Beomaster 2400: Recapping the Main Board

Whew! The main board of this Beomaster 2400 is fully recapped now. Seventy capacitors were replaced and there are still a couple of boards left that also need recapping.

Here are a couple of photos of the main board after the recap

The bulk of the restoration work was on this main board recap.

Now let's go back to the start of the recap and look at some of the details.
Here is the board before any of the capacitors were replaced. There are three metal shield boxes on the main board. Each shield box houses one capacitor that I needed to replace. The three metal boxes are highlighted in the picture below. The box in the top right is for the FM Front End, Tuner. The box below it is for the FM Detector. The third box just to the right of the Beomaster 2400 reservoir capacitors is for the remote control receiver.

For me the best way to do the recapping is to just systematically go through and replace each capacitor one by one. I tried removing a bunch at one time then spent a bunch of time rechecking the work to make sure polarities and capacitance values were correct. Doing them one at a time and keeping track of the polarity as each capacitor is replaced is a much safer way to go.

Looking inside each of the metal boxes we find the following.

I found that almost every capacitor, except for the reservoir capacitors and tantalum capacitors, was way out of tolerance. A lot of the capacitors were almost double the capacitance they were supposed to be.

The 10uF, 63V electrolytic capacitor inside the detector box measured over 20uF...and so did all of the other 10uF, 63V capacitors on the board.

The 10uF, 10V tantalum inside the Front End, Tuner box measured okay but I still replace it as I already planned to do in this full capacitor restoration.

The remote control receiver box also had a 10uF, 63V capacitor that measured over 20uF.

The Beomaster 2400 has a small "mod" board installed by Bang & Olufsen at some point in going from the Beomaster 2400 Type 2901 to the Beomaster 2400 Type 2902. The board changed components used for the tape record audio signal and has four capacitors that this recapping exercise replaced. The small board had to be de-soldered from the main board so the trace side could be accessed for the capacitor replacement.

There are three power supply reservoir capacitors that I replaced.
One reservoir is a 2200uF, 25V electrolytic capacitor that is used in the +15VDC supply.

The other two are 5000uF, 35V electrolytic capacitors for the ±31VDC rails used by the output amplifier section.

I replaced the originals with 5600uF, 50V capacitors. They each measured around 5200uF which is nicely in the 20% tolerance of the original value.

As I mentioned earlier, most of the capacitors on the main board were badly out of tolerance.
Here are some examples of what the old, original capacitors measured as I removed them.

The main board is where most of the restoration work takes place on these Beomaster 2400 (and 1900) receivers. I still need to replace the two trimmer resistors on this main board for the Left and Right channel no-load current adjustment. I will finish recapping the last two boards then do the trimmers.