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Thursday, November 17, 2016

Beomaster 8000: Repair of a Damaged In DIN7 Phono Jack That Had Lost All Four Panel Mount Tabs

One of the weak spots in Beomaster 8000s are the phono jacks in the input box under the control panel. The plastic of these jacks becomes brittle over the years, and all it takes to break out the plastic tabs that hold the jack above the input box panel is a firm push to get the DIN7 plug from a Beogram into the jack. And then the jack is inside the connector box, and the cable probably not even connected. And this is how this sorry outcome looks like:
Usually, only the top (outside) tabs break off, and there is a fix for this with two 3D printed inserts that replace these tabs. A detailed report on this repair and a video is posted here. This shows the tabs that I installed in this Beomaster:
These tab replacements are available to other enthusiasts via the Beolover Shapeways store. By the way, they also repair the jack on Beocord 8000 and 9000 units. They are also often broken out.

Unfortunately, this Beomaster's DIN7 jack posed a new challenge: It's inside tabs that hold it below the panel (so one can pull the plug without dislodging the jack) were also gone.

Since the original jacks are impossible to find these days, and even replacements from donor units are very hard to come by, I had no other recourse than trying fixing this with yet more 3D printed parts!

But first I needed to repair several disconnected leads, which probably were a casualty of a previous repair attempt. Several jumpers were broken off:
Luckily, while repairing the contact box of another Beomaster 8000 I made an extensive sketch of all the wire connections in this box, and so I was able to restore the connections without trouble:
After this I designed the replacement tab for the right side of the jack. Since it is pretty much impossible to print flexible precision parts on this size scale, I resorted to a two-pronged approach, where I first designed a static tab without spring force that would be glued onto one of the sides of the jack. This would allow to insert the jack diagonally into the cutout together with the outside tab replacements. Then, once seated, the plan was to glue another static tab into the other side of the jack from the inside of the box.

Alright, that was the plan...and here is the execution:

This shows the right side tab:
It fits into the side 'cavity' of the jack that is shown here:
This shows the part seated (with a dab of epoxy underneath):
I clamped it for an hour until I could be sure that the epoxy was fully hardened:
Then I inserted the jack together with the top tabs:
The next step was to design a tab for the other (left) side of the jack that I could get into the 'cavity' from the inside of the connector box:
I made it considerably longer than the other one. This gave me enough 'meat' to handle it on the inside and guide it into the space between jack and panel. I put some double sided tape on the contact surface and then inserted it into the space:
The part fits very snugly, and my hope is that the double sided tape will hold it in place reliably once pressed in. This will allow extracting the jack again if necessary in the future, in case there are further repairs necessary etc...I always thrive to make my repairs and updates 'reversible' in case a better solution comes along in the future.

The tight fit required me to use tongue and groove pliers adjusted to fit the task:
And this is how it looked after the repair was completed:
Almost like new! Beolovely! I gave this assembly a bunch of plug-in and -outs with a tight fitting DIN7 cable, and it seems to hold up nicely. But I will recommend to my customer to hold the jack down while pulling out the plug. Looks like we are getting close to buttoning this baby up and giving her a first spin!

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