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Discussion Starter #1
Im trying to fix an amp
The power supply has 4 transistors that need to be replaced. One was burnt. and it was dangling by a leg.

There are 2 others on the opposite side of these that are fine

The part numbers I got off the 4 are
NX
psmn015
100p
pem 0827
7842



And Im not to great at fixing amps but do know a little bit.
Im great with a soldering iron. I have a multimeter.
And I have the mental capacity to learn.

The amp blows fuses when it powers up.
I asked a tech that said the power supply is out. Sure enough its burnt.
It also looks like the left side of the amp, ( left channels ) were replaced. I had to redo the soldering. They all seem fine.

So, Any tips and links to the product I need would be much appreciated.
Its for a really nice expensive amp I got from here.
Id like to try fixing it before I pay $225 to have someone else do it.
It doesnt look bad. The worst part is the terrible soldering job , which I think shorted out the legs on the transistors in the power supply.
Looks like a 5yo tried to solder everything.
 

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I think those are some off brand generic replacement parts.Are these in the power supply?
 

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Yes they all have to match.The most common power supply mosfet is the irfz44.
Are these the to220 case or the larger to247?
How many watts is the amp?What model is it?
 
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Discussion Starter #5
Yes they all have to match.The most common power supply mosfet is the irfz44.
Are these the to220 case or the larger to247?
How many watts is the amp?What model is it?
The amp is a MMats SMT4090. Its a 90 wattx4 amp.
The 4 transistors are To 220's

About the resistor. Should I replace it with the same surface mount type? Or can I use a 10 ohm quarter watt? If so then I can go ahead and replace all 4 surface mount resistors with 10 ohm quarter watts. Is that ok? Cause its gonna be tough soldering them little things in place.

Thanks for the help
 
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Discussion Starter #6
THIS is what I found about the 4 transistors that were in the amp.
I think these will work.
From what I can see, the soldering job was the reason they burnt. The legs were slightly soldered together.
After they burnt, maybe the small resistor got too hot and changed value.
 

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I doubt you be able to get by just replacing the mosfets and the resistors.
The drivers for the mosfets and possibly the PWM IC is also damaged.
Trace back from the 10 ohm resistors and see what drives them.look for a 16 pin chip with # like tl494-594 ,sg3525.that is the PWM IC.and it might drive 2 or 4 small transistors.
 
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Discussion Starter #8
I doubt you be able to get by just replacing the mosfets and the resistors.
The drivers for the mosfets and possibly the PWM IC is also damaged.
Trace back from the 10 ohm resistors and see what drives them.look for a 16 pin chip with # like tl494-594 ,sg3525.that is the PWM IC.and it might drive 2 or 4 small transistors.
Theres an sg3525ap and 2 small transistors next to it.
 

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I would replace them before you power the amp or the mosfets will blow again.
Have you checked the output transistors in all 4 channels for shorts?
Do you have a scope?
 
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Discussion Starter #10
I would replace them before you power the amp or the mosfets will blow again.
Have you checked the output transistors in all 4 channels for shorts?
Do you have a scope?
no scope. i just compared the transistors using a diode check on the dmm and they are all the same.
and
i didnt find any shorts

looks like the driver and small transistors were not replaced. this may also be why the amp burned up again.

wondering why they replaced all the left channel outputs?

they all measure good.

as well as the e factory ones that werent replaced.
 

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Im trying to fix an amp
The power supply has 4 transistors that need to be replaced. One was burnt. and it was dangling by a leg.

There are 2 others on the opposite side of these that are fine

The part numbers I got off the 4 are
NX
psmn015
100p
pem 0827
7842



And Im not to great at fixing amps but do know a little bit.
Im great with a soldering iron. I have a multimeter.
And I have the mental capacity to learn.

The amp blows fuses when it powers up.
I asked a tech that said the power supply is out. Sure enough its burnt.
It also looks like the left side of the amp, ( left channels ) were replaced. I had to redo the soldering. They all seem fine.

So, Any tips and links to the product I need would be much appreciated.
Its for a really nice expensive amp I got from here.
Id like to try fixing it before I pay $225 to have someone else do it.
It doesnt look bad. The worst part is the terrible soldering job , which I think shorted out the legs on the transistors in the power supply.
Looks like a 5yo tried to solder everything.
$225!!!

Man, that's ridiculous!

IRF3205 is a good replacement. Don't need the high voltage in the primary side.
 
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Discussion Starter #12
$225!!!

Man, that's ridiculous!

QUOTE]

Yea that is stupid high.
That is the price MMas charges. Its a flate rate for all there amps. Old or new.
Man I can get a new amp for that !!!
I got another quote from AMp Medics but it was almost the same and the dude seemed like a a$$.
Im willing to pay but not a arm and a leg. And pay to someone that at least is willing to tell me a little bit about the problem and how it was fixed so I can learn a little bit.
Thanks for the help.
 
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Discussion Starter #13 (Edited)
Ok. So I retested the output transistors. What i get this time is
some are measuring 1.2volts and most are measuring .6volts.
Its cause some are IRF540 and some are IRF9540

Maybe I should send it in. LOL

Man i feel like Im gettin in over my head here. LOL
But its fun :)
 

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Use your DMM set to Ohms and find out if Pin #11 or Pin #14 of the SG3525 is directly connected to one side of the FET gate resistors on the burned up side.

If either of them are, I would replace the SG3525.

If either of them are not, you will need to find all of the FET drivers and check them. There is probably more than two of them. Follow the traces from pins 11 & 14 or trace back from the FET gate resistors.
 
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Discussion Starter #16
I decided to send it to MMats
I have no idea why but they decided to fix it for $150
I think the guy that answers the phones there isnt too swift on the pricing.
Maybe the amp models are on a scale and mine fell into the $150 range. IDK
I sent it off.
Its over my head.
When I get it back it should be all nice and ready to Jam. Like new is what they said.
And that price is including shipping back to me.
So, for a super rare amp , with high SQ , I went ahead and paid the $150. Thats the usual and I was already willing to pay that anyway.
Even if I decide to resell later, the amp will have great value.
 

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I decided to send it to MMats
I have no idea why but they decided to fix it for $150
I think the guy that answers the phones there isnt too swift on the pricing.
Maybe the amp models are on a scale and mine fell into the $150 range. IDK
I sent it off.
Its over my head.
When I get it back it should be all nice and ready to Jam. Like new is what they said.
And that price is including shipping back to me.
So, for a super rare amp , with high SQ , I went ahead and paid the $150. Thats the usual and I was already willing to pay that anyway.
Even if I decide to resell later, the amp will have great value.
Wow. It would have been $85 plus parts from me. ;)

Oh well...next time, huh?
 
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Discussion Starter #20
Got the amp back today. This thing sounds really good. Id have to say it sounds more neutral than any amp Ive heard. Not too bright not to warm not to sweet or mellow. Ive heard all those kinds of amps. It also isnt over powering or even fatiguing. Its just an amplifier that amplifies. LOL
I think Im gonna keep this one. Ill be on the look out for another MMats amp for bass.
This amp was worth the money to fix.
 
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