I worked on the Beomaster 8000 microcomputer board today. This Beomaster is an earlier model and uses a first-generation microcomputer board, unlike later models with directly replaceable, yet distinct, boards. I’ll show an example of a later model board at the end.
One issue with the first-generation boards is the metal enclosure surrounding the processor ICs. While necessary for shielding, it makes accessing components difficult. B&O used soldered metal tabs to connect the upper and lower sections, but these tabs are soldered to the board’s ground plane, requiring significant heat for removal. This often leads to damaged traces, a problem evident in this Beomaster.
The picture below shows both microcomputer board types. The project board is at the bottom. Note the press-to-fit shield box on the top board versus the soldered one on the bottom (red circles indicate solder points).
This is the project’s microcomputer board before restoration:
And here are the covers removed:
Early models used a metal bar heatsink on the main processor ICs (IC3 & IC4). The red circles highlight damage where the case mounting tabs were. The previous repair soldered the box shut, but I’ll avoid this due to grounding concerns.
Similar to Beogram 8000 & 8002 turntables, special tape isolates thermal paste from ICs. Here’s the component side with tape removed. Restoration includes replacing the 22uF electrolytic capacitor with a 105°C high-reliability type, replacing the 1uF tantalum capacitor, and following Beolover’s guidance, replacing oscillators X1 & X2, requiring new matching capacitors (18pF). Finally, I’ll reflow solder joints on connectors and vias to address potential hidden problems.
This board has two 12pF capacitors per oscillator. One has them on the component side, the other on the trace side.
Later models have component-side mounting holes for these capacitors.
Here’s the board with updated components. Caution: As Beolover noted, modifying crystal oscillators risks damaging processor ICs (IC3 & IC4). I shorted oscillator leads and removed these ICs (with ESD protection) before working on the board.
After reflowing, I reinstalled IC3 and IC4, then prepared the heatsink, applying thermal tape and compound before reattaching the covers.
To fix the broken ground points, I used copper tape like metal bands on shipping crates. I soldered these bands together above and below the box, then soldered them to the box for proper grounding. To connect the box to the board’s ground planes, I ran copper tape straps to the main ground lug on both sides.
The result isn’t pretty, but it’s sturdy and functional. The straps secure the box, and ground continuity is excellent. Next time, I’ll apply copper strips to the lid pieces as solder anchors before attaching the bands.
Removing the assembly is straightforward. By not soldering the side straps, I can open the box by cutting them, desoldering the two main ground straps, and lifting it open. Red arrows in the image indicate cut points. Green arrows show a previous repair where a ground connection was established by soldering to the scraped board coating, which I find risky due to potential cracking. I prefer straps for a more reliable, flexible connection.
Testing the updated board in the Beomaster 8000 was a success. It’s now undergoing a thorough test run to ensure no further issues arise.
For reference: A later model Beomaster 8000 microcomputer board, restored previously.
These cover plates are easy to remove, as they’re press-to-fit. The rectangular tabs on the top plate contact processor ICs (IC3 & IC4) to dissipate heat through the metal shield box.
Here’s the restored component side. Both 18pF capacitor sets for the new oscillators are on this side. Note the permanently mounted frame for the covers, providing structure without stressing the board or requiring soldering. Much better for servicing.
The trace side required only solder reflow.
Now, back to assembling the Beomaster 8000 display modules to finalize the last board.