Please Help, sub blown (1 Viewer)

[Seth=L]

I have an M&K MX-100 that is in non-working order. I have a thread about the starting problem, but know I have a new problem.

It was proposed the woofer or woofers were damaged during an intense passage in Resident Evil: Apocalypse, causing them to be shorted. When I replaced the amplifier fuses the amp protect fuses blew, but as far as I can tell no cinged circuits, no smells, and no smoke. What confounds me is when I plugged it in after replacing the fuses the woofer made a noise that I can only describe as a loud hum untill I unplugged it because I saw that the fuses were glowing. Under normal circumstances the sub makes a thump noise, and of coarse the fuses don't blow. Also when I unplug, when the sub still worked, it takes a few moments before releasing, instantaneously, the stored energy in the caps and makes the sound of a large nail being pulled out of dry wood, like a moaning creek, very unpleasant sound.

So are they the problem, I am not sure. How do I test the woofers to see if they are indeed shorted?

 

[John Meeks]

If it makes noise, the speaker is probably OK.

Did you disconnect all inputs/outputs? If so, did it still hum? I'd make sure everything's fully disconnected.

Is it a 60Hz hum?

It sounds like it's probly something wrong with the amp, not the speaker.

 

[Seth=L]

Sorry let me explain a different way, the amp does not work, because when I turn it on the fuses blow instantly. During that time the woofers make a distorted hum untill I am forced to unplug the sub. Something is preventing the amp from working, and none of the circuits are burning which they usually do when they are bad. I don't want to connect the woofers to another amp to test them for fear it will break them as well. Is there a way for me to test the woofers using a multimeter or something that doesn't involve more electronics dying.

 

[Seth=L]

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 of the Power Supply 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.

 

[John Meeks]

M&K doesn't have anything about the MX-100 on their site, so I'm guessing it's a powered subwoofer. Are you talking about the amp in the sub or a separate amp?

Let me see if I understand:

You have an amp, hooked up to a subwoofer, and a regular pair of speakers, including woofers. The amp and regular speakers work normally if not connected to the subwoofer. If you connect it to the powered subwoofer, some of the fuses blow, and some other ones glow red-hot, while the regular speakers are emitting a loud 60-Hz hum. Some of the things you said don't fit, so I'm confused.

Is your system doing something extremely bizarre, or am I missing something?

If you want to check if the speaker itself is OK, check the resistance with a meter (set to the regular ohms scale), it should be between about 2 and 10 ohms (or it should be close to the rated resistance, if it's printed somewhere, and it would have to be a huge speaker to be close to 2.). This will be hard to do if it's built-in to a sub, but assuming you can get to the terminals (make sure the damn thing is unplugged first!), you don't need to disconnect any wires, just test between the terminals. Most modern meters use a low-voltage resistance test to exclude any semiconductors.

As I said, I need to know more about your system.

 

[John Meeks]

I see you posted another message...

First of all, be careful messing with power supplies. Even if you have it unplugged, those capacitors can kill you.

And, I need to know more about your system before I even start to guess what's going on.

 

[Seth=L]

The MX-100 is in the archieves at mksound.com. The sub is internally powered so when I refer to the amp I am talking about the internal amp. My entire discusion is based on the sub and only the sub and it's amp.

 

[Seth=L]

The capacitors and the Power supply are seperate from one another, and I don't beleive the caps could kill me unless I was 105 years old and was already going to have a heart attack.

The MX-100 is a powered push-pull sub, similar to the MX-350 MK II in most aspects expect the MX-350 MK II has a little more power.

I have diagnosed the Woofers, they seem fine. I replaced the in-line fuse and two internal fuses, and the internal fuses blew when I powered the unit up. If the Power supply is bad, I would think that it could cause the distorted hum I heard whilst I watched the fuses heat up and turn orange. So now I think the Power supply is bad, from a logical point of view, because it was extremely hot for several hours after I initially unplugged it, and the shielding was damaged as well. By shielding I mean the plastic that keeps the copper windings shrouded so they don't touch anything.

I hope there is enough info, let me know if anything else is need to solve this catastrophe.

 

[John Meeks]

And, the sub does all this even if it's not connected to anything else (besides being plugged in)?

Since the speaker still seems to be working fine, I'd gues something is seriously wrong with the amp. It could be many things: bad capacitor, shorted transformer windings, something with one of the transistors... I don't know enough about amps to diagnose that myself, let alone try to do it over the internet.

I'd call M&K and tell them the amp is acting up.

If you want to, I don't see anything wrong with connecting the speaker to another amp to test it, just start with the volume all the way down, and turn it up slowly.

You must have jinxed me, my SVS just blew its fuse.

 

[Seth=L]

I get jinxed all the time, I bought an HSU for my bedroom, then my M&K dies. I considered getting some NHT 1.5's for the price of a back rub, but decided not to for a couple of reasons, but also for fear I would jinx another piece of equipment.

As for your SVS I hope that it is nothing serious, best of luck.

 

[John Meeks]

If you do want to mess with a potentially-charged cap, keep one hand behind your back. If you complete a circuit from one hand to the other, your heart can go into fibrillation, and if someone's not there with a defib, that's the end of it...

It's not necessarily the power supply... If the amp itself is drawing lots of power, it could cause the the problems you've talked about. Especially if the internal ones blow, they're probly between the PS and the amp.

 

[John Meeks]

I put a new fuse in and it's working fine (I have a bunch of fuses so I had a spare). It happened when I plugged it in, so it probly just hit the wrong part of the A/C cycle when it tried to charge its caps. Nasty blow too, the inside of the fuse is all blackened and silvered.

 

[Seth=L]

Ooh pretty! I made a bunch of those today in arts and craps.

 

[Seth=L]

Crazy thing is the sub has a series of 4 caps, all 10,000 microfarads, also the amp has one giant transistor, similar to the ones they used in pro-logic receivers before discrete amplifiers become more common. Though the one in the M&K is considerably larger.

 

[Arthur S]

My guess, you blew the power transistor(s).

 

[Seth=L]

Think I have it narrowed down to the power supply. Just hope there isn't any other problems. I will be calling M&K monday to inquire.

Everyone, thank you for your help.