Possibly Fried Alpine MRV-F352 5 channel Car Amplifier - diyAudio
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Old 24th February 2009, 11:37 PM   #1
lickwid is offline lickwid  United States
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Unhappy Possibly Fried Alpine MRV-F352 5 channel Car Amplifier

So I am a relatively novice when it comes to installing car audio. Anyway, I've hooked up my 9 year old Alpine amplifier, and it seems to be malfunctioning.

The first problem is that the power light never fully shuts off. When the key is out of the ignition, the power is about 50% full brightness. When the key is turned to ON, it fully brightens. I've checked and double checked the blue remote on wire, and it's hooked up as it should be. What could be causing this?

The second problem, and the far worse problem, is that the 5th channel barely outputs any power to my sub. The other 4 channels work fine for my component speakers and coaxials. After deciding to open up the amp, I noticed at least one transistor that seems to have fried. What could have caused this?

Is it worth it to even try to repair it, or should I just toss it and buy a new amp? Thank you for your time.
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Old 25th February 2009, 01:57 AM   #2
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Can you post a photo of the amplifier's internal components?
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Old 25th February 2009, 03:29 PM   #3
jol50 is offline jol50  United States
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They are fairly good amps IMO. The sub channel is a bridged channel in the one I have but think it is a 353 model. Look up the manual for it, I found one for mine free. Anyway, the manual says 4 ohms on the sub channel not 2 and that is typical for bridged. If someone ran it at 2 that may have blown it I am not at all sure if they can handle 2 ohms on sub....they can on highs like a normal 4ch. In mine the sub is its own two bridged channels and has its own power supply, is easy to see. Yours could be different, but many of the mrv are similar designs. I'm not sure if I have photos of mine.
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Old 25th February 2009, 04:16 PM   #4
lickwid is offline lickwid  United States
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I will try to take it apart again and take a photo of the entire board and some close ups of the portion that looks fried. The pins were even bent back from the transistor chip itself.

Hopefully I make some sense, I'm a novice when it comes to circuit boards.
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Old 25th February 2009, 04:27 PM   #5
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I fixed an MRV-F407 (4 channel) Alpine amp with similar issues. The pair of MOSFETS in the output stage for one channel had failed. Replaced them and it works very nicely. They are good amps and worth saving IMHO.

The fact that some channels work siggests the power supply is working fine.

What have you conencted the remote turn-on line to? could it be that it's not dropping completely to zero volts with key off?

Kevin
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Old 25th February 2009, 05:08 PM   #6
jol50 is offline jol50  United States
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You can always take a meter on ohms and trace the speaker terminal to the output on the sink. If the sub channel is bridged you will have two pair of output transistors, one pair will likely have the right leg connected to one sub speaker terminal and other pair the other terminal. An unbridged channel will have one side of a speaker common and other to a pair (more than a pair in larger amps). Ignore the + and - for this purpose unless it is an old unbridgeable amp.

Ampguts has no pics of a 5ch I could find, the 757 is a tripath and much different.
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Old 25th February 2009, 06:16 PM   #7
lickwid is offline lickwid  United States
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I've only connected the remote on lead to the blue/white wire that comes from the back of my Head Unit. I was having similar problems with my old setup, so I think that remote on issue is old. I just never messed with it before and was just going to try to fix it in my new setup. I guess the problem might be an internal one.

Thanks for all the suggestions so far. I will take some detailed photos and post them on here by the weekend and hopefully we can get somewhere with fixing this thing. I definitely enjoy taking electronics apart and fixing them. I just do not have a whole lot of experience, so I will probably need some "hand-holding" once I get those photos up here.

My background is basic soldering of wires for modifications onto mainboards, but never really replacing entire chips, transistors, etc.

If I don't make any sense, it's because I'm an idiot....
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Old 25th February 2009, 09:33 PM   #8
jol50 is offline jol50  United States
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Just need to find the broken parts and replace, not that bad, but hard to do when we can't see it. If I have time I will dig mine out it is likely the same but I can't find any photos must not have taken any.

Keep at it and you will only be half an idiot like me It can be fun at times. I've done enough alpines now to forget how many, but I like them for some reason.
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Old 26th February 2009, 02:18 PM   #9
lickwid is offline lickwid  United States
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Ok, I will try to get some photos up here in the next couple of days. My digital camera broke, so I'll have to borrow a friend's. Thank you. I may actually be able to fix it. We'll wait to see what's wrong first.
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Old 27th February 2009, 01:21 PM   #10
lickwid is offline lickwid  United States
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Here are a bunch of photos of the inside, and I took a closeup of the area where it looks like something fried. Also, I didn't take any of the underside of the board.

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