On another post I discuss my new to me Kef Reference 104/2s.  The speakers were behaving flawlessly, but then on the third day, after about an hour of use, (playing vinyl) the R speaker stopped putting out sound, except for a very slight bass noise if I put my ear right up to the speaker.  I swapped speakers around, and the problem followed the speaker, now in the L position.  

I reinstalled my Mission 753s, and they played flawlessly.  Put the Kefs back, and now the weird bit starts.  

My Plinius 8150 doesn’t really have enough inputs for me, especially since I stopped using the MC phono input in favour of using a PureAudio Vinyl phono Pre.  So, CD player to cd input, phono pre to Tuner, Satellite receiver to Tape 1 in, Bluray player to Tape 2.

With the Kefs back, suspect speaker back in R position, on all inputs other than cd, there is no sound from the R speaker, but when I played a cd, perfect sound from each!  

Which raises a question, are all these line inputs equal in quality?  Is the cd output higher than the others?

Left for a couple of days, and today, being home alone, I was able to have an extended session playing LPs - surprise, the Kefs behaved flawlessly, and  sounded better as they have warmed up!  The only change I made re the Kefs, was when I was moving them around i noticed the screw in/out levelling feet were loose.  I laid the speakers on their sides and tightened the feet up.

Initially I surmised there was a problem with the crossover in the R speaker, as it is known that capacitors in the crossover on these circa 30 year old speakers can go out of spec.  However, it is a mystery to me, and wonder if any experts here can shed some light on it?

That sounds a bit like a loose connection inside somewhere.

I would open the offending speaker up and check that all the lines to the woofers are ok.

Still all working only when using the CD as source input?

DarkLantern blog - darklanternforowen.wordpress.com

Another clue; have just been doing some focussed listening. I became increasingly convinced that the sound from the L speaker was not as loud as the R. Most of the backing music (I.e. on the cd of The Travelling Wilburys) is coming from the R speaker, although the singer is clearly focussed mid stage

I looked back at my notes. The suspect speaker is in the L position.

I then swapped speaker cables around from the amp - L to R and vice versa.

Once again most of the backing music is coming from the R speaker, and the singer remains centre stage.

I think that means only some of the signal is getting to the L speaker. Am becoming increasingly convinced it is a crossover problem.

That the speaker started working again after you had tipped it over to tighten a screw points to a possible loose connection, so I would still suggest a check and clean of all non soldered connections first, they are old speakers and a loose or dirty connection can cause strange faults.

No, Owen, working on all inputs now, but with caveat as above, and further to that when listening with speaker outlets reversed, I was hearing info from the R spkr I hadn’t been hearing on the L, and conversely, was missing information from the L spkr that I had been hearing on the R. Mike may be on to the cause. In hindsight, my road is a rough country unsealed road, so may have got bounced around when bringing them home.

Thanks for the input, Mike, will have a look around on the inside in the daylight tomorrow. Fortunately there is a good YouTube clip showing how to do that.

I agree with Mike, it does sound like a loose connection. This video, may or may not give you some help in at least getting in to it. 

Simply re-check swapping of spkr cable connections now, but be sure to swap them only at the lspkr end - in order to confirm that the problem is within one of the lspkrs, not a spkr cable or upstrea.

DarkLantern blog - darklanternforowen.wordpress.com

Apart from checking the integrity of the connections inside the suspect speaker, I’d measure the resistance of each of the drivers with a multimeter. Then compare those readings with the measurements from the other good speaker.
Some faults can be intermittent and time consuming to find. I once repaired a powered guitar speaker with intermittent treble. I suspected the amp as the tweeter measured normally, only to find the amp worked perfectly. One day my friend told me it had failed yet again. I measured the tweeter and finally found it to be almost open circuit.
Perhaps if you’re going to measure the drivers in the Kef, gently prod the cones or dome with a clean finger to move the voice coil and it’s lead-out wires slightly, to see if the reading goes open circuit at any point. (While prodding the cones lightly the meter might give erratic readings, which is normal. What you’re looking for is if it goes open circuit or not.)
I can’t remember if the Kefs have any switches in the crossover..? If so, the contacts inside could be tarnished and need a clean. Also, the wires inside might have quick-connect terminals on them instead of solder. Sometimes the wire crimped onto the quick connector corrodes and leads to increased resistance in the wire.

AMR-iFi R&D

Thanks all, will be starting work on the speaker shortly. Let you know how I get on.
Mijoh, great YouTube clip. Watched another similar clip recently, and on that one the crossover board was more easily reached, attached to the bottom plate. Fingers crossed mine is too!

Removed base plate, oh dear crossover not there! Removed mid range and tweeter enclosure. Checked out wiring loom, no loose fittings, unplugged mid and tweeter wires from the loom, cleaned lugs and sockets with deoxit. Removed plate to access top woofer cavity.

Discover that the foam donuts on both woofers have perished! Checked other speaker - the same. Time for a full refurbishment!

I will remove the woofers myself, but will take them to a specialist to have done. DIY clips on YouTube show it is not that difficult, but with my essential tremor having got a bit worse with age, won’t attempt replacing the donuts myself. Will have to source a donut replacement kit. Available in nz or will I need to go offshore?

Will have to remove woofers to get at the crossover, a fairly major job, so that will have to wait a bit. Will bite the bullet and order replacement caps from Falcon Acoustics UK.

May as well replace the tweeter at the same time. Can a Morel MDT 29 tweeter be purchased in nz?

By 'grommets', do you mean the rubber 'surrounds' or outer rubber 'suspension' of the woofer cone?
Or only the inner doughnut foam rubber ring?
Either, get them done professionally - see Audiomark in the Useful Contacts section of our homepage.

Are you referring only to the inner (twin) bass drivers?
They are structurally connected & removal will be a tricky job I suspect.

Caps - I'd suggest possibly cheaper & better to source more locally - say Sound Labs Group in AU.
Or HiFi Collective UK.
However, I believe that there are 30+ caps in each of these!?

DarkLantern blog - darklanternforowen.wordpress.com

Apr 10, 2019 12:11:42 GMT 12 Owen Y said:

By 'grommets', do you mean the rubber 'surrounds' or outer rubber 'suspension' of the woofer cone?
If so, get them done professionally - see Audiomark in the Useful Contacts section of our homepage.

Are you referring only to the inner (twin) bass drivers?
They are structurally connected & removal will be a tricky job I suspect.

Caps - I'd suggest possibly cheaper & better to source more locally - say Sound Labs Group in AU.
Or HiFi Collective UK.
However, I believe that there are 30+ caps in each of these!?

See last pic in my post above, what are commonly referred to as “donuts” are the foam inner seals on the bass drivers.  The photo shows the donut broken away from the central post with only bits of it left attached here and there.  The outer surrounds of the bass drivers appear to be rubber and gentle touching reveals they are still intact.
According  to my on line searches, there are 16 (or is it 15 - will check later) caps per crossover.  Falcon Acoustics UK advertise matched sets to Kef specs, at either 2% or 5% tolerances.  
Will check Soundlabs and Hifi Collective, thanks.

Have talked to Kelly at Axent. They have the donuts in stock and can do the necessary repairs. He also suggested, that instead of replacing all the caps on the crossovers, that they can test each cap and only replace those that are no longer up to spec. Seems sensible to me. Had considered removing the woofers and crossovers myself and taking them in for servicing, but they would still want to install and make sure that everything was working properly.

I did send an email to Audiomark, but no reply as yet. Also checked out Soundlabs, which have an online store - HifiOnline, but a search of products didn’t bring anything up.

I have asked the seller to contribute half the cost of repairs! For replacing the surrounds, Kelly gave a ball park figure of $400 - $600, with the upper price being if they had to replace the outer surrounds as well..

The measurements on the midrange seem ok and the 4 ohm rating of the speaker would have the 2 midrange drivers connected in parallel. The total impedance is then 3.65 ohms with the dc measurement of a multimeter. ((7.2 + 7.4) / 4). At midrange frequencies the impedance would be closer to 4 ohms.
Looks like the other drivers are fine.
Did you get around to measuring the connecting wires?
Looks like you can get a 4 ohm Morel MDT29-4 tweeter at Madisound US for US$54 (plus postage, customs etc.)

AMR-iFi R&D

Thanks, Colin, checked the wires for continuity, all good. Didn’t go into the bowels to get at the crossover, so not able to get a read from cab,es there. The positive lead to the tweeter was a bit sloppy where it clipped onto the feed from the xover, so I nipped that up with a pair of pliers. Have t had time to listen yet

sub - since it appears to become (an interesting) a lspkr issue, we might migrate this over to the DIY and/or Restoration section, soon.

DarkLantern blog - darklanternforowen.wordpress.com

Good idea, Owen. Set the speakers back up in the system just now. (Playing Mr Gelb). The L spkr seems to be behaving itself! The balance between L and R appears restored. Must have been something to do with the wiring as suggested by Mike. I used deoxit on all the connections, and tightened the fairly sloppy connection of the +tve tweeter connection.

Mark from audiomark replied, and am waiting an estimate from him.

Would have liked to done the donut repairs myself, but my shaky hands mean I am likely to damage the paper cones. Don’t know why they call it essential tremor, as it is the least essential thing I know of!

Oh, and the seller has made a contribution to the repairs!

Good, sounds like that was all they needed, a bit of TLC inside.

AMR-iFi R&D

Bit the bullet and ordered a replacement set of capacitors from Falcon Acoustics UK. All up price including airmail £80.33, which showed up on my Visa a/c as $160 and a few cents.

Owen, there are sixteen capacitors in each speaker, so 32 in all, The caps are made by Alcap, and said to be to Kef specs. They had run out of sets of 2% tolerance so will get the 5% ones. Should still be ok.

Seller has agreed to pay half cost of repairing the woofer “donuts”, so will organise a trip to Auckland to have repairs done in a few weeks, and after the caps arrive.