Beomaster 2400 Type 2902 - Canada Project Capacitor Replacement Part 2

Wrapping up the Beomaster 2400 capacitor replacement is just recapping the tone, filter and FM tuning board. Just eight capacitors on this board. This board also has the three slider controls that I cleaned with Deoxit fader lube. 

Here is the board before replacing the capacitors.

Here is the board after the recap. As with the other boards, the seven electrolytic capacitors were way out of tolerance (50% to 100% off their value). The lone 0.22uF tantalum was fine but in being consistent with my other replacements I replaced it with a WIMA MKS capacitor.

All total, there were 58 electrolytic capacitors and 19 tantalum capacitors replaced in this Beomaster.

Beomaster 2400 Type 2902 - Canada Project Capacitor Replacement Part 1

 I got through all of the work replacing old capacitors in the Beomaster 2400 main board (over 60 capacitors) and volume control board (2 capacitors).

Here is the Beomaster 2400 again prior to replacing the electrolytic capacitors.

This restoration was different than my usual Beomaster 2400 capacitor restorations.
The owner of this Beomaster had already purchased a Beomaster 2400 recapping kit from Martin Olsen.  It has been a long time since I used someone's capacitor kit but why not? The capacitors are good capacitors so I wouldn't want to waste them.

Martin's kit also included a new bridge diode for the incoming AC power so I will replace that.
This kit has all of the replacement capacitors for the Beomaster 2400 electrolytic capacitors except the two large 5000uF, 50V reservoir capacitors so I will add those two.

The kit also does not contain replacements for the Beomaster 2400 tantalum capacitors. The tantalum capacitors are typically still okay but I normally replace them as the restored audio component often has a long trip back to its owner. Replacing them is a bit of additional insurance to avoid having to send a problem component back and forth.

Of course you will find a lot of discussion on various audio forums about whether to replace tantalum capacitors with tantalums or a different type like electrolytic or polyester.  For capacitance values of 4.7uF and smaller I prefer using WIMA MKS polyester capacitors so that is what I will be doing here.

Here is the Beomaster 2400 after the recapping task of the main board and volume control board have been completed.

I also replaced the left and right channel no-load current adjustment trimmers with new multi-turn, sealed type trimmers.  There were three capacitors, the black ones in the photo, that were capacitors that had been replaced by someone else previously.  They measured good but I changed them so that all of the capacitors starting with this restoration are the same age. One thing to note...one of the previously changed capacitors was 33uF instead of the original 22uF capacitance value.  Martin's kit calls for the original 22uF capacitor which is also what I have always used. I have no idea why the 33uF was put in here.

For my own knowledge base I always take a little extra time and measure each capacitor I remove. I just want to know what state it is actually in.  On this Beomaster 2400 all of the electrolytic capacitors except the large ones were out of tolerance. The 1uF capacitors almost all measured over 2uF. The 2.2uF capacitors were either at 3.5uF or just over 4uF.  The 4.7uf were around 6uF. 

The tantalums were all still within their 20% tolerances but a lot of them were close to the upper limit.

The reservoir capacitors measured good but I still always replace them to insure against future problems.

Here are the two reservoir capacitors before replacing them.

Here is the after photo.

 

The reservoir capacitors are a little tricky to change. B&O connected a number of ground wires to the common point of the reservoir capacitors. The positive and negative DC connection points each have three wires connected as well. New power supply capacitors I use have small posts so connecting the number of wired the Beomaster requires means creating some good terminal solder points.

I joined two terminal posts together for the ground wires and soldered all of the ground wires to that ground terminal. I soldered the positive DC voltage wires to another terminal then soldered that to the positive post of the reservoir capacitor assembly. I also connected the negative DC voltage wires to a terminal on the negative post.

That makes for a really solid reservoir capacitor assembly and the wires are neatly connected.

Two of the black ground wires go to the speaker jacks.  The original wires are short and don't have much room to operate with.  One usually always breaks off when raising and lowering the main board during the recapping process. I always replace those with some longer wires that can handle the main board raising and lowering.

Here are the before and after photos of the volume control board.

Here is a photo of the two new multi-turn, sealed trimmers that will be used to adjust the no-load current of the output amplifiers.

The adjustment knobs for the trimmers are easier to access than the old trimmers.

The next restorations task is to do the capacitor replacement on the removable board with the tone controls, filters and FM tuning.  That will be followed by cleaning the slider controls and the replacement of the lamps.

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.