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Thursday, October 18, 2018

Canada Beomaster 8000: Microcomputer Board Completed

I completed the electrolytic capacitor replacement on the Beomaster 8000 a few posts back. When I changed the two capacitors on the microcomputer and display boards I said I would return to the two boards later to finish their restoration tasks. I did that because I wanted to test the Beomaster power supply voltages first. Now that the power supply tests are out of the way I returned to the microcomputer board and completed the last task there.

The final microcomputer board task was to replace the two 2 MHz crystal oscillators with new ones. We like to replace the two oscillator devices because the Beomaster 8000 is such a heavy and expensive component to ship. Beolover first ran into a problem with the Beomaster 8000 2 MHz oscillator devices in a 2016 restoration. Since then we decided to make that replacement on all of our Beomaster 8000 restorations that involve shipping. Think of it as insurance.

The replacement is not terribly difficult but care must be taken to not damage the two microcomputer board processor devices.

Here is the board as I left it after the recap. The crystal oscillators and their related capacitors are highlighted.

This is a closer look at the 2 MHz oscillator devices and their 12pF ceramic capacitors.

Before de-soldering and removing the existing 2 MHz oscillator devices the leads are shorted and the two processor devices (9IC3 & 9IC4) are removed. The red alligator clip connects the board ground to my shop power ground and my electrostatic discharge wristband. It is important to protect against static discharge when working with integrated circuits. Especially when some of these integrated circuits are not available anymore.

This picture shows the oscillators removed.

The new crystal oscillator devices are 2 MHz oscillators but their spec sheet specifies that they require 18pF capacitors instead of the 12pF capacitors the old oscillator devices required.

The metal lids are then reattached to the microcomputer board shield box and I tested that the Beomaster microcomputer board still works.

The control panel still functions so the microcomputer board looks like it is ready to go.

The display has some failed segments. To verify that I will remove the four segmented display modules and see how they do on the test jig.

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