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M&K MX150THX powered sub power on, but not working

 

New member
Username: Scott0521

Post Number: 1
Registered: Jan-18
Recently purchased a new receiver (Denon AVR x4300h) and tried using Audyssey to calibrate my speakers to my room. My sub (M&K MX150-THX) was working when I started the process but I screwed something up because it went out during the calibration process. The red LED is on so I know it has power going to the unit. There are two 6amp fuses on the amp board and I tested them and they're both good. There are no "popped" capacitors and no burning on the circuit board. Everything looks fine. M&K no longer supports this model as it's pre break up of their partnership. I've asked for support and I've been told it could be a bad amp or a blown speaker (this unit has two; one front and one bottom firing). I can't afford to just keep trying to replace things hoping it fixes the problem. Does anyone have any ideas how I can debug to isolate the issue. I was able to borrow another powered sub and it works on the Denon, so I know it's a sub issue and not a receiver issue. I've plugged an RCA cable into the back of the sub and touched the other end and get no sound out of the sub. Other than those checks, testing the fuses, and visually inspecting the amp panel for blown capacitors or burn marks on the circuit board I'm out of things I know to look for. Any help would be appreciated. I hate to lose this sub, but don't want to keep throwing money at it to try and fix. Thanks, Scott
 

Gold Member
Username: Magfan

USA

Post Number: 3470
Registered: Oct-07
Anyway to get the boys at M or is it K? to part with a schematic.

That way, you can go to an electronics repair show and stand a reasonable chance of a 'fix'.
 

New member
Username: Scott0521

Post Number: 2
Registered: Jan-18
The original M&K (Miller and Kreisel) company folded in 2007. My sub goes back to 2002 so it's from the original partnership. Because the company ended I haven't been able to find a schematic or replacement parts on this model. I was able to get Ken Kreisel's e-mail address prior to the holidays, but I haven't e-mailed him yet. Kreisel is the "K" of "M&K". I'll reach out to him and ask if he's able to provide me with a schematic. If I luck out and get one, what would that do for me? When you said an electronics repair show, did you mean shop? I've looked for one in the area (Chicagoland) and haven't found one that sounds like they would be worth going to (based on Yelp reviews). Also, the sub is heavy and would be difficult to ship. That's why I was hoping to try and troubleshoot to the point of finding the bad component.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18482
Registered: May-04
.

The first question is, can you physically remove the drivers from the enclosure?

I have sold the M&K products and they're rather well built which can, particularly years after initial assembly, make them very difficult to get "unstuck" from their mounting.


If you can't remove the drivers from their mounting, there's not much you can physically do to solve a problem with the drivers. You gain nothing if you destroy a component trying to fix a component.


If you can remove the drivers, test them individually outside of the enclosure. Or, if you can SAFELY run jumpers to their input terminals, test them while they are inside the enclosure knowing you may only prove your sub is shot.

You probably can't obtain exact replacement drivers today but you can install "similar" drivers purchased from an after market retailer such as Parts Express. If the drivers are not labeled from their original manufacturer, finding out who built the drivers for M&K would be your next best step in obtaining the closest existing driver to your originals.

It would be a bit unusual for both drivers to blow out at the same time. Though, depending on what you actually did, not impossible. I would suspect the output transistors on the amp to have gone South. The problem remains replacing them. Assuming similar transistors or their equivalents are available, you can try replacing the parts but you won't know what may have occurred upstream from the outputs. If you can't check for damaged parts in front of the transistors or you can't adjust, say, bias Voltage coming into the transistors, you'll likely blow up the new components.

If you can't find a repair shop willing to take on the sub and you can't determine which part is defective, you are pretty much screwed.


There's no need to ship the enclosure. If you can localize the damaged parts, you can ship only those parts. The enclosure has nothing to do with the electrical operation of the amp or the speakers.


.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18483
Registered: May-04
.

If you determine the drivers are still operational, you can replace the OEM plate amp with another.
 

New member
Username: Scott0521

Post Number: 3
Registered: Jan-18
Thanks Jan. I'm going to work on getting to and testing the drivers this weekend. As you said, if they test ok, it'll narrow it down to the amp. If that is what's bad, I'd love to be able to troubleshoot it and fix the problem with it, but at least I know I can purchase a replacement and get my sub back again. I appreciate you taking the time to help. Scott
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