A Pair of Beomaster 1900 Receivers for Restoration: Recapping the Tone Control & FM Tuning Board (Unit #1)

The most time consuming tasks of the Beomaster 1900 restoration were completed in the last post.
This post shows the final board that needs capacitors replaced....The Tone Control & FM Tuning Board.
The capacitor replacement is easy. There are just ten capacitors and they are easily accessible. The difficult task on this board is cleaning and repairing the three slider controls (Bass, Treble and Balance).

Here is the Tone Control & FM Tuning Board before photos.

I started with the the cleaning and repairing of the slide controls.

After some disassembly of the Bass and Treble sliders I could see that an early repair attempt had been made in the past. Probably at the same time the bridge rectifier on the main board was replaced (though the two items are not related).

These slide controls have a weak part of their design and that is where the control contacts mount to the sliding control bridge. The small, black, plastic piece of the bridge the contacts fit into tends to break.
You can see where there was an attempt to repair that problem with some glue on the bridge of the bass control.

Here is the slider control for treble.

A good slider control bridge repair kit was probably not available when the glue repair attempt was made. That repair probably worked for a while. Eventually that type of repair will fail again so the fix made today is to use a replacement bridge that is supplied by Martin Olsen of Beoparts.

This photo shows the new Beoparts bridge next to the original bridge for the bass control slider.

Here are the bass slider control contacts mounted on the new bridge

Another task of the slider control repair is cleaning and lubricating of the rails the contacts mate with.

I use some Deoxit and some conductive carbon grease. This bass control slider is ready for reassembly and installation back on the Tone Control & FM Tuner Board.

Here is the treble slider control ready for reassembly.

I am starting to get anxious to listen to this Beomaster receiver.  Still a little ways to go though.

The third and last slider control, the balance control, is a different style of slider. It looks similar to the others but its construction is such that it does not require the repair that the bass and treble controls did. I prefer this style of slider that the balance control has. It seems to be more durable.

It does require cleaning and lubrication though.

Here are the before and after photos of the cleaning of the balance slider control.

Now for the capacitor replacements.
Like the other electrolytic capacitors in the Beomaster these were out of tolerance.

Here is the worst one, a 2.2uF capacitor.

Wow... 6.27uF.

Here is a photo of the restored Tone Control & FM Tuning board.

The final restoration tasks before testing the results is to replace the Beomaster 1900 indicator lamps.
I will do that tomorrow.

Beomaster 2400 Type 2902: Tone controls slider bridge repair

A common failure on the Beomaster 1900 and 2400 receivers is with the tone control slider assemblies. Each slider has a left and right channel contact that slide up and down together on a plastic bridge. The contacts are press fitted onto the bridge and held by a plastic post and bar. Over time the plastic bar breaks and the contact comes loose. That results in the slide control no longer working.

Martin Olsen on Beoworld makes replacement slider bridge kits specifically for the Beomaster 1900 and 2400 units. I have used his kit on all of my Beomaster 1900 restorations so far and will continue with this Beomaster 2400 unit. The replacement bridge parts have a beefier bar for the contacts to mount to than the original part.

Here are each of the three tone control sliders disassembled from the tone control board starting from left to right with the Bass slider first.

As you can see the Bass slider has the usual broken tab but it also has a problem where one of the contacts is missing.  I did not see it anywhere in the Beomaster cabinet so it is long gone.  Fortunately I have a spare.

Next is the Treble slider.

Both left and right channel contacts are present with the Treble slider but its slider bridge tabs are broken.

Last is the Balance slider.

The Balance slider has its slider bridge all intact.  I will still replace it along with the Bass and Treble sliders as this slider control is likely to break in the future.  Martin's repair kit comes with three replacement bridges so I will use all of them.

Besides replacing the slider bridge I clean the metal contacts and the rails.
The repair for all three slider control bridges is the same so I will just show one in detail here.

...and here are all three slider controls re-installed on the Beomaster 2400 Tone Control board.

Beomaster 2400 Type 2902: Recapping the tone control board and FM tuner

To wrap up the capacitor replacement on this Beomaster 2400 restoration there is just one capacitor in the FM tuner box and a handful of capacitors on the tone control board.

The FM tuner box has top and bottom lids that must be removed. There is a shield wire that must be desoldered from the bottom lid before it can be opened. The bottom lid is necessary to desolder the lone 10uF capacitor leads.

Under the top lid we can find the capacitor that will be replaced.

...and here is the recapped version

The last board to recap is the control board for the tone controls and FM tuning. There are just ten capacitors to replace.  Here is the before and after picture.

I am not finished with this tone control board yet. The next task is to remove the Bass, Treble and Balance slide control devices to rebuild them.

Beomaster 1900 Type 2904: Capacitor Replacement Part 2 and Slider Control Repair

All of the electrolytic and tantalum capacitor replacement tasks are complete now on this Beomaster 1900 project.

The last board was the tone control and FM tuning board.

There are are only eight capacitors to replace on that board. Here are two before pictures.

...and here are the after pictures. Very straight forward.

The larger task on this board is the repair of the three slider controls (bass, treble and balance).
It is very common for these controls to fail on the Beomaster 1900. The failure is mechanical and involves the plastic slide that holds the left and right channel contacts for the respective control.

A small plastic tab that holds the metal contact in place breaks and the contact becomes free to move around. This results in faulty or no sound in one or both channels.

I noticed at least one loose contact when I did my initial assessment of the Beomaster. To be sure of the condition of all the sliders they must be disassembled and checked.

It is a good idea to label the slide controls as they are removed from the board.

Two small, metal tabs on the end of the control must be bent straight so the metal clamp/holder can release and allow the contact slide mechanism to be removed.

Here are all three sliders disassembled. I found three with broken contact mounting tabs.

The repair for this problem is best made using a repair kit from Martin Olsen. Martin makes a number of  accurate replacement kits for various vintage Bang & Olufsen components that he sells on his Beoparts website.

In this case the kit consists of three replacement (plastic) slider control parts plus some useful instructions.

I cleaned the metal contacts and slider areas with Deoxit (cleaner and fader lube). Then I reassembled the slider controls.

 

Next up are the lamp replacement tasks.