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.
Is there a special tool. What is the technique? Any help gratefully received.
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.
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.
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
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
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.
Destroy the bass pot and the woofer amplifier stops working, however if there is no sound at all then another issue is at play.
........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
Anyway, thanks again for all the info
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
Good luck
nunayafb said:
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..
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.
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.
Hi,
I strongly agree with nunyafb 😀
Hit it with a hammer......it´ll be fun and You won´t hit anything of value 😀
jauu
Calvin
I strongly agree with nunyafb 😀
Hit it with a hammer......it´ll be fun and You won´t hit anything of value 😀
jauu
Calvin
I would looooooove to see some pics.
Other than that it might be easier to just gut the thing and insert some small monolithic chip amps ?
Other than that it might be easier to just gut the thing and insert some small monolithic chip amps ?
I'm just wondering what the objection is to getting this thing fixed by Bose Customer Service? I assume that if the original purchaser could afford over 1000 British pounds to buy it, he would be interested in getting factory service, and should be able to afford it, something is really fishy here. Bose customer service is very good.
Without understanding how the thing works I doubt you have a lot of chance of success, and I'm not doubting your capabilities. I doubt at this point I could fix one without the schematics.
This unit includes the surround sound decoder, a microprocessor to manage the decoder, audio mode (stereo or surround) amplifier muting, etc. I will give you a hint, you will need the head unit to do any diagnostics - and I would temporarily short the triac out to power the unit up - until you can find the right replacement. (Verify that there are no blown devices in the power amplifier module first. Install correct 1.6A slow blow fuse, and also limit the current externally if possible. Unit will not function correctly much below 200V.) Reinstall the original transformer first if the thermal fuse is not blown. The opto isolator is probably bad too if the triac has failed. DO not use a zero crossing detector type opto as a replacement!!!
Without understanding how the thing works I doubt you have a lot of chance of success, and I'm not doubting your capabilities. I doubt at this point I could fix one without the schematics.
This unit includes the surround sound decoder, a microprocessor to manage the decoder, audio mode (stereo or surround) amplifier muting, etc. I will give you a hint, you will need the head unit to do any diagnostics - and I would temporarily short the triac out to power the unit up - until you can find the right replacement. (Verify that there are no blown devices in the power amplifier module first. Install correct 1.6A slow blow fuse, and also limit the current externally if possible. Unit will not function correctly much below 200V.) Reinstall the original transformer first if the thermal fuse is not blown. The opto isolator is probably bad too if the triac has failed. DO not use a zero crossing detector type opto as a replacement!!!
highviewvideo said:
Anything BOSE can (and should) be opened with a Sawzall:
An externally hosted image should be here but it was not working when we last tested it.
OK So triac is faulty. original transformer Ok. Guess what- the 110v links hadn't been changed for 240v! Unit works with triac bypassed. When I get the correct type repair will be complete.(Any ideas of the correct part?)
I was passed the repair from a local retailer who screwed it up and is probably too embarrassed to send it back to Bose. Anyway I don't normally run in to problems. It was basically getting the thing open! Sounds quite nice actually. Maybe not for the purists but not as bad as some guys out there make out.
I was passed the repair from a local retailer who screwed it up and is probably too embarrassed to send it back to Bose. Anyway I don't normally run in to problems. It was basically getting the thing open! Sounds quite nice actually. Maybe not for the purists but not as bad as some guys out there make out.
There should be a number of triacs that will work in this circuit. I don't have the specific part number to hand, but can probably dig it up at some point.
What you need is a standard sensitivity triac (not a sensitive triac) 600V-800V 6A, gate current a couple of mA. It's not too critical. Check to make sure the MOC is ok, if not it should be replaced with the same type. First cycle inrush current can be quite high so make sure the selected triac can handle a few cycles of >20A.
I assume the unit got plugged into 240V before you got it and changed the jumper, and was not too happy about that.. Check the electrolytics for signs of damage as they were overvoltaged at that moment. There are some 5.1 ohm 1/4W fusible resistors feeding the voltage regulators that you should also check. They should measure within 5% of their nominal value otherwise they should be replaced. Sometimes when overstressed momentarily their resistance increases significantly, and they may decide to open (much) later with some very perplexing results. IIRC these can be replaced without fully disassembling the power amplifier module.
To get to the amplifier module there are 8 screws (10? I forget) that have to be removed to remove the bracket the amplifier sits under. Do not remove the plastic plate from the bass module as sealing is crucial and the original gasket should not be reused. When reinstalling tighten the screws by hand only and do not over tighten as it is easy to strip out the flange area as it is only mdf.. If you changed the power transformer you have probably already figured this out.
Watch for twisting in the woofer cable where it comes out of the box , avoid pinching. (Shorts possible - will destroy bass amplifier)
You can pop apart the amplifier module with a large flat blade screw driver if you need to - stick it in the slot and pry gently, so that you are pushing against the plate - do not twist. When you reassemble make sure the heat sink spring clamp is aligned properly with the holes in the board before you put the cover back on. Put end of cover without the aforementioned notch into the notch in the heat sink and press until the notched side locks into the notch on the other side of the heat sink. Be very careful when handling the heatsink not to scratch the area where the devices sit as this is a non-conductive anodyze. You should apply new grease to the devices before reinstalling the board.
Purchased on eBay? The music center that came with it will need a replacement wall wart..
What you need is a standard sensitivity triac (not a sensitive triac) 600V-800V 6A, gate current a couple of mA. It's not too critical. Check to make sure the MOC is ok, if not it should be replaced with the same type. First cycle inrush current can be quite high so make sure the selected triac can handle a few cycles of >20A.
I assume the unit got plugged into 240V before you got it and changed the jumper, and was not too happy about that.. Check the electrolytics for signs of damage as they were overvoltaged at that moment. There are some 5.1 ohm 1/4W fusible resistors feeding the voltage regulators that you should also check. They should measure within 5% of their nominal value otherwise they should be replaced. Sometimes when overstressed momentarily their resistance increases significantly, and they may decide to open (much) later with some very perplexing results. IIRC these can be replaced without fully disassembling the power amplifier module.
To get to the amplifier module there are 8 screws (10? I forget) that have to be removed to remove the bracket the amplifier sits under. Do not remove the plastic plate from the bass module as sealing is crucial and the original gasket should not be reused. When reinstalling tighten the screws by hand only and do not over tighten as it is easy to strip out the flange area as it is only mdf.. If you changed the power transformer you have probably already figured this out.
Watch for twisting in the woofer cable where it comes out of the box , avoid pinching. (Shorts possible - will destroy bass amplifier)
You can pop apart the amplifier module with a large flat blade screw driver if you need to - stick it in the slot and pry gently, so that you are pushing against the plate - do not twist. When you reassemble make sure the heat sink spring clamp is aligned properly with the holes in the board before you put the cover back on. Put end of cover without the aforementioned notch into the notch in the heat sink and press until the notched side locks into the notch on the other side of the heat sink. Be very careful when handling the heatsink not to scratch the area where the devices sit as this is a non-conductive anodyze. You should apply new grease to the devices before reinstalling the board.
Purchased on eBay? The music center that came with it will need a replacement wall wart..
since I have many contacts in the trade I will put out the feelers today and see if anyone has these vintage tubes in their workshops. I will be glad to be of help.
I would definitely be interested, but they're likely to be a bit beyond reach due to their rarity - and even new they weren't cheap...
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