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KEF Q900 BAss driver.

Rega

doc_sreenu

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Hi,

after a long time, coming back. now with a problem.

My faithfully performing KEF Q900- since 2012, has gone kaput:sad:- its bass driver is non functioning.
had a similar issue with other speaker- 6 mths back- was replaced under warranty.

now the speakers are out of warranty.:sad:

i had asked a quote from PRO- FX people, they are quoting 10k for the bass driver.

am in a fix what to do next.:rolleyes:

kindly put forth some suggestoins.

regards,

srini
 
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Audio_Freek

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Oh really Sorry,

Did you try looking on to the issue? Has the Coil burnt or out heat ? or any connectivity issue? Any Jam in the Magnet ?etc

There could be issue with the Cross over too. Be sure before you place a order for replacement.
 

doc_sreenu

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Thank you audio freak, for your suggestions- am a noob in this- have dismantled the drive from cabinet- nothing looks fried?? or smoky/burnt.

what i have observed is excessive movement of the cone compared to others.

to check for circuits- i might need to open all the drivers- which am wary of.

The tweeter of UNI Q driver is functioning well. the cone of UNI Q and rest of drivers are not functioning.

confused what to do?

regards,

srini
 

Audio_Freek

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1.Unplug the speaker wire from the affected speaker
2.Remove the bass driver(which you found faulty) from the Speaker Box
3. Connect the speaker wire (coming from the Amp) to the bass driver
4. Just try play the song on a normal volume and identify whether the driver is showing some moment.

In case the Voice coil is burnt then the bass driver will not show any moment or music
In case the Bass driver is working then, it could be internal wiring or cross over problem.

All the best,(Note: the test is to know only whether the bass driver is working and not to test its potential so try with Mild volume only)
 

Fantastic

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You better understand your speaker before you "do things to it " !
A couple of drivers on it are passive radiators ( ABR's) which are more floppy than the other drivers and have no voice coil . I'm assuming you have the same speaker being talked about here. The real bass driver with a voice coil is the third from the top ( according a Youtube video!). The other two ,above and below the middle 8 inch bass driver ,must be ABR's ( no voice coil ). No point removing the ABR's unless you need to do that to access the crossover if it is located behind them.

" All the drivers, including the tweeter, have aluminum domes with the top Uni-Q driver having an interesting ribbed surround. Of the three bottom 8" woofers, only one is powered with the other two being passive radiators (or what KEF calls Auxiliary Bass Radiators). This allows the Q900s to forgo the usual port while still maintaining a bass reflex design. "

( taken from : KEF Q900 Floorstanding Speaker Video Review | Audioholics )

Might be very helpful if you do a full fledged search on the Net . I paid Mission about Rs 6000/- for 2 small 5 inch drivers a few years ago ( without shipping). 10K for a new (imported) 8 inch driver plus labour sounds very low.

Better you check things out with help from the Net.
Contact KEF and explain your problem " very clearly ". See what they have to say. Unless it is a standard problem it might be hard for them to actually give you a perfect solution without seeing your speaker.

http://www.kef.com ( just go to support or 'contact' them )
Ask them for the circuit diagram of the crossover.
This should be your first step . Meantime collect more info from the Net.
Don't rush into the repair. If you don't know what you are doing , you could screw it up. So learn it up from the Net and people who can help. It 'could be' something simple.

Note that the bass driver will move excessively if played outside the box ( in open air). This is normal. The ABR's shouldn't move at all if the bass driver is removed from the cabinet. Keep the volume down to avoid physical damage.

I just noticed that you have a pair of screw in 'connectors' at the back for bi-wiring. When screwed in, it connects the UniQ driver and the bass driver together. So surely the top driver has it's own enclosure.
Now if for some reason the black screw tops have been unscrewed the two drivers could be disconnected. Might be a good idea to put it in bi-wire mode ( unscrew the black connectors ) and connect the amp to each pair of terminals separately and confirm the separate drivers work or not. If you have removed the 8 inch bass driver already , you can connect any 1.5 volt battery ( it's safe ) to it's terminals and see if the cone moves in or out ( it will move only in one direction). Might be a good idea to disconnect the bass driver from the crossover by removing at least one terminal connection. It should move , otherwise it means there is some problem with that driver.
 
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doc_sreenu

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Thank you respected members for providing suggestions,

Yes sir as you said, there are passive radiators and one UNI Q driver and one active bass driver.

i have not dis assembled any passive radiators.
you are right sir - in saying that the UNI Q and one passive radiator are in separate enclosure.

now the issue is how to test the driver whether is is working or not.

should remove the soldred part and then test?:sad:, which am not an expert in,
but am willing to learn and do - if this is required.

kindly guide me in doing the same.

regards,

srini
 

Fantastic

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I already explained that. Unscrew the two black knobs on your speaker terminal plate at the back of the speaker. This will disconnect the bass driver from the UniQ driver. Connect the amp to the top terminals and play some music. If the UniQ produces sound it's OK. Then connect the amp to the bottom two terminals. If the woofer is OK it will produce sound. If not you will get no sound.
If you don't , remove the driver and test it with a battery as I have explained earlier . If it is OK then something is wrong in the crossover. If not , then it could be even as simple as a torn leadout from the cone to the speaker terminals.
If you know nothing about speakers and you are just experimenting , better get someone who knows about such things. If all that's difficult or too much of a problem , better pay 10K and get it fixed !
 
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