MS-2125 Help. Beyond Repair????

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Pheadrus
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MS-2125 Help. Beyond Repair????

Post by Pheadrus »

I'm new to the site and amp repair in general. I'm looking for some advice on a MS-2125 I recently picked up.

I have a bunch of old school MTX Thunder series amps(2300, 4320, 4160, etc.) and some need repair so I was looking for cheap used amps to learn on. I got lucky and bought a MS-2125, a Kenwood KAC-943, a Clarion APX320.2, Kenwood 12 sub and box, and a Clarion ProAudio 12 sub with box all for $80CND/$60US. The Clarion amp and the Kenwood sub both work so I feel that was worth the $80 I spent on everything. The guy I got them from said he was given the MS from a friend and never hooked it up. I pulled the back off and found 3-4 burnt Mosfet's and the ground bar had burning on it as well. The caps don't seem to have leaked but I haven't slid a piece of paper under the caps to check for fluid. The board says it's a Rev. C - I. Can the amp be fixed or is it too far gone?

I have a Weller WES51, an old school big Weller, and a solder sucker as well.

Thanks for any advice and knowledge.
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Pheadrus
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

More pics.
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Pheadrus
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

Other than 3 of the 4 Mosfets being burned and the ground bar, I couldn't find any other damage. The SF302 and SF302A don't look damaged but I defer to the experts here for advice. I essentially got the amp for free, so I don't mind putting some money into it if it can be fixed.
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Eric D
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Re: MS-2125 Help. Beyond Repair????

Post by Eric D »

That amp is well worth fixing. The repairs should not be too difficult.

PG boards of this type are easily damaged with too much heat from your soldering iron, so keep that in mind.

You will need to replace the 12 power supply input capacitors, as yours are leaking.

You will also probably have to replace the gate resistors for the MOSFETs, and maybe the SG2525 (or SG3535) PWM controller which signals the MOSFETs. Sometimes it dies when the MOSFETs do.
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Pheadrus
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

Thanks for the input Eric. I'm glad to hear it can be saved. I'm a huge fan of old school car audio and on a tight budget so fixing the amp myself would be awesome.

I'm curious, I couldn't see any fluid by the caps. How can you tell mine are leaking from the pics? Or are you just assuming that because they're the factory caps? As I said in my first post, I'm new to repair.

Should I upgrade to 064N's for low ohm performance or is there something better available? Especially if the gate resistors have to get changed anyway? I'm guessing all the 044's and gate resistors on both channels would have to be upgraded correct? If I stuck with 044's, I assume only the four would have to be changed but would the gate resistors on both channels have to be replaced if the two on the blown side are upgraded?

Can you or any members suggest the best site for the parts? Also what would be the current part #'s for the gate resistors, fets, and caps? For example, what would be the best caps to get? Should the rail caps be done as well? I'd prefer to upgrade any parts possible for longevity and better performance while I have it apart like the longer life Panasonic caps if the cost difference isn't huge.

Lastly, what do you think caused the amp to blow considering the damage? Why did the ground bar over heat? Should I remove the ground bar, clean off the melted coating, and then clear coat it? Or should I just leave it?
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Re: MS-2125 Help. Beyond Repair????

Post by ttocs »

that is just the insulation on the bar that is burned but if you want one with out burns on it I have an extra
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Eric D
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Re: MS-2125 Help. Beyond Repair????

Post by Eric D »

-I can tell your caps are leaking by the little white sticker on the top of one of them. That sticker means they are from the bad batch that leaks. When you remove them, you will find the fluid built up between the board and the rubber end, which you cannot get a piece of paper under to test.

-I would stick with 044N's as the OEM solution is plenty good for the ratings of the amplifier. These amps are true dual mono, so you would only have to repair the one bad side (assuming the other side is still good).

-I buy most of my parts from http://www.digikey.com

-I don't have the parts values off hand for the resistors, but you can measure the other side to see what they are (and look at the colors to match up with your measurements). Here are the input supply caps I use...

http://www.digikey.com/product-detail/e ... -ND/589284

...some people prefer other brands.

-I would not replace the rail caps. They are difficult to replace without damaging the board, and you would not gain any performance upgrading them.

-I think the user of that amp drove it way to hard into too low of an impedance load. It then blew some fuses, so they bypassed them, and that is why the buss bars were able to overheat so bad as to burn their coating. It takes a ton of current to get the bars that hot. Another possibility is the set screws on the buss bar were loose and stared to "arc out", causing a ton of heat to form there. Is the plastic power input terminal on the amplifier melted at all?

Here is some additional info which may be of help...

http://www.soundbuggy.com/Eric/Car%20Au ... index.html
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Pheadrus
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

ttocs wrote:that is just the insulation on the bar that is burned but if you want one with out burns on it I have an extra

I sent you a pm about the Buss bar. If I can afford it, I'll take it. Let me know what you need for it.
Thanks.
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

How do I measure the transistors correctly? Each side has 044N's but they have different smaller numbers below the IRFP044 on each one. What's the Panasonic number for the caps? From reading, it seems they have a much longer life. What would be the replacement parts for the SF302 and SF302A?

Lastly, what cleans off the soot from the board and back plate the best?

Thanks to everyone for there knowledge and time. I'm really enjoying learning about the PG amps and amp repair in general.
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Eric D
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Re: MS-2125 Help. Beyond Repair????

Post by Eric D »

-https://www.google.com/search?num=20&si ... re+tr&gs_l

-You probably don't have to replace the SF302 and SF302A, they care pretty tough and seldom fail.

-I use lacquer thinner and a Q-tip to remove soot. You have to be careful though, it will remove the writing on components (like capacitors) instantly.
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Pheadrus
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

Eric D wrote:That amp is well worth fixing. The repairs should not be too difficult.

PG boards of this type are easily damaged with too much heat from your soldering iron, so keep that in mind.

You will need to replace the 12 power supply input capacitors, as yours are leaking.

You will also probably have to replace the gate resistors for the MOSFETs, and maybe the SG2525 (or SG3535) PWM controller which signals the MOSFETs. Sometimes it dies when the MOSFETs do.
Sorry for being repetitive but I just want to be sure of what I'm ordering being new to amp repair.

By gate resistors, you mean the 3 burned resistors beside the SF302 and SF302A correct?

How do I tell if I need a SG2525 or SG3535?

So in total, I would need 12 Nichicon UHE1C562MHD6 caps, a SG2525 or SG3535, and the 4 gate resistors?

Whats the best sil-pad and flux to use? I already have Kester 44 60/40 solder.

What can I use on the back plate to remove the soot? Iso alcohol? I'm guessing the laquer thinner would take the paint off with the soot.

By the way Eric, when I pulled the cover, all the tube fuses were intact. Do you still think they were blown and bypassed? I figure that if someone took the amp apart and saw the damaged resistors, etc., they wouldn't bother changing the tube fuses and put it back together.
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

While researching and trying to learn as much as possible, I found vwdude's list of parts in another thread. He recommends Nichicon UHE1C822MHD's for the caps instead of the Nichicon UHE1C562MHD6's. The only difference I see in specs are the MHD's are 8200µF compared to the HD6's 5600µF. Besides being rated higher, the MHD's are also a little cheaper. So should I put MHD's in or am I missing something?

In that same thread, Jacampb2 says the PWM controller is a SG3525. I went on Digikey and there are alot of options. How do I know which one is correct? Do I just look at the one on my board or do I measure something?

I only found this resistor(part #IRFP044NPBF-ND) for the IRFP044's on Digikey

http://www.digikey.com/product-detail/e ... -ND/811533

The rest say they're obsolete.
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Re: MS-2125 Help. Beyond Repair????

Post by ttocs »

lots of repairs are keeping our lead techs busy lately.
what else can I say I am a grumpy asshole most of the time.
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Re: MS-2125 Help. Beyond Repair????

Post by RayBuck »

Sure has its awesome
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Re: MS-2125 Help. Beyond Repair????

Post by Eric D »

-I added a photo where I circle the gate resistors.

-Look at the PWM controller. It will say SG2525 or SG3525 on the top of it. Buy the same as the one for the other side.

-You need the 12 caps, the gate resistors, the 4 MOSFETs, and possibly a PWM controller.

-I think these pads would work, but you need to get some other opinions from other members...

http://www.digikey.com/product-detail/e ... -ND/307800

-Your solder has the flux in it already.

-The back plate of the amp is powder coated, and is really tough. Yes, lacquer thinner will remove the coating, but it would take a long soak to do that. I keep a roll of toilet paper on my bench. I pull off one square, fold it in half, dip it in thinner and quickly wipe the soot off. I think you will get the hang of it quickly. You can try other cleaners, but I have yet to find something which will remove it well, and not damage the underlying coating.

-What value are the fuses in it? They should blow well before the buss bars cook, so something had to be wrong with the install.

-I would stick with the 5,600uF caps, only because they are OEM height. The 8,200uF caps are too tall in my opinion. You are welcome to use either, but I try to keep everything as close to OEM dimension as I can, it is just my personal preference.

-I think this SG3525 would work...

http://www.digikey.com/product-detail/e ... -ND/599613

Before you buy anything you need to do some more work. First, remove the board, then clean the board, heatsink, and cover. Remove the 4 bad MOSFETs, the 4 gate resistors, and the 12 power supply caps. Clean up the pads where they go so they can accept the new parts (use solder wick to clean). Do you have a DMM then? Does it happen to measure frequency? Is it TrueRMS? You can power up the board on a test bench (with certain restrictions we can help you with at that point), and test the PWM controller to see if it is dead or not. You can also test the other side at the same time to verify its function.
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Re: MS-2125 Help. Beyond Repair????

Post by vwdude »

You can use either cap. I like the 8200 when it fits, and they do fit in these amps. I would like to see Eric's thoughts on this though. (Ok now I see it, we posted at the same time)

The gate resistors are the through home axial resistors that are just in front of each mosfet. You can follow the lead from one leg of the mosfet to its gate resistor.

For the pwm controller, you can use either a 2525, 3535, or 3525. I prefer to order what's already on the amp to keep it original. I also like to use Fairchild brand if it's available. Whenever I replace these I do the pair, and I install sockets for easy replacement in the future.

When you replace the mosfets, you will have the board out. Reinstall it and screw the board itself down the heat sink to properly line the new mosfets up with their gold down screw holes. Otherwise they won't line up when you go to reinstall the board.
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Eric D
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Re: MS-2125 Help. Beyond Repair????

Post by Eric D »

I also suggest you look around the forum for information on how to remove the transistors from the heatsink. I think either I or someone else made a write-up on this. I don't remember where it is, but you should be able to find it. If you do it wrong, this is difficult. If you do it right, it is easy to do.
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Pheadrus
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Re: MS-2125 Help. Beyond Repair????

Post by Pheadrus »

Thanks a lot guys. I've been reading all the threads I can find and watching youtube videos. I'm really enjoying learning and appreciate all the advice from members. I love the custom build threads members have on here as well. The only problem is I'm getting addicted to PG amps!! lol

I have about 5 MTX Thunder 2300's that need repair as well so I'm in this for the long haul.

I didn't want to take the amp apart until I had the parts but I'll start to disassemble it this week and update you guys. I have a few multi-meters. Some old school anologs and a couple of digital models. I'll have to check the specs.
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Re: MS-2125 Help. Beyond Repair????

Post by Virtue »

Just looking at old posts. In the picture on the burnt side. The SPF 302a and SPF 302 diodes both have the same + symbol on the front. One should be + and the other should be -... kind of weird??? Was this amp repaired before?
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