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.

Beomaster 8000: Replacing The Microcomputer 2MHz Oscillator Crystals

A while back Beolover encountered a fault where a 2MHz Oscillator Crystal failed in his Beomaster 8000 receiver. Needless to say the Beomaster did not operate properly. You can read about the failure in his previous blog post here.

Since that time we have been replacing these oscillators on our Beomaster 8000 restorations as a preventative measure. The Beomaster 8000 is rather expensive to ship so it is a good idea to guard against faults we have seen before.

As Beolover warns in the original post, you have to take some care and precautions when changing the two oscillator crystals (one for each microcomputer IC). The microcomputer devices can no longer be sourced if a replacement is needed except to raid another Beomaster 8000 unit.

To get started I removed the microcomputer board from the Beomaster again and removed the original oscillator devices.

This picture shows the precaution I use where I short the oscillator pins when the device is desoldered for removal. I also keep the oscillator leads shorted during installation. Shorting the oscillator leads will insure no electrical discharge from the devices cause (fatal) damage to the microcomputer chips.

ADDITIONAL NOTE: Along with shorting the two oscillator device leads together during the removal and installation - the leads should also be connected to the the board ground....which should be connected to the ground of your ESD protective band. Anytime you are handling integrated circuits on these boards you should wear ESD protective bands and properly ground them.

Along with the X1 and X2 oscillator devices capacitors C17, C18, C95 and C97 capacitors must be changed. The capacitor values are determined by the oscillator device.  In this case I used the same oscillator that Beolover originally used (21M6819). That oscillator calls for two 18pF capacitors.

Here are the new parts installed on the microcomputer board. I used a little Aleene's Tacky Glue to secure the oscillators to the board.

After re-installing the microcomputer board back in the Beomaster I started up the receiver and I am now listening to the FM tuner again. Another task off the list.

The display board is next on the list.

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.