Alpine MRV-M500 Intermittent Problem

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Hi I'm new here and need some advice.

I have an Alpine MRV-M500 amp driving a JL Audio 10W3 sub. It's been fine for a long time but it started playing up a week ago.

Under moderate to heavy load the amp would cut out intermittently for a few seconds then come back on again. I'm not sure if it went into protection mode as it only has the one blue led, but it was powered the whole time.

I had it on the bench and noticed it draws 1.2A when switched on without any load on it, so I thought one of the output FETS might be faulty. I replaced all 4 plus the two driver IC's. Hooked it up again and it was working fine for around an hour until it cut out again. It now seems it's temperature related as it will start working again after half an hour or so.

Does anyone have any ideas what could be causing this? I'm thinking possibly thermal protection kicking in for no reason. The amp is barely getting warm up until it cuts out.

I can't find the circuit diagram for it anywhere which would make things a lot easier.
 
Thanks for the replies and for the service manual. If the LED turns red when it goes into thermal protection mode, then that isn't my problem as the LED stays blue.

The strange thing is the characteristics of the fault keep changing bizarrely. It now works the entire time until you start really pushing it. If pushed to the limit it will cut out only for a second or so then kick back in. It will keep doing this until you back down on the volume.

Not really sure how to diagnose this as I'll have to have it on the bench at full blast until the fault happens. I can see the workshop's reaction with me sitting there with ear defenders on making a hell of a noise. Lol.
 
I've finally got round to have a look at the amp and just realized I have the MRP-M500, not MRV-M500. No wonder I couldn't find anything on the board that was in the manual!

Does anyone have a link to the correct manual please? I scoured the net but can't find it.

Thanks.
 
The MRP-M1000 service manual will be similar. Just half the MOSFETs and lower power supply voltage.

The MRV-M500 switched to a half bridge design with half the number of output MOSFETs, but is otherwise quite similar.

I found it thanks. I opened the amp up and went through everything and couldn't find a thing wrong with it, but it still had no output. Really scratched my head and then thought let me double check the sub. Turns out one of the tinsel wires had snapped leaving the sub open circuit. :eek:

Strange thing is I couldn't get any output from the amp at all while the (open circuit)sub was connected. As soon as I disconnected it completely the output was there, so it looks like the amp went into protect mode for some strange reason.

I've sorted the sub and now everything is working the way it should.
 
Happiness short lived. Amp is still randomly going into protect mode. I think it's the sub causing it but I don't have another sub at the moment so I can rule it out.

On the plus side I'm thinking of replacing the amp and sub for something with a bit more power as it's driving me nuts!
 
do you find the real problem?

i have one with the same problem. i change outputs and irfs20956 ic. it goes out one second then works again, only at high levels and 2 ohm load and the amp with temp.

im looking for problems in the inductor, when the amps output cuts, i push down the inductor and the output works again.
 
One leg of the inductor wraps over the top of the inductor. What I have found on these amps is the inductor will vibrate and rub through the wrap that rests on top of the inductor. I lift this leg, place an insulator across the top of the inductor and then solder it back down. Also make sure you check the inductor bond to the board. I usually have to add some silicone. Should be fine after that. I recommend this for any amp with this inductor situation regardless of current condition. It's an ounce of prevention.
 
For posterity and future searches, this is what I do with these inductors. FWIW, These amp are not usually worth the trouble to repair them but if you're going to do it, you might as well go the extra step. I've personally watched several of these amps be just fine until you touch the inductor. Then the current draw goes through the roof. Nix it now. That is fish paper cut long enough to wrap around the inductor. It's folded for double thickness. This will mitigate the issue. Good luck.
 

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MatthewS
Is is a modification you perform on the MRP-M500, the MRV-M500 or perhaps both? The OP stated MRV-M500 in the thread title but later clarified he has a MRP-M500.

I finished repairing two MRV's a couple weeks ago but would consider performing this modification to increase reliability if this is a common failure.
 
MatthewS
Is is a modification you perform on the MRP-M500, the MRV-M500 or perhaps both? The OP stated MRV-M500 in the thread title but later clarified he has a MRP-M500.

I finished repairing two MRV's a couple weeks ago but would consider performing this modification to increase reliability if this is a common failure.

MRV's. I haven't had an MRP here in a long time and can't recall the inductor. If they used the same implimentation, i'd mod those the same way. Basically the side closest to the outputs in that photo is somewhat pinned in place by the 1st lead. The second lead comes over top to pin the other side down. But there's room to wiggle. And it usually does. If it wears through on that end, there will be problems. Good luck.
 
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