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.

Beocord 5000 (4716/4715): Removing the Drive Mechanism

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Note: This post is 'historic'. There is a much easier way to extract the drive from the enclosure without lifting the Pre-Amplifier board (PCB #1) and removing the solenoid linkage as is described here. Check out my subsequent post about this process, which discusses the updated procedure.
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Per advice by 'chartz' and 'sonavor' of Beoworld.org (here is a link to the thread) I started working on replacing the belts of my Beocord 5000 (4716), which are all out of spec...they expanded over time and have too much slack. 

The first step is to take the drive mechanism out. In order to do that one needs to first flip up the board on the left to be able to get to the solenoid linkage. Chartz suggested to bolt the operating panel in reverse orientation back to the bottom of the enclosure with three screws. A great idea! This helps preventing breaking leads off when manipulating the expanded mess. Here is a pic:

The next step is flipping up the board on the left. This board is held in place by one screw in the back right corner, as well as a screw into the bottom of the enclosure next to the red DIN socket in the front part of the board. After removing the board one can move it a bit to the right to pull it out of the slits in the two brackets on the left that hold the board in place. 

A great thing is that there are two more slits that point upwards where one can secure the board in upward orientation. At this point it is a great idea to protect the plexiglass cover with an old T-shirt or the like from scratches. In my pic this was not implemented yet, as I was still ramping my learning curve...;-):

So far so good. Now it was time to get the drive out. 

The first step is to remove the solenoid linkage:

This requires removing the retaining ring that holds it on the shaft it pivots on. This requires a retaining ring removal tool. since the ring is seated flush with the linkage, this is a bit painful: I was able to get it off unscathed by carefully prying it open with the retaining ring tool, while jamming a small screwdriver in-between the ring and the linkage, thereby pushing the ring up. This enabled me to get the tool further in, which then allowed me to remove the ring just by prying it open and moving it further upwards.

Once the ring is gone, the linkage can be rotated 90 degrees, and removed:

the next steep is to remove the plug that connects the heads (make sure that the deck is unplugged when the plug is pulled to prevent magnetization of the heads - not sure why, but that is what it says on the half-obscured small print warning label in the operating panel - obscured and small print: that is how warning labels should be..;-):

After this I unsoldered the solenoid connections:

The drive is held at the front by two screws that go in from the bottom of the enclosure into the solenoid bracket. Here is a picture from below the enclosure:

These screws needed to be removed or just loosened that the drive can slide forward.

In the back there is no screw that holds the mechanism, only a bracket that fits into a slit in the mechanism. By sliding it forward the drive can be lifted out.

Almost done. The last step was to remove the large wire to board connector from the back of the drive:

This connector sat fairly snugly, and I had to carefully pry it loose with a small screwdriver from the side, and then pull it downwards. At that point I wished I had taken out the plexiglass cover for better access, but finally it came loose, and the drive was liberated.

Here is a pic of the drive after I took it out:

And the 'cavity' left behind in the enclosure:

That is it for today...next step is to partly dismantle the drive mechanism to get at the belts.

Beocord 5000 (4716/4715): First Contact

It did not take long, and I got restless after enjoying the Beomaster 6000 for a couple of evenings...I had to open up the non-working Beocord 5000 (4716) and have a look at its inner workings. A pretty cool design. I really appreciate the 'electronic' VU meters done with 7 incandescent light bulbs each...back then that was the forefront of technology! Incredible! Love it! What an effort! Here are a few pics:

Plexiglass cover off:

Note the two red fold above the level pots...they indicate the recording level! This is just awesome!

Unfolded:

And a detail shot of the VU meters from the back. Each bulb is driven by a transistor...discrete bliss!

Seems I definitely need new belts for this one...there are four: Two drive the tape deck and two thin ones seem to be in charge of the counter.