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Monday, October 27, 2014

Beocord 5000 (4715/4716): Replacing the Belts

I received the Beocord 5000 belts from 'Dillen' (Beoworld.org). And so I was finally able to continue working on the unit. The procedure is fairly straight forward, but needs some patience, since the drive mechanism needs to be dismantled considerably to get at the belts. Furthermore, there is only a discussion how to get to the belts on the top side of the drive in the service manual, but not how to get to the ones on the bottom. However, there is an interesting thread on Beoworld.org where parts of this process are discussed in some depth. This discussion also contains a bit of a horror story about breaking PCB #3 ('Electronic Switch') in half when trying to get the belt in that drives the counter seated in that board. Anyway, after studying this thread and reading the Service Manual, I carefully set out to do it.

I made a video about the process, which shows most of the steps in some detail (****update: I further streamlined the procedure for extracting the tape mechanism. See here.*****):



After putting the drive back in, it seemed that most of the Beocord 5000 was working. But further testing is in progress.

I thought it was interesting to log the dimensions of the old belts and the new ones in comparison (the numbers refer to the numbers given in the Service Manual, Sec. 4).


Belt
Old ID
New ID
Old Crossection
New Crossection
Belt 119 (flywheels/spools)
3.75”/95 mm
3.3”/84.3mm
0.075”/1.9 mm, round cs
0.08”/2 mm, round cs
Belt 115 (DC motor for flywheels to pulley)
1.86”/47 mm
1.75”/44 mm
0.06”/1.5 mm, triangular, height=base
0.05/1.3 mm, square cs
Belt 143 (Capstans)
(flat belt, thickness ~0.5 mm)
7.6”/194 mm
7.05”/ 183 mm flattened length
0.185/4.7 mm width
0.2” or 5 mm width
Belts 132/135 (Counter)
2.2”/56 mm
2.05”/ 52mm
0.035”/0.9 mm round cs
.04”/1 mm, square cs


The comparison shows that the old belts were quite a bit elongated. Notable are the differences in crossections. The old #115 belt had a triangular crossection, but the square replacement seems to work fine. Same with the counter belts, which were round in the original configuration.





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