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Monday, December 18, 2017

Beogram 8000: Replacing the Old Capacitors

The electronic circuitry in the Beogram 800x turntables is for turning the record platter and controlling the tonearm. The audio signal that the turntable produces goes directly from the phono cartridge to a muting relay, then out to the phono cable. Other than the switch contacts in the muting relay there are no other electrical components involved.

The majority of operational problems with these vintage Beogram 8000 turntables are due to failing electrical connections (i.e. solder joints at connectors) and failing electrolytic capacitors.

As I normally do I will replace all electrolytic capacitors above 4.7uF with high reliability, 105°C, Japanese capacitors (Nichicon or Panasonic). On capacitor values 4.7uF and below I like to use WIMA polyester capacitors.

Because I have the floating chassis out on my workbench for the tonearm repairs I replaced the two electrolytic capacitors there first.

Here are the two new capacitors. One electrolytic (47uF) and one WIMA MKS (1uF).

Now on to the microcomputer board. There is only one capacitor there but it is an important one for the microcomputer 5V power. When I opened up the metal box housing this board the heat sink compound lifted the microcomputer right out of its socket.

The old compound was pretty much dried out. Well, this saves me a step in removing the microcomputer IC. I resolder the pins of this socket to the board anyways so I like to change out the IC socket with a modern one. It is also much easier to change out the lone electrolytic capacitor with the microcomputer IC out of the way.

Here is the other side of the microcomputer PCB with two thirds of the contact pins de-soldered.

With the socket and C28 capacitor removed I can easily install the new parts.

Here is the microcomputer IC installed in the new socket. I will wait to apply new heat sink compound until after I have completed and tested the rest of the recap work.

Moving now to the main PCB recap. Here are the component and trace sides of the board before the recap.

The Beogram 8000 went through a number of modifications after it went into production. That is evident by the additional two small boards bolted to the main board, various jumper wires and added components on the trace side.

I started the main board recap with the two 1uF electrolytic capacitors on the trace side. I replaced them with a couple of WIMA MKS capacitors.

I recapped the two add on boards next.

The rest of the main board recap is straight forward other than the large 2200uF capacitor (C27). That capacitor has a special three-prong base for the negative lead that helps support the mounting of the component. I always pry the base off and re-use in on the replacement capacitor. A little hot glue secures the new capacitor to the borrowed base.

Of the three large power capacitors, C24 was completely dead. At least half of the original capacitors were out of tolerance. This Beogram definitely needed this restoration. One other task on the main board was to resolder all of the mounts for the board connectors.

The only electrolytic capacitor left to replace is the 39uF capacitor (C1) in the transformer box. I didn't realize until last weekend that I had run out of the nice Beolover replacement assembly for the C1. I can install a temporary replacement until the permanent replacement assembly arrives from Beolover.

Tomorrow I will hook these Beogram modules together and check out the results of the electronic restorations.

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