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Sunday, January 6, 2019

Beogram 8000 Type 5613: Recapping the main board and microcomputer board

The capacitor replacement on the main board and microcomputer board is complete. The microcomputer board also got a new socket for the microcomputer IC and the solder joints were reflowed on all of the board connector pins.

Here is the start of the main board recapping.

A nice small board plus three smaller boards. It should be pretty easy.

That's what I always think but it turns out this board takes me longer than any other Bang & Olufsen board from the period. You have to disassemble the two add on boards and the microcomputer board is difficult because there is so little space to get to the single capacitor on it.

There are two small 1uF capacitors on the trace side of the main board so I will do those first.

One got nicked but is okay.

The main board recapping goes pretty quick until I get to the largest capacitor, C27.

The original C27 is attached securely to the main board by three mounting pins which are connected to the negative side of the capacitor plus the single positive lead...four mounting points. New, replacement electrolytic capacitors don't come with the same mounting options (or at least I haven't found any) and I don't like the way the two lead replacement capacitor is wobbly using just the two mounting points.

My solution is to pop off the original C27 base (with the three prongs) and use it on the new capacitor. I solder the negative lead to the base then put a bead of black hot glue around the edge.

That makes for a good solid fit.

That takes care of the main board (and the two, small add-on boards).
On to the microcomputer board.

The microcomputer board only has one capacitor...C28. Only one but it is difficult.
Its positive lead is soldered to the trace side of the board while the negative lead is soldered to component side of the board. The proximity to the microcomputer IC makes it a little risky so to be safe I don my anti-static strap, ground the metal box containing the microcomputer board and remove the microcomputer IC.

On this particular unit the small add-on board inside the box gets its power from the C28 capacitor directly across the C28 leads. That adds to the removal difficulty.

Since I removed the microcomputer IC for safety I always go ahead and replace the 40-pin IC socket. Removing the socket also gives me more working room. The new replacement socket is a heavier duty socket.

With the microcomputer IC and socket removed I am able to get my soldering iron on C28 to remove it.

For the replacement C28 I will run both its positive lead and the positive power wire (red wire) from the add-on board together to the trace side.  The C28 negative lead also goes through the PCB but does not have a solder point on the trace side.

The add-on board negative power wire (black wire, ground) solders to the C28 negative lead and the ground solder pad on the component side. You can see how having the microcomputer IC and socket make that a much easier task.

Now the new microcomputer socket can be installed.

Here is the completed microcomputer board along with the main board. I won't attach the lid to the microcomputer board box until I make sure the Beogram powers on and works.

Once I verify the recapped boards are good I will be able to start in on the service manual checks.

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