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Thursday, November 16, 2017

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.

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