmm. Just thought about somethin.

When I was disassembling the amp to recap it, I had to use the longest, thinnest filet knife I could find, and damn near pound the tip in behind the fets to get them unseated from the heat sink. Obviously, this could have damaged the fets internally, but what's the likely hood?

Then again, it ran fine for 4 minutes or so; maybe I cracked 1 or more of the fet casings letting in O2, until it finally overheated and blew/surged surrounding fets????

I dunno.
Damnit.

[Eric D]

Hmmmmm. Just thought about somethin.

When I was disassembling the amp to recap it, I had to use the longest, thinnest filet knife I could find, and damn near pound the tip in behind the fets to get them unseated from the heat sink. Obviously, this could have damaged the fets internally, but what's the likely hood?

Then again, it ran fine for 4 minutes or so; maybe I cracked 1 or more of the fet casings letting in O2, until it finally overheated and blew/surged surrounding fets????

I dunno.
Damnit.

That sounds like you broke at least one of the transistors. Pounding anything is not the way to remove these devices off the heatsink. I put a rod in the mounting hole sized for the hole. Then gently apply pressure and they pop off with little effort.

[interestingfellow]

Eric, that just makes too much sense.

I'm gonna price up all the fets, just to see. The blown fets are less than $3 each, we'll see about all the others.

If I'm gonna replace all the fets, should or can I upgrade them?

[Eric D]

Replace all the FETs in the power supply. I think you can use IRF54s, instead of IRF44s (are the 44s what were in there)?

Replace the resistors leading to those FETs. They are probably 33 ohm, or maybe 100 ohm. Get the colors off them and also check them with a DMM to be sure.

Replace all 12 of the output BJTs (bipolar junction transistors (These are not called FETs)). You will have to turn the bias pots all the way down.

If you wish you can hold off on the BJTs for now. First replace the 8 FETs, and pull the 4 fuses on the board. Those are the rail fuses, and without them, the BJTs won't get any current. You should be able to verify if the power supply works or not with these fuses out.