Alpine MRD-M501 = Fail ?

[DrReamery]

So after finally amassing the parts to put together MR2 system 2.0, I'm at the tuning part. I've run into a snag though:

I picked up a used (great shape on inspection) Alpine MRD-M501 on ebay, and during tuning I noticed the temperature steadily rise. The digital readout said it was about 67 degrees when I began, and a couple hours later it was just shy of 130 degrees! Too hot to keep your hand on. In the time of those couple hours I ran the system at moderate volume for ten minutes maybe three times, and the other amp (MRV-F540) was barely warm to the touch. I seriously doubt the sub-amp should reach those temps.

The other thing I noticed was the subs were "flexing" when I had a track paused. PAUSED! No sound was coming out of the subs (or the rest of the system) but they were moving back and fourth at what looked like most of their excursion with a slight stutter. Is this bad for my speakers?

The JL 8w3v2 D4 subs I THINK were fine at first, but now there's a definite rattle / vibration / baffle / waffley sound to one of the subs but not the other. I took that sub out of the box and made sure it was wired right (it's a dual-voice-coil). Then I inspected it. Nothing was wrong with the spider, cone, or wiring; it looks brand new. I put it back in the box making sure it was sealed and then I double checked my series wiring (which is brand new) through the car. I did the 9v battery check and the speaker moved forward, just like it's supposed to. Finally, I swapped the wiring for the boxes and the vibration stayed with the same sub.

I used the DMM tutorial on JL's website to set the gains, and on the sub amp it's set to 0 input (-24 - 0 range) and the gain is at +6 (0, +6, and +9 are the possibilities). I'm running at 4 Ohms. The amp puts out a rated 275 watts feeding the subs that want 125 each.

Bottom line: Does it sound like I have a busted A55 amp? Is it possible it damaged my sub? What the hell is up with a moving, flexing sub when the music is paused?!? Is 130 degrees normal?

Thank you so much for taking the time to read this, even if you can't help.

Derek-

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[BoxdGM 10+ year member]

the only thing I can think of is check the load at the wires that connect the subs to the amp. maybe too low resistance? and 130 is getting into the damaging range (for computers at least) so I'd try to figure it out before you run the amp anymore to avoid cooking it. but you'd think it would go into thermal protect if it wasn't capable of runnin that hot so I'm not sure

 

[Canaan 10+ year member]

Check your ground.

Make sure the amp is getting over 12v when playing.

 

[DrReamery]

BoxdGM: I did like you said and checked the load at the amp. It's wired with two "D4" subs in series so it's supposed to be 4 Ohms. The DMM said 3.5, so right about where it should be. I also checked the resistance at each of the boxes and they were both 6.something Ohms.

canaan: I'll give that a shot. I just put the DMM leads on there while it's running right?

UPDATE: I hooked my other Alpine sub-amp MRP-M350 (200x1@4Ohms) to see what it would do. The subs still sounded baffley with that audible, cheap sounding vibration (that's right, both of them have it now), but they didn't sit there flexing when the HU was paused. Clearly there's SOMETHING wrong with the MRD-M501.

I hooked the MRD back up to see if it would still do it, and sure enough, with the HU paused the subs flexed. ALSO!!! With the volume on the 9835 turned down to 6, where the music is almost inaudible, the subs flexed (music playing). I turned the subs off through the HU and they still flexed with the volume up or down.

The best I can figure is that any time the amp is on but there's no voltage coming from the HU, the subs flex. Since I had a track paused for over an hour, the subs probably sat there flexing and I'm assuming they got damaged from this flexing. Finally, for whatever reason this causes the amp to heat up quite a bit. So I think I have a busted amp whose symptoms caused damage to my subs.

Can anyone explain what the flexing might be and if it is actually damaging? Has anyone heard of this kind of problem with an amp?

Thanks for the two replies so far.

D-