Alesis m1 active mk2 power supply issue

[robb2231]

Hi first post on this forum but have been lurking for some time. Im having trouble repairing an alesiis m1active mk2 monitor. The fault is in the power supply, a couple of weeks ago one of the monitors cut out and after switching it off and on again at the switch it went on fine again for a while... until it cut out again.

After a bit of research i found that this was a common fault with the power supply in this model, the cause being a resistor which overheated toasting one of the capacitors. I Went ahead and replaced c35 and c8 as directed to on this forum http://www.neufeld.newton.ks.us/electronics/?p=232

After replacing these caps the fault has changed in that the speaker still cuts out after about 20-30mins usage but then switches itself back on again.

Would be very greatfull for someones help on this one.
Regards, Rob

[selldoor]

Re: Alesis m1 active mk2 power supply issue

Hi - Welcome to the forum- you may have been better in the Audio Section but perhaps the audio experts will recognise the heading.
First question is what caps did you use Manufacturer and Series. If you got them at maplins they may not be suitable for this application.

If you think about it - those two caps were dried out - the others in there are the same age and have been virtually in the same environment and if this was a computer monitor we would usually advocate changing most of the caps.

We can help a lot more if you please post good clear pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say a bit about yourself - skills tools etc.

[robb2231]

Re: Alesis m1 active mk2 power supply issue

Forgive me for being hasty, Here are pics of the board. My skills in electronics are very limited, as far as tools go I have a fairly decent soldering iron and multimeter but no esr meter yet. The cap that I replaced c8 with was a Jamicon 116C2(m) 50v 220uf and the cap that I replaced C35 with was an ANC RG 1uf 100v cap, both rated at 105°, both came from maplin
Have since found a similar thread on this forum here

https://www.badcaps.net/forum/showth...ight=alesis+m1

I will recap the power board fully as you suggested and as was suggested by Firespace in the thread he started. The caps are all the same ratings as those on his thread except that the ones used in my power board are in fact all Jun Fu. Will place the order today and update on how I get on, one question though do you think I am likely to get away with leaving the more expensive large 390uf 200v caps or should i replace these at the same time also? Im going to be ordering low esr panasonic caps from farnell, if i order any other brand ill be sure that they are Low esr and from the recommended list of good caps .
Thanks for your help

[ben7]

Re: Alesis m1 active mk2 power supply issue

After replacing these caps the fault has changed in that the speaker still cuts out after about 20-30mins usage but then switches itself back on again.

Seems almost like the amp chip is overheating, and it might be caused by excess voltage ripple on the power rail for the amp chip. (That means a bad capacitor is somewhere)

[budm]

Re: Alesis m1 active mk2 power supply issue

How is the power amp IC mounting? Is it making good contact with the heat sink, good heat sink compound?

[robb2231]

Re: Alesis m1 active mk2 power supply issue

The IC power amp chips mounting appears ok I will clean and re-apply thermal paste to double check this though have ordered new caps for both now leaving the large 200v ones out

[robb2231]

Re: Alesis m1 active mk2 power supply issue

Went ahead and ordered the 200v 390uf caps from Farnell too because of there minimum £20 spend, so hopefully once fixed these monitors should last

[robb2231]

Re: Alesis m1 active mk2 power supply issue

Sorry for this chain of posts but I have another question, the capacitors and several other large components were held in place with a white silicone type glue. Was this for heat insulation and/or protection against vibrations? What should I use to replace this? thanks again

[tom66]

Re: Alesis m1 active mk2 power supply issue

Sorry for this chain of posts but I have another question, the capacitors and several other large components were held in place with a white silicone type glue. Was this for heat insulation and/or protection against vibrations? What should I use to replace this? thanks again

There's no need to replace the glue. To assemble these boards, the components are placed on the board, glued down, and the board is wave soldered (run through a bath of molten solder.) If you hand solder the components you don't need the glue because you can hold them down with your free hand or bend the leads over.

[PeteS in CA]

Re: Alesis m1 active mk2 power supply issue

The RTV is there for shock and vibration protection. If this unit will be in an installation that isn't moved about, no need to replace the RTV. OTOH, if it's for a band that tours or something like that, definitely re-secure the caps.

[robb2231]

Re: Alesis m1 active mk2 power supply issue

Thanks very much guys! the speakers are for studio use only so will not be moved around so no need to replace the RTV then I guess the vibration caused by the speakers themselves would not be enough to damage the solder joints.
Have got the replacement caps now so will hopefully mount them tomorrow, have been working some late shifts lately so haven't yet had the time. Will test thoroughly and post on how it goes.

[PeteS in CA]

Re: Alesis m1 active mk2 power supply issue

... no need to replace the RTV then I guess the vibration caused by the speakers themselves would not be enough to damage the solder joints.

Actually, my son is a drummer, and we found that electronics didn't do well with the vibrations from that over time (months, not decades).

[robb2231]

Re: Alesis m1 active mk2 power supply issue

Ok replaced ALL of the electrolytic caps last night (both power supply board and crossover amplifier board) and cleaned and reapplied thermal paste.

Through testing it today all seemed well for about an hour untill the original fault occured and the unit cut out and switched itself off but did not switch itself back on again.
Strangely enough after switching the unit off at its switch the blue light lit up and speaker surged back into life for a second.

Any ideas as to what the fault could be?

[lambertian]

Re: Alesis m1 active mk2 power supply issue

My alesis m1 active mk2 psu board just failed too. Good luck!

[robb2231]

Re: Alesis m1 active mk2 power supply issue

please has anyone any ideas?

[selldoor]

Re: Alesis m1 active mk2 power supply issue

Perhaps you can repost pictures of both boards after the repairs. You should also check all the caps are the right way around/polarity and check all your board with a microscope for cold joints or cracks.
On the picture of the back of the board there is a bit of solder splatter around
the left hand resolders point - perhaps clean it up. Did you do that soldering- what was being soldered? and if you did not do it perhaps re-flow it.

[Togu]

Re: Alesis m1 active mk2 power supply issue

please has anyone any ideas?

Hi
Were you able to fix the power supply? I have the same situation :/

[highpulse]

Re: Alesis m1 active mk2 power supply issue

my both boards are dead , easy way to fix this , as im not going to spent 250 dollars in 2 boards , since mine damaged in multiple areas , grabed a marrantz amp , and inserted power of the output of the marrantz amplifier to the cross over , my speakers are working for a good time now fuck the blue light , its working and can keep making music !

[nfasousa]

Re: Alesis m1 active mk2 power supply issue

Hi

I have 2 M1 active 620. The first burn about 2 years ago and I can repair. Replacing D1,D2;D3,D4. RT1, Q1, Q2, C8, R3, AND R4.

But yesterday Burn other.

I replace D1,D2;D3,D4. RT1, Q1, Q2, C8, R3, R4, R5, D5. But is dead. I dont know what I can do more. Should I replace UC 3844N?

I attatch shematic, the green points are components I replace.