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Friday, September 15, 2017

Beogram 8000: Replacing Capacitors On The Main Boards

Restoration work on this latest Beogram 8000 project begins with the main boards. I will replace all of the electrolytic capacitors with new, high quality, Japanese 105°C capacitors. Most of the time I use Nichicon, Panasonic or Elna capacitors. Where possible though I use WIMA polyester capacitors where capacitance values are 4.7uF or less.

Here is the main board with the microcomputer board and two small B&O mod boards attached.

The most time consuming PCB work is on the microcomputer PCB. There is only one electrolytic capacitor on that board but it is in a difficult place. Here is the microcomputer PCB opened up.

The 47uF (C28) capacitor has its positive lead soldered on the trace side of the board while the negative lead solder point is on the component side of the board. This capacitor is for the +5 V power supply to the integrated circuits on this PCB.

 I usually replace the microcomputer IC socket while I have that board open. The original socket is not as rugged as the modern socket I replace it with so it is a good upgrade.

Here is the microcomputer board with its new C28 capacitor and microcomputer socket.

NOTE: Because the microcomputer IC had to be handled I made sure to wear an anti-static (ESD) wrist band.

Now it is on to the main board. I start with the three largest capacitors - C27, C24 and C29.

Old audio components usually begin to fail due to one or more key electrolytic capacitors failing. I find that most of the capacitors are still within their tolerances but there are always some on the edge of their limit or failed. That is the reason we go ahead and change them all out during these restorations.

On this Beogram the C24 2200uF capacitor had failed where it is way out of tolerance. It should have measured over 2000uF instead of just 475uF.

Quite a few others were also out of tolerance or on the edge of their limit.

The original C27 capacitor came with a three prong base to secure it to the PCB. This base is not found in modern replacement capacitors so I snap the original base off and re-use it with the new C27 capacitor. This makes for a good fit and I put a bead of hot glue around the base to secure the capacitor more than just the soldered on negative lead.

When I removed the original electrolytic capacitors and started to replace them I noticed that three of the black press-to-fit board connectors had deteriorated and were damaged (shown outlined in the next photo).

I always re-flow the solder on the board connectors anyway so after I finish recapping the board I will replace those damage connectors with some I have from a spare Beogram 8000 main board.

Here are the main board, microcomputer board and mod boards after recapping.

I will reflow the connector solder joints next and replace the damaged connectors. After that I will recap the motor capacitor in the transformer housing and the two capacitors that are mounted on the Beogram floating chassis. Once all of that is completed I will be able to test the Beogram electronic operation.

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