Question about Bose Lifestyle 28 System
Have replaced fuse with correct type but the fuse blows the moment the power switch is turned on. when cable between power switch / fuse and the circuit boards is disconnected and the power is switched on fuse is ok. could this mean a short or problem within the circuit boards
Posted by Anonymous on
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Posted on Jan 02, 2017
Honestly speaking you should probably not work on this unit yourself: "There are no user serviceable parts inside"
Even if you are an accomplished Electrical Engineer Bose will not provide the required schematics to troubleshoot and repair this unit.
Are you still undaunted . . . then if the case is the original LS-25 series, there is a hidden catch at the end of the cover furthest from the input connectors that needs to be rotated (until a plastic tab is sticking out), 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. Remove the two knobs from the side of the cover. Then hit the case with your fist at the far end (plastic tab) and the cover should then pop off. You may have to hit it hard, with an upward motion.
Note there is not going to be much you can do to fix this beyond replacing the fuse. (Note that the fuse may be 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.
For more information see following web site:
Posted on Mar 01, 2009
SOURCE: Bose PS321 No Sound
The power supply is 29 volts raw voltage,the IRFI44N fet on the power board is used is a switcher.
It reduces the voltage to 17 volts which is required for the AV3-2-1 meda center.The higher voltage biases the sound to cut off and can blow the drivers,try changing the fet and see if plays........
Posted on Apr 05, 2009
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