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Tuesday, April 24, 2018

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.

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