Wednesday, June 21, 2017

made in germany, fixed in usa

In case you wonder, my blog posts have been very photo intensive. I do this for reasons, especially things involves repair and service. I tend to take a lot of photos for future reference. So often that I find that I struggle how to disassemble something, especially products that are made of plastic, only to realize later that I have done this years ago but just cannot remember how it is done without causing irreparable damage.

Recently while carrying out modifications on the Mini I found that the front left side speakers sounded like mosquito singing. Only tiny sound that emits from the tweeter at the top. I decided to invest $2.99 in a set of automotive trim removal tools sold and shipped from Hong Kong.

this would turn out to be the best purchase for $2.99

today is the day to take apart the driver side door to find out what failed; I have already determined it is not the audio head unit or wiring behind the center console

the revised Gen 1 Mini's has this extra step to get to the screw hidden behind the armrest cushion

this wide ply bar is great for popping the plastic snaps

the courtesy light connector

closeup of the slots that engage the metal clips on the top

It has been almost a decade since I installed these MB Quart two way speakers that I forgot the work and time that I invested in a perfect installation

here is the two way crossover and the custom made spacer for the speaker

the tweeter on the top is factory which makes very little sound so I decided to leave it to augment the MB Quart tweeter as it sits very low

When swapping out the cheap factory standard issued speaker a custom made spacer like the one I fabricated is necessary. The stock speaker has an integral plastic spacer which is a part of the unusual speaker made for the Mini front door.

a better detail of the spacer that I made out of 3/4 inch MDF board

When I saw the water residue on the speaker I was bracing for the worst scenario - the water must have gotten onto the voice coil of the woofer and caused corrosion that oxidized the copper winding. But when I checked the resistance it reads normal - almost a dead short. I knew the problem must lies inside the passive crossover.

this is how the crossover I installed connects to the factory speaker harness

I trouble-shoot to the crossover being the cause - you can see the adhesive (most likely superglue) holding the ferrite core of the choke has failed

 I used this bookshelf speaker to verify the speaker connection from the head unit has no problem

obviously the delamination of the ferrite core would not cause the woofer to have no sound - the suspect is the magnetic wire wounding must have severed

here you can see one of the magnetic wire lead has broken off due to vibration as a result of loosing the structure support by the ferrite core

this made in Germany crossover is defective in design; superglue (or similar) adhesive is a very poor choice

I decide to use superglue to glue the three-part ferrite core back together. However I will add a fastener to hold the three part together while the superglue will provide the surface to surface bonding that this magnetic core needs.

I routed out the copper traces around the hole so the stainless steel screw would not cause short circuit

once I checked fit of the screw and nut I apply superglue to the mating surface of the ferrite core

I also apply a dab of superglue to the fastener threads as thread locker

then soldered the choke leads and wires back together

it is now better than new

I considered using plastic or brass screw so not to change the permeability of the ferrite core but decided that the stainless steel screw should have only insignificant effect. Doing otherwise would require a trip to the store. I much prefer to use what I have on hand.

made in Germany - fixed in USA

I am glad the crossover failed. Because of it I found out the speaker location gets a lot of moisture and possible rain water drips so something has to be done.

What should I do to prevent the speaker from rain water and moisture. I was sure I can come up with a satisfactory solution using something I already have instead of go shopping for a automotive speaker condom - LOL.

automotive speaker condom; I actually have a pair somewhere but I just don't feel like go looking for them

I have some remnants of this rubberized dropcloth which is great to use a moisture barrier


I managed to reinstalled the door panel back together without causing any wear and tear. The audio system is sounding great once again. I will wait for a cool day to also check the crossover in the passenger side door and to moisture-prove the speakers on that side.

In addition to the MB Quart 2 way speakers I also have aftermarket elliptical 2 way speakers for the rear channels. Together the acoustic quality is very good.

Update 2017.06.22:
I went ahead and inspected the crossover on the passenger side door, while the remedial process is still fresh in my mind. Also the tube of superglue, once open will dry out very fast and I don't care to buy another pack if I can avoid it.

As soon as I unscrewed the crossover from the door there is the rattle of loose part inside the plastic housing. The failure mode is identical except the two leads of the choke are not broken yet from stress. I performed the exact remedial process, as well as adding the vapour barrier to the speakers.

I never like superglue. It is the most misunderstood adhesive and have very limited applications. Super glue requires perfect machine surface to function, and the surface must be very large. It performs very poorly under vibration and mechanical stress cycles. I have little the crossovers in this MB Quart model has 100% failure rate, given enough time. I wonder is the design failure responsibility lies with the ferrite core supplier, or the designers in MB Quart, or both. Very often a company like MB Quart follows the application note provided by the manufacturer of the part, and this may well be the case.

I considered using epoxy in my repair but doing so requires more work. I decided to use super glue because I am adding the screw and nut to hold the 3-piece ferrite core together.

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