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Sunday, May 6, 2018

Beomaster 8000: Reassembly for Testing

I can finally start putting this Beomaster back together where it can be put through some functional tests. There is a final component that needs attending to however and that is the door damper for the lid that covers the Filter & Tone Control panel.

The Beomaster 6000, 8000 and Beocord units from this period share a door damper component that keeps a spring loaded lid from flying open. The damper applies some resistance to the spring so the door opening is more controlled.

Here is the damper that came out of this Beomaster 8000 unit. You can see that damping grease has started to leak out. I have seen units where the damping devices are still sealed and don't leak but I have also seen a bunch that are leaking. My guess that the environment they were stored in plays a part in how they have survived.

Here is the damping component opened up.

Ready for the new damping grease.

Here is the reassembled damper installed back in its place in the Beomaster.

It is easiest to reattach the door to the damping component with the Filter & Tone Control board removed. Now that the door is working again I can continue with the rest of the Beomaster reassembly.

During this phase of the project I test play the Beomaster every chance I get. The more actual use of the restored receiver the better. I noticed that the FM tuner didn't sound right and looking at the Signal-Multipath meter in the photo above there should be an illuminated red "MPX" lit up. It is dark in the photo. When the Beomaster 8000 is tuned to an FM stereo station the MPX lamp lights up to indicate it is decoding stereo FM. That is what my ears were trying to tell me. The FM tuner was tuning stations but they were only playing mono.

That means lifting the Filter & Tone Control panel to do a little trouble-shooting of the FM board. Since the problem seemed to involve just the FM stereo functionality I concentrated on the things that just relate to that.

I made some minor adjustments to the 1R45 (Stereo Decoder - oscillator) and 1R41 (Opening of Stereo Decoder) trimmer resistors. Doing that got the MPX LEDs in the Signal-Multipath meter to illuminate on an FM stereo channel. Unfortunately I was still only hearing mono from the Beomaster.

That left the Stereo Decoder chip (1IC3) as the next suspect. It is responsible for decoding the stereo signal.  Fortunately I had a spare TCA 4500A chip in stock.

That did the trick. The FM stereo channels now decode properly and the tuner sounds good again.
Here is the fixed FM tuner. The red arrow points out the illuminating MPX light.

Now to finish closing this unit up and begin the final testing.

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