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Old 19th April 2012, 09:14 AM   #1
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
Default Repairing Alpine MRV-1507

Hi there!

I got a blown Alpine MRV-1507 amplifier from a friend of mine.
like he told me, the amp has worked properly and in the next moment it smelled burned and has stopped working.

after disassembling I found out that the IRFZ48N transistors was blown

Click the image to open in full size.

Click the image to open in full size.

After checking the related IRF540s and IRF9540s, I found out that all IRF540 are nearly shorted (only 2ohms between leg 2 and 3)
(the IRF9540 does not)

I have ordered all of the related IRFZ48N and IRF540N transistors and will replace them tomorrow.

I have also found out that in the lower right corner the trace between J122 and J603 is broken and charred.

Click the image to open in full size.

Click the image to open in full size.

Can anyone tell me what may cause them to fail?
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Old 19th April 2012, 09:30 AM   #2
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The shorted output transistors caused the power supply to fail. The excessive current from the failure of the power supply FETs likely caused the trace to burn.
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Old 19th April 2012, 10:19 AM   #3
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
And what caused the output transistors to fail?
overheating, some other defective components of this amp or bad speakers?
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Old 19th April 2012, 11:51 AM   #4
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It could have been a random failure, attempting to drive an unsafe load or the failure of another component.
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Old 20th April 2012, 03:46 PM   #5
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
OK, I have replaced all of the related IRFZ48N and IRF540N transistors.
I have already read through this thread to find out how to check if everything works properly:
Help fixing Alpine MRV 1507

I have adjusted the VR601 and VR601 (with VR401 and VR402 set fully counter clockwise)

but how should I adjust the VR401 and VR402?
should I leave them full couter clockwise?
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Old 20th April 2012, 04:05 PM   #6
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
Quote:
Originally Posted by Perry Babin View Post
You now need to set the bias. The two test points indicate the level of bias. With the bias pots fully counter-clockwise, it's expected to read 0.000v DC. You stated that the amp was overheating. The test across the bias test points was to see if there was too much current flowing through the outputs at idle.

Connect the meter across the test points (preferably with test clips of some sort) and slowly turn the bias pot until the voltage reaches 0.001v DC. Do this with no load and no signal. Let the amp idle and confirm that the bias remains constant. If it drifts up, readjust it until it remains at about 0.001v DC after several minutes. Do the same to the other channel. Have a 10-15 amp fuse in the B+ line while doing this.
I found what I was searching for
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