I have a few questions...
If only one bank of power mosfets are toasts, is it absolutely necessary to replace all of them?
In the pic, the big resistors are burnts, two of them. One is missing from the pic... what are they? Are these the emitters? What caused them to burn? What else should I check? Which of the ICs is the main one?
In general what causes the power supply mosfets to go? The outputs all check out ok.
If only one bank of power mosfets are toasts, is it absolutely necessary to replace all of them?
In the pic, the big resistors are burnts, two of them. One is missing from the pic... what are they? Are these the emitters? What caused them to burn? What else should I check? Which of the ICs is the main one?
In general what causes the power supply mosfets to go? The outputs all check out ok.
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A lot of questions 
It really depends on the amp somtimes. A lot of amps use protection curcuits that are to slow to react in time if something in th e amplifier section goes wrong. You must consider in a lot of cases we ´re talking about "high throughput" manufacturing.
Cheap amps tend to "fry" the mosfets in the smps if somethng in the amp section goes wrong. That means if a power bipolar transistor dies because of overheating ther smps mosfets get fried as well cause the protection curcuit is not acting fast enough. A lot of cheap amps have that problem.
if not caused by a short in the amp section , smps mosfets are getting fried because of overheating. the problem in most cases is not that the the case temp. of the heatsink itself, in a lot of cases its just the poor manfct. quality. First thing I do when repairing an amp is resoldering the complete circuit board with standard solder while all power parts are resoldered with silver solder that has a higher melting temperature.
one problem in SMPS is high temp. --> sometimes bad solder joints cause a high resistence in the circuit. A high resistence in a switching power suppies causes mosfet transistors to switch slower. In bad conditions a DC short through the transformer coils can be the result. While a standard car audio SMPS mosfet can handle 50amps a short through the coils may allow way higher currents to flow . the fuses installed in a car amp are way to slow to get blown in time. In that case usually the whole bank of mosfets fries.
in your case , I assume its an analog amplifer, the emitter resistors are driven to their max. specification. (not unusual ) . If they are burned you know the amp has been fired a lot. think you need to make sure that there are no bad solder joints. Resolder the complete board, reinstall bad parts and the amp shoul work fine.
It really depends on the amp somtimes. A lot of amps use protection curcuits that are to slow to react in time if something in th e amplifier section goes wrong. You must consider in a lot of cases we ´re talking about "high throughput" manufacturing.
Cheap amps tend to "fry" the mosfets in the smps if somethng in the amp section goes wrong. That means if a power bipolar transistor dies because of overheating ther smps mosfets get fried as well cause the protection curcuit is not acting fast enough. A lot of cheap amps have that problem.
if not caused by a short in the amp section , smps mosfets are getting fried because of overheating. the problem in most cases is not that the the case temp. of the heatsink itself, in a lot of cases its just the poor manfct. quality. First thing I do when repairing an amp is resoldering the complete circuit board with standard solder while all power parts are resoldered with silver solder that has a higher melting temperature.
one problem in SMPS is high temp. --> sometimes bad solder joints cause a high resistence in the circuit. A high resistence in a switching power suppies causes mosfet transistors to switch slower. In bad conditions a DC short through the transformer coils can be the result. While a standard car audio SMPS mosfet can handle 50amps a short through the coils may allow way higher currents to flow . the fuses installed in a car amp are way to slow to get blown in time. In that case usually the whole bank of mosfets fries.
in your case , I assume its an analog amplifer, the emitter resistors are driven to their max. specification. (not unusual ) . If they are burned you know the amp has been fired a lot. think you need to make sure that there are no bad solder joints. Resolder the complete board, reinstall bad parts and the amp shoul work fine.
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Thanks for the replies.
thank you, this helps a lot!!
I checked diodes murs120 and the 6.8Ohm resistors - some are shorted. I will replace diodes, resistors, and ir2010. I replaced all power and output fets. The original fets were good. I checked the other diodes in the region SK2B... some of them are shorted too. My problem is that I can't find them anywhere I look. Anyone have a suggestion where I can get some, in small quantity? mouser, digikey, alliedelctronics were checked.
Also, can anyone tell me the value of R425/426.
Where can I get the rectifiers or what is a good replacement for: FRH20A15
-|<->|- This is for another amp I have -alpine mpr m500.
Both of these amps have ktd600k(npn) x2 and one ktb631K (pnp) transistors mounted to heatsink. What is their function?
Anyone out there with service manuals for any alpine mrp mXXX amps?
thank you, this helps a lot!!
I checked diodes murs120 and the 6.8Ohm resistors - some are shorted. I will replace diodes, resistors, and ir2010. I replaced all power and output fets. The original fets were good. I checked the other diodes in the region SK2B... some of them are shorted too. My problem is that I can't find them anywhere I look. Anyone have a suggestion where I can get some, in small quantity? mouser, digikey, alliedelctronics were checked.
Also, can anyone tell me the value of R425/426.
Where can I get the rectifiers or what is a good replacement for: FRH20A15
-|<->|- This is for another amp I have -alpine mpr m500.
Both of these amps have ktd600k(npn) x2 and one ktb631K (pnp) transistors mounted to heatsink. What is their function?
Anyone out there with service manuals for any alpine mrp mXXX amps?
Those diodes SK2B measured shorted ,because they connected with 3 paralleled 30 Ohms resistors.Don't need to replace them. KTD600 and KTB631 are voltage regulators.One of KTD600 provide power to IR2010S drivers,you have to measure voltage on it referenced to negative suplly rail.Should be 12-13V.Other two transistors doing +-12 V referenced to the ground.
To replace FRH20A15 (you won't find this rectifier in US) you can use mur1620 or FEP16 http://www.datasheetcatalog.org/datasheets/50/211165_DS.pdf .Replace both rectifiers,they are different ,one with common anode ,second is common catode.Those will be enough for MRP-M500 .Don't forget to put insulation pads under them,they have not insulated body.
To replace FRH20A15 (you won't find this rectifier in US) you can use mur1620 or FEP16 http://www.datasheetcatalog.org/datasheets/50/211165_DS.pdf .Replace both rectifiers,they are different ,one with common anode ,second is common catode.Those will be enough for MRP-M500 .Don't forget to put insulation pads under them,they have not insulated body.
still stuck
I'm still stuck. I replaced the diodes s120 (only one was shorted), the resistors were in spec and both of the IR2010s were replaced. Half of the fets have waveforms while the others have dc voltage, same with one of the IC drivers, one has waveform, the other just dc voltage when I look with a scope. I have been studing Perry's repair dvd for awhile now and playing with different amps, but I have a long way to go I guess. So any suggestions? Thanks for all the help!
How do I find a replacement for a broken pot for the BASS EQ? How many ohms? Or can I just wire resistors and make it non adjustable? This is for a different amp mrp500.
I'm still stuck. I replaced the diodes s120 (only one was shorted), the resistors were in spec and both of the IR2010s were replaced. Half of the fets have waveforms while the others have dc voltage, same with one of the IC drivers, one has waveform, the other just dc voltage when I look with a scope. I have been studing Perry's repair dvd for awhile now and playing with different amps, but I have a long way to go I guess. So any suggestions? Thanks for all the help!
How do I find a replacement for a broken pot for the BASS EQ? How many ohms? Or can I just wire resistors and make it non adjustable? This is for a different amp mrp500.
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