SpeakerTalk Forum Index SpeakerTalk
This forum has been set up to facilitate discussion of 1970s KEF speakers and drive units. The owner of the Forum has no connection with KEF Audio.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Problem with crossover in a Kef104aB

 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers
View previous topic :: View next topic  
Author Message
Murdoch
Introductory Contributor


Joined: 27 Jul 2006
Posts: 1
Location: Toronto, Ontario

PostPosted: Fri Jul 28, 2006 6:53 am    Post subject: Problem with crossover in a Kef104aB Reply with quote

Hey there, this is a first post post from a kef speaker neophyte...

Recently, one of dad's old Kef 104aB's gave up the ghost. I've removed both the SP1039 and T27 SP1032 and they have tested fine (sound emitted when input applied). So I figure a component on the crossover has failed. The unit has a label SP1065; the HF Fuse is intact, and when the input is applied, the audio is faint and tinny (more so in the SP1039, I assume because it take more power to drive?). Anyways, if any of you can give me an idea as to what might be up or troubleshhoting tips, it would be greatly appreciated. Thanks a lot for any help.

Mark...
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Fri Jul 28, 2006 10:16 am    Post subject: Reply with quote

Well the SP1065 circuit can be found here

http://www.hifiloudspeakers.info/Anatomy/Crossovers/104aB/KEF104aBcrossover.gif

and the only components likely to cause problems are a cracked or dry joint on the input leg of L1 (not likely), or the Silver "Acoustic Contour Control" wafer switch contacts being crudded up.

I use a lead with a 3.5mm mono plug connected to 4mm plugs for speaker testing and add crocodile clips for driver testing.
This lead is plugged into the earpiece socket of a transistor radio and I can get quite reasonable sound levels in all cases.

So, both the bass and treble units may have been damaged, for even when running on half a voice coil, with the other half sitting in the pole piece well you'll get some kind of sound out of them.

Off to work for 11:00hrs now Sad .

Best of luck Very Happy .
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Fri Jul 28, 2006 1:26 pm    Post subject: Reply with quote

hi,

If you have a pair, where one is fully working, then you can compare one to the other. First look for mechanical damage or wear; pcb cracks, component or switch damage, components hanging on by one leg, failed inductor ty-raps, oxidised fuse holder, etc, etc.

If everything looks OK and you don't have much test gear (and you can solder) you could swap components, one at a time, from board to board and see at which point the fault moves over from one system to the other. You should be able to isolate the fault that way. Old electrolytic capacitors do sometimes go open circuit and inductors can go short circuit if the wire enamel wears through where the ends overlapif there was not enough tape between them.

happy fault finding
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> KEF speakers All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group