Seeking input on repair of Alpine MRV-F400 amp - diyAudio
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Old 22nd April 2009, 07:54 PM   #1
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Default Seeking input on repair of Alpine MRV-F400 amp

Hi all,
Here's the situation. Alpine MRV-F400 amp, appears to be no power. I came across Perry's site, which gave some valuable info on how I might be able to proceed.

I'm thinking either the output transistors or one or more Fet. The components on the board however do not show any obvious sign of damage/overheating in any way.

I plan to test the Fets tonight, to check voltage on them. If these all check out AOK, I will check the output transistors. The symptoms of the amp, it's very hard to say what it might be that's causing this. I've tested some voltage. There's full 12V in, I've found some varying voltage in different areas of the board. Even a very low voltage to the power LED light (light is not lit however).

There's no voltage on the speaker hookups whatsoever though.

I'll pop in here again tonight after I find results of the Fets. Just wondering if anyone has further input that I might be missing, or suggestions. I'm new to troubleshooting an amp, but have the tools necessary to swap components out of a circuit board.

Thanks in advance,


Tim
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Old 23rd April 2009, 12:09 AM   #2
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Ok, I've screwed one up now for sure. I fried one Fet, when it may not have been. I'm now thinking of just giving up on this amp and try to find/buy another that fits in budget.

Not too sure what to do. I can't find where to purchase these: IRFZ44N (except maybe pacparts.com, but at $5.00 each?!?)

There goes shot at testing. I fried it, as I had ignition on in my car and shorted the one Fet. Easy to replace I guess, but I can't figure out if these are the source of the problem of the amp not working. All of them read a 6 on my Ohm meter, which doesn't make sense.

Tim
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Old 23rd April 2009, 02:47 AM   #3
jol50 is offline jol50  United States
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Those are cheap at mouser and other places, 1.30 (mouser 844-IRFZ44PBF), and common. The PS mosfets are run in parallel, that is why they read the same in the board. Typical to have two groups, but when one blows it can trash all of that group or all in the amp because they run together. Some may test good and may even work, but they may have a short lifespan after the trauma. It is likely the amp is protecting if they are blown, if you see say under 50 ohms between any legs on any one of them, then the amp will be dead acting if it has no protect light to tell you that. Test the outputs the same way, shorting is common. If you replace them there are a few other things to check, but then you need to try to run it on restricted power so it does not smoke if something is still amiss. Those amps certainly are worth fixing IMO, but I tend to like them too.

Test them with no power using ohms or diode check on a DMM, Perry's site tells you how under transistors. I check for shorts, if none then look deeper.
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Old 23rd April 2009, 04:37 AM   #4
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Found and ordered 10 IRFZ44N. Going to just replace them all just in case now anyways. The fried one, took out part of the circuit board where center leg is on the transistor, hopefully I can get it soldered ok.

Tim
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Old 23rd April 2009, 03:20 PM   #5
jol50 is offline jol50  United States
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Another way you can do it if you don't know if anything else is bad, is take them all out. Then check the resistors on the left leg they need to be same value. Usually you can see half of them are connected to one driver and other half another, if any of the old IRFZ44 test good or use just two new ones, and put one on each group. This will run the amp if you don't play loud music and it is not still broken elsewhere. If it is then you only blow up the two and not all of them new. You will be upset if you put them in and they all smoke.

Note that the old IRFZ that might test good could still be bad or weak. Also put a single 10A fuse on the 12v and have all the transistors clamped to the sink. Can also run power through the 10A on a $10 DMM to see what it is doing I did that until I got a different meter, it works great. Should draw some for a second to fill the caps then about <2A with nothing connected to it. If it draws 10A or pops the fuse you still have a problem.

This is Perry's site I referred to and is very helpful if you have not seen it: http://www.bcae1.com/
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Old 23rd April 2009, 03:41 PM   #6
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Thanks! Much appreciated!

I'm going to switch out all the Fets when the new ones arrive. From the Ohm readings I did, it appears most/all are not working right anyways. Following Perry's instructions on testing them, they were throwing out numbers when the meter should have read zero.

Well, the amp owes me nothing, but simply wouldn't mind having it working, as it is my only amp at moment. I don't think I can get another decent (old school especially) amp for $60.00?

The Alpine cost me $20.

Tim
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Old 23rd April 2009, 06:31 PM   #7
jol50 is offline jol50  United States
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Epay has been strange lately a few things went high but these seemed to go cheap I thought: 290310559867 290310560203 The deals are there if you have time to shop, but still usually cost much more than parts for fixing an amp like that....depending on what is wrong with it. I've seen the above amps sell for more broken not long ago. I think the older style MRV you have are rated at 12v IIRC, so those ratings show lower.

If you run it on a couple mosfets, make sure you don't leave solder touching on the empty pads. It can get rid of your 10A fuse quickly. If it works fine load the rest in and test it the same way before you run it hard.

Where is everyone here....you guys leaving me all alone here on this post? Lot of things seem slow right now for some reason, not sure what everyone is up to, or they have been outside like me.
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Old 23rd April 2009, 06:48 PM   #8
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LoL,
Well, I was seeing alot of activity here yesterday, today seems quiet.

So, I pulled the one fried one, the amp should still power up with the remaining ones there (one missing)? If so, I could see if I can get further on testing. I was going to start removing the rest of them tonight, figuring I'd replace them all anyways. ($1.00 each, not a big deal, plus I'd have a couple spares)

Tim
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