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 Betreff des Beitrags: L710 crossover
BeitragVerfasst: 10.10.2017, 06:13 
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Jungspund
Jungspund

Registriert: 04.10.2017, 20:38
Beiträge: 14
Hello!

I apologize in advance. I know this question has likely been answered but my searches haven't been successful so far. I'm looking to replace the two electrolytic capacitors in the L710 crossover. Is there a consensus for the best replacement of the two 50 MFD 35V capacitors?

I've been researching the Mundorf capacitors and there seems to be a few candidates at 47MFD with one "raw" and a few "plain" versions.
I'm concerned the "plain" capacitors will be too big physically. I've yet to access the crossover to measure the dimensions of the original capacitors.

http://www.partsconnexion.com/capacitor ... bipol.html

As a follow up, is it crucial to add a capacitor in parallel to reach closer to original 50MFD or would 47MFD be sufficient?

Thank you!
Jon

Dateianhang:
IMG_0170.JPG


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 10.10.2017, 08:03 
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Registriert: 28.12.2010, 15:36
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Hi Jon,
Norbert has worked on his pair of L710 ~8years ago, as you can read in this thread:
http://www.braun-hifi-forum.de/viewtopi ... iche#p1536
He replaced the capacitors with 47µF-50V which seems to be still sufficient...
Yours,
Gereon

_________________
...meistens ist es was Mechanisches...
- wenn es nicht will, wende Gewalt an;
geht es kaputt, hätte es eh gewechselt werden müssen... :wink:


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 10.10.2017, 18:03 
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Jungspund
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Registriert: 04.10.2017, 20:38
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Hallo Gereon,

Thank you for the link. I really enjoyed reading through that thread.

I'll be sure to document my progress once I start the restoration.

viele Grüße
Jon


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 11.10.2017, 18:16 
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Jungspund
Jungspund

Registriert: 04.10.2017, 20:38
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Hallo!

I thought I'd document my progress for others who are neophytes and want to see the step by step process.

To gain access to the crossover, the back panel needs to be removed. There are 10 Phillips head screws that must be removed:

Dateianhang:
IMG_1380.JPG


To remove the back panel takes some gentle prying but it will eventually come free. There is a black sealant around the perimeter of the case/panel interface. I'm not sure what this sealant is but it looks to be the same that is used for sealing the drivers to the front of the cabinet. If anyone knows what this sealant is please let me know!

With the cabinet open you encounter several pieces of insulation that can be simply removed to discover the crossover.
Dateianhang:
IMG_1382.JPG

Dateianhang:
IMG_1383.JPG


The crossover is secured by two 8mm nuts. Remove those and the crossover can be removed from the mounting bolts.
Dateianhang:
IMG_1384.JPG

Dateianhang:
IMG_1385.JPG


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Zuletzt geändert von SX-70 am 11.10.2017, 18:39, insgesamt 1-mal geändert.

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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 11.10.2017, 18:35 
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Jungspund
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I'm only replacing the two electrolytic capacitors which are 50uf 35volts and measure roughly 40mm long x 18mm in diameter.

I've chosen to go with Mundorf electrolytics:
I ordered both the "raw" and "plain" versions of the 47uf:
Mundorf E Cap 47uf / 35VAC-100VDC, MLytic Bi-Polar AC (ECAP100-Raw), 14mmD x 37mmH
Mundorf E Cap 47uf / 35VAC-50VDC, MLytic Bi-Polar AC (ECAP50-Plain), 25mmD x 38mmH

I would prefer to use the "plain" version but the "raw" is a better match with the original size wise. We'll see what works.

I also ordered a smaller value to place in parallel to get closer to the original 50uf.
Mundorf E Cap 2.7uf / 50VAC-70VDC (ECAP70-Plain)

I'll post more updates when the caps arrive. Any input or suggestions are welcomed! Again, if someone knows what the black sealant is, please let me know.

viele Grüße
Jon


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 11.10.2017, 19:44 
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It seems that some kind of joint sealant in black was used - something you can get at the local building diy store section / Home Depot.
Do not - repeat, NOT, i.e. never ever - use some kind of silicone / polysiloxane.
Silicone is a "wetting-disruptive" (=benetzungsstörend) stuff - you'd never be able to paint / varnish the speaker again (if necessary).

Yours, Gereon

_________________
...meistens ist es was Mechanisches...
- wenn es nicht will, wende Gewalt an;
geht es kaputt, hätte es eh gewechselt werden müssen... :wink:


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 16.10.2017, 18:03 
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Jungspund
Jungspund

Registriert: 04.10.2017, 20:38
Beiträge: 14
Hallo Braun community!

My unscientific analysis suggests that the sealant was most likely composed of butyl rubber. It was applied very thinly and I can see smear marks in places suggesting it was in semi-liquid state before curing to a putty like consistency.

Edit: Nah....it's more like Mortite rope caulk material.

Probably both would work great.

I'm going to go listen to some music!

Best,
Jon


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 16.10.2017, 20:11 
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Braun-Kenner
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Registriert: 19.01.2009, 03:06
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Hi Jon,
type "Bostik" in the search function and you find the answer. The adhesive is called Prestik.

Gruss
Wilhelm


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 24.10.2017, 17:42 
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Jungspund
Jungspund

Registriert: 04.10.2017, 20:38
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Hallo!

Thank you for the tip Wilhelm. That product isn't available here I don't think but I imagine there is an equivalent. The original sealant seems to be very similar to the rope caulk Mortite product.

Update:
I replaced the capacitors and was surprised that the original capacitors all measured around 60uF. I don't have the right device to measure the ESR but I wonder if these caps could still be good? Replaced with single 47uF Plain Mundorfs - fit well and all measured around 51uF. I didn't see a reason to add another in parallel. I used 3M double sided tape to secure the capacitors. (Edit: In the picture it looks like one of the Mundorfs is pushing the adjacent red capacitor over but it was already leaning that way and there is space between).

Dateianhang:
IMG_1410.JPG




Another problem (sorry!)...I think I've encountered a common problem mentioned here:

http://www.hifimuseum.de/braun-l710.html

Dateianhang:
IMG_1408.JPG


In my picture you can see the outer paper support ring, then a little copper ring, and then (on the inside) what appears to be another paper support ring. I'm wondering if there is another copper ring on the inside near the voice coil that requires cutting open the linen covering to retrieve as was described on the hifimuseum site - or is this the only ring that needs to be dealt with? Any suggestions on how to approach this repair would be very much appreciated.

As always, thank you!

Jon


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 25.10.2017, 14:38 
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Braun-Kenner
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Registriert: 19.01.2009, 03:06
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Our speaker expert Rainer Hebermehl asked me to forward the following repair instructions.
The rivets on the speakers are faulty. For better handling you should remove the woofers and cut out the screen covers which you don’t need anymore. You will find loose wires with the faulty rivets and a black grommets. Desolder the wire and remove any remnants. Glue the paper grommet to the outside of the housing, feed the wire through the grommet, connect (solder) to the speaker wiring and mount (glue) to the woofer basket. Make sure there is no connection from the wires to the basket.

Regards
Wilhelm


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 26.10.2017, 06:11 
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Jungspund
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Registriert: 04.10.2017, 20:38
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Thank you Wilhelm!

I will have to repair it properly soon.

I believe the wire is still glued to the woofer cone as it's still functioning (there is no loose/detached wire) but the adhesive for the rivets and paper grommets has failed.

Here is an example from the hifimuseum site:
Dateianhang:
Braun-L710-Chassis-8652.JPG


As a temporary measure I secured the external grommet and rivet with butyl putty externally. Then I reached inside and used butyl putty to secure the internal grommet and rivet to the inside of the basket. I was careful to keep the wire from contacting the basket.

Dateianhang:
IMG_1415.JPG


I'm guessing there originally was a paper grommet on either side of the basket, a metal rivet on the basket side and a metal rivet at the cone. So the metal rivets are not necessary? I think he suggested just removing them altogether.


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 Betreff des Beitrags: Re: L710 crossover
BeitragVerfasst: 26.10.2017, 12:12 
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You are correct, there is one black grommet und one paper grommet on either side of the basket. If the rivets on the basket are still usable please use them again as solder terminals. Do not remove the rivets attached to the cone!

Wilhelm


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