Beomaster 1900 (Type 2903): Installing The Replacement Slide Potentiometer Contact Bridges

I have been running the Beomaster 1900 with borrowed parts from a Beomaster 2400 until the contact bridge replacements for the slide potentiometers arrived from Denmark. Thanks to Martin Olsen they were sent right away and got here really quick.

Making the swap wasn't too bad. The board with the Bass, Treble and Balance slide potentiometers unplugs from the main board so it is easy to desolder the pots.

Here are the slide potentiometers and the replacement parts lined up for assembly.

The three black plastic pieces in the middle are the new contact bridges.

The replacement parts are just the plastic bridges. You must reuse the original contact components.
Here are the ones from this Beomaster installed in the bridges and then assembled into the slide potentiometers.

The bridges are not physically keyed so you could accidentally install them the wrong way. Make sure the bare contacts line up with the metal tracks. It is also important during the handling of the contacts to avoid disturbing the contact with the small, black coal piece.

Once the slide potentiometers are re-assembled their mounting holes to the board are keyed so the only thing to be careful with is that the 50KΩ potentiometer is placed in the Bass mounting location.

The rest of the task is just to snap and solder the potentiometers back into position on the removable board and remount it to the main board.

That is followed by a quick test play to make sure the reworked sliders function properly.

Note that I have the smoked glass display cover removed for polishing.

Beomaster 1900 (Type 2903): Replacing The Bass, Treble and Balance Slider Potentiometers

Now that the Beomaster can power back up I performed the 15 volt supply check and adjusted the No-Signal Current setting for the left and right channels.

Since the left and right channel No-Load Current adjustment went smoothly I expected the Beomaster to be able to finally play music again. I used an ipod Nano as the source to the Beomaster Tape input and a pair of Beovox S55 speakers for the outputs. To my surprise I had no sound in the left channel. After some quick debugging I found that the Nano source signals were present in the Beomaster up to the balance slider. It is common for the bass, treble and balance slider potentiometers to develop problems in these receivers.

Checking the balance slider I found that it was the culprit.

Note: The tabs shown by the red arrows below have to be bent straight in order to disassembly the potentiometer.

I thought about doing a creative repair with some glue but figured there must be a better solution.
As it turns out, Martin at Beoworld makes a replacement part for the black slider housing that moves to change the output. That black slider housing is the piece with the broken tabs the potentiometer contacts are secured with. I ordered a set of three replacement parts as all three slider potentiometers (bass, treble and balance) have a broken contact mounting tab.

Since it will take at least a week for the parts to come from Denmark I wanted to keep going with the Beomaster restoration. I pulled the bass, treble and balance slider potentiometers from a Beomaster 2400. The Beomaster 2400 turned out to have nice, intact slider contact assemblies so they will do nicely and I have new assemblies on order. In the exchange of parts I will only take the contact assembly as the Beomaster 2400 Bass slider potentiometer is 20KΩ and the Beomaster 1900 Bass slider potentiometer is 50KΩ.

I cleaned the potentiometer contact strips and contacts with a fiberglass brush and some Deoxit Fader Lube.

With the Beomaster 1900 slider pots cleaned and rebuilt it was time to test the Beomaster 1900 for sound again.

Sly's voice came out beautifully on both Beovox S55 speakers. All of the slider potentiometers really needed that restoration.