Beovox S45 Repair

[hcraig244]

This arrived in the post this afternoon…..been expecting it, reported as seized….we are all familiar with that issue on these old speakers. The glue that holds the magnet, core and associated hardware together dries up and deteriorates after 40 years, consequently a jolt or knock dislodges the assembly and the core wedges itself off centre gripping the coil firmly.

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[hcraig244]

Came well wrapped up and taking it out revealed nothing untoward, apart from the fact that the cone didnt want to move up or down, also someone had kindly unpicked the dust cap…tricky exercise so I was happy about that ;¬)

• This reply was modified 2 weeks, 2 days ago by hcraig244.
• This reply was modified 2 weeks, 2 days ago by hcraig244. Reason: spelling

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[hcraig244]

I was even happier when I measured the resistance of the coil and it came up a little under the specified 4.0 ohms

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[hcraig244]

Knowing it was loose it was held in a vice by the rear keeper plate and with a quick firm and even lift from the speaker frame the plate and core where left behind…the cone and coil now move freely in and out with no scratchy catching

• This reply was modified 2 weeks, 2 days ago by hcraig244.
• This reply was modified 2 weeks, 2 days ago by hcraig244.

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[hcraig244]

Back on the bench the coil still measures a healthy resistance confirming no damage was inflicted during dismantling, always a worry.

As I dont have sufficient epoxy resin to hand I will have to wait until tomorrow to continue the excercise

Craig

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[pepps]

Looking forward to the next instalment 👍

Location: Kent, UK

[hcraig244]

Ok

Next step is to remove the magnet from the plate that the core is attached to and remove all the old adhesive from all the surfaces, taking care not to break the ferrite magnet in the process….

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[hcraig244]

Decided to try this new (new to me anyway) metal epoxy glue, bit more expensive but gets good reviews. Manufactures claim it sets in 5mins and is hardened after  2 hours…..yeah righto! I will leave it set overnight.

most important thing is to re attach the magnet to the frame the right way around, the polarity is important. The magnet needs to be central to the coil but doesn’t need to be exactly central, the precise centring of the core within the coil is the crucial part of the exercise.

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[hcraig244]

On reflection I’ve decided to use regular epoxy for the fastening of the core and rear plate to the ferrite magnet, this is due to the metal solution manufacturer boasting 5min  adsjusting time along with 2hrs hardening time…..it may take longer than 5mins to align everything and I dont want any pressure ;¬)

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[hcraig244]

Yet again the engineers vice has been dragooned into service, the plate and core are gripped in the vice jaws just below the level of the jaws, about 3mm, the epoxy can then be applied to the plate face and with a very firm grip with both hands on the speaker frame the whole assembly needs to be lowered down onto the upright core, sighting the alignment through the removed dust cap apperture. The magnet is apt to grip the frame violently so a firm hold is required during alignment…..once the core is within the coil the frame can be released to allow it to attach itself to the vice jaws….then one simply unwinds the vice handle and the plate jumps up and into place.

 

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[hcraig244]

moving swiftly on the custom made Jig can be mounted and the upper screws tightened on the ferrite magnet to hold it securely, centred roughly in the middle with the lower set of screws resting on the top of the magnet, then turning everything upside down and viewing the core position through the dust cap aperture the lower screws can be adjusted to centre the core within the coil, this can take 10mins or so as it involves adjusting a screw and its opposite screw to effect the balance.

I have tried the other method using thin strips of card inserted into the coil to centre the core without much, if any, success….my thinking was that speaker manufacturers wouldn’t use bits of card to do this so there had to be a better way.

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[hcraig244]

I will leave this to set hard, checking that the cone continues to move freely all the time, then run a bead of the metal epoxy glue around the entire circumference of both magnet and rear plate to provide additional strength for future knocks. Following the above trauma the coil still gives a resistance reading just below 4 ohms…..

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[matador]

So much memories back…

Location: Paris France

[hcraig244]

The metal epoxy has turned out a little lumpy, which in other applications may be a problem….not with this one however. Dust cap back on with some Aleene’s tacky glue, useful if in the unlikely case it has to be removed again. Ready to be dispatched back home!

Craig

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