Broken Soundstream MC Amps

mitchyz250f · 13th March 2008, 01:13 PM

I have two non-functioning Soundstream MC amps. I don't know the history on either amp.

MC120
No lights when powered up.
Power supply setup is 13.0 volts.
On startup after about two seconds, the voltage 7.3 volts and the amp draw is 9.0.

MC140
No lights when powered up.
Power supply setup is 13.0 volts.
On startup after about two seconds, the voltage 13 volts and the amp draw is 0.0.

Any help will be appreciated.

jol50 · 13th March 2008, 01:50 PM

Pop the cover and take an ohm meter, test all the transistors on the heatsink. I do the outside legs, any shorted will tell you a problem is there. There may be two that are shorted, those would be rectifiers and go to rail caps. If the rest test high ohms then check outside to center legs. Look closely for any soot or burns, melted solders, etc. If you are not sure what to look for go to Perry's site and check it out: http://www.bcae1.com/ Wild guess is the one that is dead has a power supply fault maybe turn on circuit, the other one output section is damaged. Take the one that runs and check voltage at speaker leads when you fire it up, briefly. Check each channel for DC voltage and bridged channel. That might give an idea what is wrong. I have not worked on one of those. If you have lights that do not light you may have a secondary power issue, the power for input section.

Perry Babin · 13th March 2008, 01:56 PM

The MC120 probably has shorted output transistors.

I'm assuming that the MC140 never draws any current. If that's the case, there could be several faults. You need to confirm that you're getting ~12v to the power supply FETs and to the power supply control IC (SG3524?).

mitchyz250f · 13th March 2008, 02:45 PM

More info:

MC120
No lights when powered up.
Power supply setup is 13.0 volts.
On startup after about two seconds, the voltage 7.3 volts and the amp draw is 9.0.

The previous owner had had replaced one of the 3 amp fuses with a 10 amp and run that side in mono. The two dark blue 2200uf25v caps on that side are leaking. The main fuse was changed to 25 amp from what I think should be a 20 amp.

MC140
No lights when powered up.
Power supply setup is 13.0 volts.
On startup after about two seconds, the voltage 13 volts and the amp draw is 0.0.

Couldn't see anything wrong. Everything looked brand new inside.

Perry Babin · 13th March 2008, 03:16 PM

The caps need to be replaced. While you have them out, THOROUGHLY clean the board and check for open traces. The electrolyte is corrosive and will eat through the copper foil. An open trace can cause excessive current draw. It's also possible that one of the caps is shorted.

Did you check for shorted rectifiers or shorted outputs?

Did you check for supply voltage on the MC140?

mitchyz250f · 13th March 2008, 04:02 PM

Thanks Perry. I will look into those items you mentioned tonight. I forgot to mention the MC140 looked perfect inside but did have a blown internal three amp fuse.

mitchyz250f · 26th July 2008, 04:46 PM

Just fixed the 140. There was a break in the trace from the ground wire.

Hopefully, I will get to work on the 120 soon.

13th March 2008, 01:13 PM	#1
mitchyz250f diyAudio Member Join Date: Nov 2004 Location: ga	Broken Soundstream MC Amps I have two non-functioning Soundstream MC amps. I don't know the history on either amp. MC120 No lights when powered up. Power supply setup is 13.0 volts. On startup after about two seconds, the voltage 7.3 volts and the amp draw is 9.0. MC140 No lights when powered up. Power supply setup is 13.0 volts. On startup after about two seconds, the voltage 13 volts and the amp draw is 0.0. Any help will be appreciated.

13th March 2008, 01:56 PM	#3
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The MC120 probably has shorted output transistors. I'm assuming that the MC140 never draws any current. If that's the case, there could be several faults. You need to confirm that you're getting ~12v to the power supply FETs and to the power supply control IC (SG3524?). __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

13th March 2008, 03:16 PM	#5
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The caps need to be replaced. While you have them out, THOROUGHLY clean the board and check for open traces. The electrolyte is corrosive and will eat through the copper foil. An open trace can cause excessive current draw. It's also possible that one of the caps is shorted. Did you check for shorted rectifiers or shorted outputs? Did you check for supply voltage on the MC140? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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13th March 2008, 01:50 PM	#2
jol50 diyAudio Member Join Date: Nov 2007	Pop the cover and take an ohm meter, test all the transistors on the heatsink. I do the outside legs, any shorted will tell you a problem is there. There may be two that are shorted, those would be rectifiers and go to rail caps. If the rest test high ohms then check outside to center legs. Look closely for any soot or burns, melted solders, etc. If you are not sure what to look for go to Perry's site and check it out: http://www.bcae1.com/ Wild guess is the one that is dead has a power supply fault maybe turn on circuit, the other one output section is damaged. Take the one that runs and check voltage at speaker leads when you fire it up, briefly. Check each channel for DC voltage and bridged channel. That might give an idea what is wrong. I have not worked on one of those. If you have lights that do not light you may have a secondary power issue, the power for input section.

13th March 2008, 02:45 PM	#4
mitchyz250f diyAudio Member Join Date: Nov 2004 Location: ga	More info: MC120 No lights when powered up. Power supply setup is 13.0 volts. On startup after about two seconds, the voltage 7.3 volts and the amp draw is 9.0. The previous owner had had replaced one of the 3 amp fuses with a 10 amp and run that side in mono. The two dark blue 2200uf25v caps on that side are leaking. The main fuse was changed to 25 amp from what I think should be a 20 amp. MC140 No lights when powered up. Power supply setup is 13.0 volts. On startup after about two seconds, the voltage 13 volts and the amp draw is 0.0. Couldn't see anything wrong. Everything looked brand new inside.

13th March 2008, 04:02 PM	#6
mitchyz250f diyAudio Member Join Date: Nov 2004 Location: ga	Thanks Perry. I will look into those items you mentioned tonight. I forgot to mention the MC140 looked perfect inside but did have a blown internal three amp fuse.

26th July 2008, 04:46 PM	#7
mitchyz250f diyAudio Member Join Date: Nov 2004 Location: ga	Just fixed the 140. There was a break in the trace from the ground wire. Hopefully, I will get to work on the 120 soon.

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