Hello, long time lurker first time poster. I hope I can pick your brains about this power supply issue I have. Apologies in advance, this is a wordy post 😱
My friend has a pair of Alesis M1 mk2 active speakers and a while back one of them starting working intermittently. After a while, it finally just stopped working all together.
I had a look online, looks like the speaker is riddled with common problems with capacitors and heat.
Here's a pic of the top assembly for the power supply:
The big caps c6-7 were looking pretty poor (doming on the top) so I swapped them out. While I was doing that I swapped the rectifier diodes D1-4 and capacitors c35 and c8 which had discoloured. (Most of this was recommended from a youtube video I watched where they had a similar problem).
I also swapped the suppression caps C1 and C2 as they were cheap and the video suggested it.
So far, success! It powered on again, it plays music but if the volume is increased rapidly or it is left to play for 20 minutes at a reasonable volume the power cuts out (LED goes off, speaker goes quiet).
I tested the woofer and the tweeter separately and discovered the woofer works fine, at any volume but when the tweeter is connected I get the same issue with it cutting out.
So I've narrowed it down to the tweeter but as the tweeter sounds fine when it is playing (no audible distortion, checked the resistance across it and got 4 ohms as expected) i'm thinking there is an issue with the 18v rail that supplies it.
Has anyone had any experience with this or could they point me at a few places to look? The J5 connector on the left of the board takes the power to the xover/driver board where both speakers connect.
I was going to check that the 18v (1A) is present at this J5 connector point but couldn't work out which pin was ground and thought I'd better not risk shorting something and making the problem worse.
I've attached the service manual for the speaker as well, if this isn't allowed I can remove it.
Final apology about any incorrect terminology or approaches I've used. I'm fairly new to power supplies, especially switching supplies!
Any advice, even just 'chuck it in the bin' would be appreciated!! 😀
My friend has a pair of Alesis M1 mk2 active speakers and a while back one of them starting working intermittently. After a while, it finally just stopped working all together.
I had a look online, looks like the speaker is riddled with common problems with capacitors and heat.
Here's a pic of the top assembly for the power supply:
An externally hosted image should be here but it was not working when we last tested it.
The big caps c6-7 were looking pretty poor (doming on the top) so I swapped them out. While I was doing that I swapped the rectifier diodes D1-4 and capacitors c35 and c8 which had discoloured. (Most of this was recommended from a youtube video I watched where they had a similar problem).
I also swapped the suppression caps C1 and C2 as they were cheap and the video suggested it.
So far, success! It powered on again, it plays music but if the volume is increased rapidly or it is left to play for 20 minutes at a reasonable volume the power cuts out (LED goes off, speaker goes quiet).
I tested the woofer and the tweeter separately and discovered the woofer works fine, at any volume but when the tweeter is connected I get the same issue with it cutting out.
So I've narrowed it down to the tweeter but as the tweeter sounds fine when it is playing (no audible distortion, checked the resistance across it and got 4 ohms as expected) i'm thinking there is an issue with the 18v rail that supplies it.
Has anyone had any experience with this or could they point me at a few places to look? The J5 connector on the left of the board takes the power to the xover/driver board where both speakers connect.
I was going to check that the 18v (1A) is present at this J5 connector point but couldn't work out which pin was ground and thought I'd better not risk shorting something and making the problem worse.
I've attached the service manual for the speaker as well, if this isn't allowed I can remove it.
Final apology about any incorrect terminology or approaches I've used. I'm fairly new to power supplies, especially switching supplies!
Any advice, even just 'chuck it in the bin' would be appreciated!! 😀
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1) Why is this post in the Class D section? The amps are class-AB LM3886 chips
2) There's a pretty extensive repair thread on these Alesis over on badcaps.net - Repairing Alesis M1 Active mk2 Monitor Speakers - Badcaps Forums
2) There's a pretty extensive repair thread on these Alesis over on badcaps.net - Repairing Alesis M1 Active mk2 Monitor Speakers - Badcaps Forums
Also forgot to mention that when both the tweeter and woofer are connected, if it cuts out I can gently tap the back plate a few times and it will cut back in for a few seconds. I thought this might have been a dry joint or loose connection but couldn't see any issues with the solder or cabling!
Yes I see, apologies I meant to put this in the Chip Amp board. Not a good start to the board 
Ok I did look through the thread but no one seems to have the same issue I am having. I'm trying to avoid blindly replacing anymore components before checking so I'll read through it and see if there is any advice on where to check the dc rails.
Thanks!
Ok I did look through the thread but no one seems to have the same issue I am having. I'm trying to avoid blindly replacing anymore components before checking so I'll read through it and see if there is any advice on where to check the dc rails.
Thanks!
thread moved to Chip Amps- Status
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