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Thursday, February 1, 2018

Beomaster 8000: Microcomputer Board

Time for the Beomaster 8000 microcomputer board work.
Here is the board removed from the Beomaster.

The components I am interested in are inside the metal shielding box. This board has improved for the better from earlier serial number Beomaster 8000 units. The original metal boxes were soldered shut and a real pain to open up. It was very easy for the circuit board to get damaged when de-soldering and opening up the box. I have seen several units with copper pads torn from the board. This newer shield box has snap on lids for the top and bottom sides. Very easy and much appreciated.

There are just two capacitors that will be replaced as part of the Beomaster recapping effort. A 1uF tantalum and a 22uF electrolytic. You can see on the 22uF electrolytic and some other nearby components that this board has some solder point vias where both the underside (trace side) and component side must be soldered.

Part of this restoration is to reflow solder for the vias and board connectors.

Another update on this microcomputer board will be to change out the crystal oscillators for the two processor chips. The reason for this is that we have seen some cases where those components begin to fail so we go ahead and change them now. Here is a previous Beolover Beomaster 8000 restoration where we first encountered problems with the oscillators. Better to be safe than sorry.

Changing the crystal oscillators means changing four ceramic capacitors (two for each oscillator). The capacitance of those capacitors is defined by the crystal oscillator device. The new replacement 2MHz oscillators call for two 18pF capacitors so that is what I am using.

This picture shows the original oscillator components that will be replaced. Per the information on the earlier Beolover post I shorted the oscillator leads and removed the two microcomputer ICs (wearing proper anti-static protection of course).  Having the microcomputer ICs out of the way is a safety step to avoid any damage to the chips.

And here are the replaced components. The new crystal oscillators are much smaller. The original components were secured by some double-sided tape. I removed the old tape and used some Aleene's Tacky Glue.

Here is the completed microcomputer board before putting the shield box lids back on.
Note that the oscillator leads were again shorted together for the reinstallation of the microcomputer chips in their sockets.

Now it is on to the Beomaster 8000 display board.

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