[Coco] fuzzy deuce?

RJRTTY at aol.com RJRTTY at aol.com
Thu Apr 15 23:34:05 EDT 2004


     During work on my repack I found out why the RF out on the coco3 is
generally cleaner  than a coco1 or 2.  At first I powered the main board by
putting 24 V DC across the main diode bridge at the point where the
AC transformer was connected.  Everything seemed to work fine
until I noticed I had no sound and no RF output.  It turns out that a
a seperate power connection on the ac side of the bridge was connected
via an electrolytic capacitor to a seperate pair of diodes which
then connected to an independent voltage regulater outputing 8 Volts.
The sound interface and RF modulator both use this
independent voltage source to avoid the noise on the main supply.
Just when you think tandy suffered from a lack of comittment when it
came to certain aspects in the design of the coco3, you find something
like this.  It works so well that I am going to duplicate the circuit on a
seperate board outputing buffered sound and video for some of my
coco 1 and 2's.
    The solution I used to complete my repack was to use the orginal
transformer and its shielding cover to power the main board and let
the repacks main power supply supply the multi pak interface board
and floppy drives.  Every thing works well.


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