Mordaunt-Short Alumni 9 MS339 subwoofer repair

[petrolbloke]

Wondering if anyone has any tips on getting into this subwoofer so I can attempt to diagnose and fix it. The issue is that it doesn't power on. No power light and no sound. Have tried two known good kettle leads so it must be a fault inside the sub.

I removed all the torx screws around the edge and tried to pry the plate away around the screw holes but it didn't come away.

[OutInTheShed]

Have you checked the fuse in the carrier under the kettle lead?


Personally, I'd either try googling for a service manual, or undo the 4 Philips screws in the lower right quarter....

[mgv8]

I have not taken that model to bits but done a few now and you look like it should pop out now. Its heavy so may be glued or stuck?

[petrolbloke]

Ah-ha... didn't realise it had its own fuses. Removed the holder and the 250V one is blown. Will need to source a spare T1AL fuse - hopefully that's all that's wrong with it!

[OutInTheShed]

petrolbloke said:

Ah-ha... didn't realise it had its own fuses. Removed the holder and the 250V one is blown. Will need to source a spare T1AL fuse - hopefully that's all that's wrong with it!

Normally fuses don't just blow, but a new fuse is a cheap thing to try.
I get odd things like that from RS components or Rapid or Farnell, but there are probably people selling them on ebay.

If it's a 1A fuse and the amp draws up to 250W instantaneously, then it could just be the fuse.

I could be vaguely in the market for a project sub if you can't fix it.....

Good Luck!

[Deranged Rover]

Interesting - T1AL is correct according to the rear panel but that seems a bit low to me, given the quoted maximum power consumption of 240W.

[OutInTheShed]

Deranged Rover said:

Interesting - T1AL is correct according to the rear panel but that seems a bit low to me, given the quoted maximum power consumption of 240W.

The max audio power will be for a short bang on a bass drum.
It's quite common for audio stuff to have strangely high max power printed on the back panel.
Often way above what an amplifier can peak at.

A 'one amp fuse' should carry 1 amp forever.
Depending on the exact flavour of fuse, it might be required to carry 3A for a second or two and blow at 3A after several seconds.
Some fuses oxidise a bit over the years and become easier to blow.


Seems to me, not so many years ago, fuses rarely blew. People used to joke about the transistors blowing to save the fuses.
These days I seem to see more stuff where there's nothing wrong apart from the fuse?

[petrolbloke]

Result - new fuse has fixed it.

[OutInTheShed]

But, we need to know how to take it to bits!

[petrolbloke]

Ha!

We'll luckily I didn't need to take it apart but I did find this thread on AVForums with some more info:
https://www.avforums.com/threads/mordaunt-short-ms...

[Danny Bar]

petrolbloke said:

Ah-ha... didn't realise it had its own fuses. Removed the holder and the 250V one is blown. Will need to source a spare T1AL fuse - hopefully that's all that's wrong with it!

Hi, sorry to be a pain, but my Alumni 9 has just stopped working in the same way yours did. No power! However I know nothing about this stuff. I read a replacement fuse fixed your problem. I don't know if you meant you replaced the fuse in the power lead or if there is a fuse in the unit itself. Are you able to let me know what I may need to check and the type of fuse I may need. It'll be greatly appreciated. Kind regards, Danny

[Captain_Morgan]

Danny Bar said:

Hi, sorry to be a pain, but my Alumni 9 has just stopped working in the same way yours did. No power! However I know nothing about this stuff. I read a replacement fuse fixed your problem. I don't know if you meant you replaced the fuse in the power lead or if there is a fuse in the unit itself. Are you able to let me know what I may need to check and the type of fuse I may need. It'll be greatly appreciated. Kind regards, Danny

Have you tried reading the thread linked in the post above yours?

[StescoG66]

Danny Bar said:

Hi, sorry to be a pain, but my Alumni 9 has just stopped working in the same way yours did. No power! However I know nothing about this stuff. I read a replacement fuse fixed your problem. I don't know if you meant you replaced the fuse in the power lead or if there is a fuse in the unit itself. Are you able to let me know what I may need to check and the type of fuse I may need. It'll be greatly appreciated. Kind regards, Danny

If you look at the moulding the mains lead goes into, you’ll see a little panel. The glass fuse is in there - it just prises open and fuse should out. Don’t for pity’s sake put a standard plug fuse in there. Replace like for like.
Power surges and also switching off the plug while it’s powered up can cause it in my experience (Tannoy TS1001 sub here..,)