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Friday, May 29, 2015

Beocord 9000: Repair of a Broken Out Leaf Spring in the Tape Mechanism

When I opened up the Beocord 9000 that I am currently restoring I found a loose part in the enclosure. The part is shown in this picture on the left:

It turned out that it is the left leaf spring (#12035 in the exploded drawing in the service manual on p. 4-6) that holds down the head carrier. The part on the right is the right spring that I extracted to take a measurement of the ball that takes care of the friction between the carrier and the spring when the heads are pushed into the cassette. The ball of the right side was of course lost...there are many openings in the bottom of the Beocord...

The ball turned out to be a 2.5 mm diameter ball bearing ball. These are widely available. I ordered the smallest batch I could find, which was a lifetime supply of 100 on Amazon.
The black block that is attached to the spring that I found is a broken out piece of the plastic assembly that holds the spring. This assembly is pretty weak, and so it is no surprise that the spring finally cracked the plastic. It is under constant tension.

Luckily it is a straight forward repair to reattach the plastic block and the spring. All that is needed is a 2-56 3/8" screw and a nut and a washer. This picture shows the screw already inserted into the plastic part. The 2-56 screw is tight enough that it threads itself into the plastic part, which is convenient since it allows the fixing of the leaf spring in place before bolting everything together:

Before putting in the screw it was necessary to sand the bottom part of the plastic block down a bit so it would not stick out beneath the hole in the tape mechanism carrier plate into which it fits to hold it precisely in place:

After this the spring assembly can be bolted through the carrier plate. The ball is held in place during the procedure by the grease in the groove (I used a dab of silicone grease). This picture shows the underside of the carrier plate where the sanded round flange fits through the alignment hole:

The next step is to put the washer and the nut on: 

Tightening the bolt while aligning the spring completes the repair. Here are two views of the spring in its place underneath the erase head:

I tested the mechanism after I put it back into the enclosure. Seems this repair did the job.
On to the 7-segment display, which has a missing segment.

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