How do I open a Bose Acoustimass 25 Series II - diyAudio
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Old 31st July 2007, 05:10 PM   #1
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Default How do I open a Bose Acoustimass 25 Series II

The amp has failed but I cannot work out how to open the cabinet.
Is there a special tool. What is the technique? Any help gratefully received.
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Old 31st July 2007, 05:41 PM   #2
kevinkr is offline kevinkr  United States
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Honestly speaking you should probably not work on this unit yourself: "There are no user serviceable parts inside"

Even if you are an accomplished EE Bose will not provide the required schematics to troubleshoot and repair this unit.

Still undaunted then IIRC this is the same case as the original LS-25 series and there is a catch at the end of the cover furthest from the input connectors that needs to be rotated, which you can do with a flat bladed screw driver, and you also need to remove a few screws from the bay where all of the connectors reside. Then tap the case with your fist at the far end and it should then slide off.

Note there is not going to be much you can do to fix this beyond replacing the fuse. (Note that the fuse is soldered in.) The bass amplifier is op-amp based with discrete class G output stage and the twiddler amps are monolithics with discrete class G circuitry shared between several channels.

The power transformer has a thermal fuse in it as well which is not replaceable. If you play the unit loudly for long periods of time and it is not adequately ventilated it is possible for the thermal fuse to open - if this is the case you will definitely need to send it in for service.

When plugged in there are hazardous voltages present on the top PC board where the power connector is located, whether or not the unit is turned on.

Power switching is via a triac controlled by whichever front end you have CD-5? 12V should be present on the mini plug (tip I think, but might be ring) when the music center is on..

There is also offset detection circuitry that will latch the unit off should any output have more than a volt or so of offset.

IMO This really is a job for Bose customer service. Sorry I can't be of more assistance, it has been a really long time since I left the company.
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Old 31st July 2007, 06:09 PM   #3
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I am not daunted by the thought of high voltages. I have been servicing since 1972 but just couldn't see the catches!
another engineer has ****ed the pots and I've been supplied manufacturer parts to fit.
many thanks for your assistance. I can see the catches now and can proceed confidently.
Regards
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Old 31st July 2007, 07:58 PM   #4
kevinkr is offline kevinkr  United States
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I should have mentioned that you need to pull the knobs off before removing the cover, but from what you have said you probably already know that..

Destroy the bass pot and the woofer amplifier stops working, however if there is no sound at all then another issue is at play.
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Old 31st July 2007, 10:23 PM   #5
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I was going to suggest a hammer........
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Old 31st July 2007, 10:51 PM   #6
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I like to think I am too professional and subtle to resort to the hammer approach. The cabinet designers are just too clever for me sometimes. The electronics I can handle with no problem.
Anyway, thanks again for all the info
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Old 31st July 2007, 11:00 PM   #7
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I have the non amplified bose acoustimass set, and it appears that the hammer is the only way to remove the drivers, and the box is thin crappy particle board so a hammer is appropriate to disassemble my model, I was more joking with you about trying to fix a bose product.

Good luck
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Old 2nd August 2007, 12:54 AM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by nunayafb
I have the non amplified bose acoustimass set, and it appears that the hammer is the only way to remove the drivers, and the box is thin crappy particle board so a hammer is appropriate to disassemble my model, I was more joking with you about trying to fix a bose product.

Good luck
Yeah, they are a bit hard to reach, but seriously a screw driver will do the trick.. hehe The mdf (it's not particle board) is not the biggest issue with this design - because of the small port diameter, port velocities can get high enough to cause some port noise, particularly audible if the satellites are disconnected. Still it is quite compact and that was the point of it all..

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Old 2nd August 2007, 01:00 AM   #9
kevinkr is offline kevinkr  United States
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Let us know how the repairs turn out..
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Old 2nd August 2007, 08:34 AM   #10
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well at least it is open now!
A previous repair attempt by persons unknown has left a trail of destruction. I could really do with a schematic now as the thyristor appears to be the wrong number/type. The mains transformer has been changed (although the original which was in a box with the bits) is perfectly OK. I like a challenge but without the circuit it is going to take a while to figure out what is going on. The end user is adamant that he wants it repaired.
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