SERIOUS BASS PROBLEM W/ Resident Evil: Apocolypse and M&K MX-100 (1 Viewer)

[Seth=L]

I was just watching Resident Evil: Apocolypse at my usual volume, which is sort of high. The opening segment were they do a shift from above ground suburbs to one of the entrances to the hive, there is some heavy bass, the frequency is so low I can count how many times a second the woofer moves back and forth. The excersion is very high, for the sub and the front speakers. At the volume when it happened the Carver amp went into protect mode and the sub did something awfull. About 4 seconds after the tones started the voice coil locked up to the back of the magnet structure, I know because the surrounds were flexing in plain view and I heard a pop noise when it slapped up against the magnet structure. At this point the M&K had already disconnected power and I beleive the capacitors were releasing the remainder of their stored energy. Now the bad part. The Carver amp turned back on, the M&K did not. I tried unpluging it and plugging it back in, even though a sub this old wouldn't have a reset feature I figured I would try any way. I also checked the in line fuse, which appears to be fine, but I am not sure. I then took the amp plate off and looked at the internal fuses, there are two, and they also seem fine. The internal connections to the power supply were very warm and the power supply was steaming hot, it burnt my finger a little when I touched it. The transistor was cool to the touch. Note that the M&K doesn't have an auto shut off and I leave it on all the time, because if I unplug it, the only way to turn it off, it dumps all remainder energy the caps are holding instantaneously after about 30 seconds of being unplugged making another terrible sound.

Does anyone know what went wrong here? Is it possible for the fuses to be damaged without actually appearing disconnected, like slight discolorations?

Someone please help.

 

[Rory Buszka]

Wouldn't it be best to contact the manufacturer (M&K) in this situation? They could tell you whether you've blown your driver or whether the amplifier is toasted, and they could also arrange for service to repair the damaged components.

This is what happens when you push gear to its limits -- things break. This may be the signal that you need a larger subwoofer if you want to enjoy movies at that level.

There are a few things we can test:

1. Is the woofer blown? Using a multimeter, check for continuity across the positive and negative terminals. If there is no continuity, then the voice coil has been toasted. If If the cone can be pushed in and out, but it makes a grating or scraping sound, that means that a different sort of thermal failure has occurred which has caused the voice coil to partially unwind from the former, or that the voice coil former has been deformed by bottoming out.

2. Is there a green power LED? Or, if it is a bi-color status LED, does it always stay red instead of turning green? This would indicate an amplifier fault. If the LED is dark, then there is some other type of problem that prevents the amplifier from getting power. Check for continuity across the fuses. If there is no continuity, then the fuses must be replaced. A visual check is not always useful for detecting a blown fuse unless it was a particularly catastrophic overload.

 

[Arthur S]

Change the fuses anyway. If that does not cure it, you have more serious problems, as Rory mentioned.

Sorry Seth, I've had my share of gear problems over the years and it is not pleasant. I'm going to stop talking about displays. You're priorities are clear, and I know you won't rest till you get this problem with your MX-100 taken care of.

Regards

 

[Seth=L]

It didn't bother me that much about the display thing, just wanted you to understand I am speaker crazy, allways have been. I guess you do understand now so that bridge is crossed.

I have also had a fair share of gear problems, some of which are at my own fault, and some not. I appreciate your input guys. I am going to Radio Shack for some 4 amp slow-blows. I hope that fixes the problem and it doesn't go up in smoke. I have had that happen before were the fuses blow, then the new ones blow along with the real problem like a bad transitor or resistor (those suck, they catch on fire, and it smells)

So once again, thank for the quick responces. And by the way Authur, I decided to keep my Infinity's and leave the NHT's for someone else to find, I am sure someone who needs them more than me will get them, I hope that is what happens anyway. If I bought them I would fear hexing another piece of equipment.

 

[Seth=L]

I checked the fuses for continuity, the in-line fuse was fine, but the 2 internal fuses tested bad. Considering they appear to be fine and well, whatever happened doesn't seem to be to bad. But just as well I thought I would ask for your opinions. Should I replace them with the fuses I just bought (they are the same rating and type, before you ask) or should I wait and test some other things. I don't want to risk more hurt to the amp or it's components. Would doing a continuity test on the power supply be a good idea. I am kind of dumb on this, but do they store any energy? It is still very warm, hot actually so I am very warry of it.

Thanks for any and all opinion and info.

 

[Seth=L]

I going to test the power supply now.

 

[Seth=L]

Just tested continuity on the power supply, it has continuity though I am not sure that means anything. Could it test OK on continuity and still be bad?

 

[Seth=L]

All right now I have really had enough of this thing. I replaced all the fuses and it blew them all. Nothing smells burnt and I don't see any damage. When I plugged it in after replacing the fuses it hummed while the fuses started to glow. Did I make a mistake in assuming that it needed all slow blow fuses, it doesn't say on the board what fuses to use, but the fuses that I replaced were 4 amp and they looked like slow-blows to me. I guess I really don't know what I am doing here, guess it is time to call M&K and ask them.

 

[ChrisWiggles]

If you're just blowing fuses, it sounds like the driver has shorted out, essentially the VC is damaged and shorted. If you bottomed out the driver, this is a fairly likely series of events. I would contact M&K for service/replacement driver.

 

[Seth=L]

So even if the thing doesn't grind or isn't locked up it can still be bad. When I push on the cone it seems OK, How can I test the drivers without risking damage to another piece of equipment?

 

[ChrisWiggles]

Yes it can be bad even if it doesn't rub. Rubbing indicates physical deformation of the VC or VC former. The VC can still melt and short out without doing this, which would cause the driver basically not to work or because it's shorted out, to cause the amplifier to go into protect mode or blow fuses as you indicate. I'm somewhat surprised that there's no rubbing from deformation, since that usually happens when you bottom out, and it's the rubbing that usually ruins/melts the voicecoil.

You should test the driver with a small battery(momentarily) to see if it moves back and forth with the battery. If not, it's probably shorted.

 

[brendy]

Reading your post it sounds like you have all the speakers set as large.When you do get everything fixed set all speakers to small and calibrate your system with a sound level meter and test tones.You just learned what happens when equipment is pushed beyond its limits.

 

[Seth=L]

I appreciate the input Brendy, but that isn't even possible in my setup. I am talking about a 2 channel setup with a seperate stereo components, the Rotel pre/pro is a pro logic processor that was designed for music in mind and surround sound as an extra feature, so no bass management what so ever. Also the problem is my sub. It was playing an extremely low frequency, inaudible, and was damaged in the process.

I have tested the woofers with the battery trick and a multimeter, they passed both tests. Now still considering there are no cinged or circuits that smell like burnt silicon that would leave me with the Power supply.

After removing all the stuffing (insulation enough to cover my entire floor, dear God) I noticed the shielding that keeps the copper windings covered had broken or perhaps even melted then broke, exposing the copper windings to the insulation. Though contact is not direct because of the wax coating on the copper wire. Recall how I said the Power supply was extremely hot, now this is likely due to being on all of the time, but with such demands placed upon it and heat creates resistance, so yea could it be the power supply, how do I test that.