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Kef 105.2 Crossover / Head Assembly wiring HELP!
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Plett89
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Joined: 27 Feb 2017
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PostPosted: Fri Mar 03, 2017 12:23 pm    Post subject: Reply with quote

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=51749&d=1308403040

Here is a link to the schematics I found online ☺

On the picture of the small PCB, you can see that the brown and the yellow wire shares the same circuit and the circuit goes to the black wire in the plug.
How can this be? If the schematics says that the white wire is midrange . And the yellow is for protection circuit?
This troubles me deeply 😂
I would like to talk to this Colin person. ...
How he could determine these colours.
Thankyou very much for your reply, Speakerguru 😊
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audiolabtower
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PostPosted: Fri Mar 03, 2017 1:10 pm    Post subject: Reply with quote

Colin is no longer with us.

I don't have a Mk2 to look at so can just surmise from your track pictures.

Looking at the pcb tracks the blue wire input goes to the blue wire output and tweeter positive I guess along with the sensing circuit.

The green wire input goes to green wire output and B110 positive I guess along with the sensing circuit.

The black wire input seems to go to the brown and yellow wires output and I guess these go to the T52 and B100 negatives?, which are of course common.

I do not know what the orange and grey wires are but guess they go to the led?

So Colin's diagram seems to be correct in so far as output from the crossover is concerned but does not reflect the colours directly connected to the drive units for the white wire because of the complication of the protection circuit.

You would assume that the black and white would be common from the diagram , but this does not seem to be the case from the tracks, the black is common for T52 and B100 negatives, which would be normal, but the white goes only to the sensing circuit it seems. So I would guess the white "may" be a ground but is used only to feed the sensing circuit and not the drive unit, which would explain your experience with direct amplifier connection.
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Plett89
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PostPosted: Fri Mar 03, 2017 6:27 pm    Post subject: Reply with quote

Thankyou, quite a good explanation and certainly plausible.
I have written KEF a message to ask if they could provide me, with their schematics /diagrams of the speaker, still waiting for reply.

The speakers are most likely wired as they should, because they play beautifully.

It's just Colins's diagram that had me troubled all along. ☺
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pcolafins13
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PostPosted: Thu Apr 20, 2017 1:50 am    Post subject: Reply with quote

i just stumbled across your thread. i have a pair of the 105.2's that i just recently picked up. One of them is tripping off at moderate volumes. I have the crossovers pulled, and i plan to take them to a friend that is knowledgeable at doing this sort of stuff. I'm planning to purchase the rebuild set from falcon. Where is the protect circuit at on the crossover? My crossover looks pretty much the same as the one pictured above.
?
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speakerguru
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PostPosted: Thu Apr 20, 2017 8:37 am    Post subject: Reply with quote

If I recall correctly, the S-Stop board was in the head. The relay which it drives, in the event of an overdrive, is at the input on the main xo board.

Last edited by speakerguru on Thu Apr 20, 2017 5:00 pm; edited 1 time in total
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audiolabtower
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PostPosted: Thu Apr 20, 2017 10:47 am    Post subject: Reply with quote

Yes the switch is on the pcb, so it sits behind the power select knob.
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pcolafins13
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PostPosted: Thu Apr 20, 2017 2:59 pm    Post subject: Reply with quote

I have the crossovers pulled and plan to have a knowledgeable friend restore them with new caps. What are your thoughts about this possibly fixing the s-stop tripping? Should I also have the s-stop caps replaced? I was hoping when I bought these that it would be a fairly quick fix.
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speakerguru
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PostPosted: Thu Apr 20, 2017 5:18 pm    Post subject: Reply with quote

I personally would only replace components which are faulty, i.e. burnt inductors and resistors or capacitors that have changed value.
It's possible that some component failure is creating a resonant circuit which is producing a high voltage somewhere which in turn will trigger the overvoltage protection. However, as the LED is not coming on when this happens, that suggests that it is the S-Stop which itself is faulty.

Check the passive components and the voltage at which the circuit trips out, being careful not to exceed the continuous rating of the drive units in their respective pass bands.

The thick film modules can only be checked by substitution. I think the transistors in the thick film modules were rated at 120V, so, these could have been damaged if the systems were used with any amplifier which could produce more than +/-120 V peak. If the relay driver transistor has gone low resistance or short circuit then the relay would trip prematurely.
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pcolafins13
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PostPosted: Thu Apr 20, 2017 6:14 pm    Post subject: Reply with quote

Wow! Thanks for all that information. It's obvious you definitely know the ins and outs of how all this works. With me being a complete novice it sounds like I may have jumped the gun on purchasing these. It sounds like I would need to take them to a repair shop since I dont know any individuals that have the amount of knowledge needed to Check all of that. I was hoping t would be a quick swap out of some capacitors or something and while at it I was going to go ahead and have all of them done. I will have to think about how to proceed.
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pcolafins13
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PostPosted: Fri Apr 21, 2017 1:12 am    Post subject: Reply with quote

On another thread i started you said that you have a spare pair of S-Stops. I thought I had sent you a Private message regarding that,
but it appears as though it didn't go through. I may be interested in buying those if they are for sale. Let me know please. thanks!
speakerguru wrote:
I personally would only replace components which are faulty, i.e. burnt inductors and resistors or capacitors that have changed value.
It's possible that some component failure is creating a resonant circuit which is producing a high voltage somewhere which in turn will trigger the overvoltage protection. However, as the LED is not coming on when this happens, that suggests that it is the S-Stop which itself is faulty.

Check the passive components and the voltage at which the circuit trips out, being careful not to exceed the continuous rating of the drive units in their respective pass bands.

The thick film modules can only be checked by substitution. I think the transistors in the thick film modules were rated at 120V, so, these could have been damaged if the systems were used with any amplifier which could produce more than +/-120 V peak. If the relay driver transistor has gone low resistance or short circuit then the relay would trip prematurely.
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pcolafins13
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PostPosted: Fri Apr 21, 2017 4:23 am    Post subject: Reply with quote

audiolabtower wrote:
Yes the switch is on the pcb, so it sits behind the power select knob.


http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=657&postdays=0&postorder=asc&start=15

Here is a link to an old thread regarding the same issue I'm having. has anyone confirmed for sure if unhooking the red wire going to the head is safe to do? i am willing to try that if it keeps the protect circuit from activating. The speakers sound fine , and i do not hear any noticeable problems with the woofers. i rotated them when i bought them just incase of the sagging problem.
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