[Coco] CoCo Disk System Power Supply Issue...

[Gene Heskett]

On Saturday 09 May 2015 12:56:34 Steve Batson wrote:
> Working on a Floppy Drive my Cousin gave me...
>
> It's a Tandy 26-3131 Floppy Drive system with the short FD-501
> controller. I get now power out of the transformer. I removed the
> transformer from the supply, ohm'd out the primary and I have
> continuity there. The secondary has 2 red and two orange. I have
> continuity between the two orange and two red, but not between orange
> and red (possibly an open circuit here). I do not read a short between
> primary and secondary. So worst case, the transformer secondary is
> bad. I don't have a schematic of this thing which would be nice not
> only for testing, but also for replacement if necessary.
>
> Suggestions?

Lets apply some more logic here, Steve.

1. you need both 5 and 12 volts, and both need to be reasonably well 
regulated.

2. Apparently this transformer has a separate winding for each supply 
voltage.  Reason?  If it was a tapped winding, economy demands only 3 
wires.  You have 4.

3. So next is to power it up and measure the AC voltage of each pair.  I 
am guessing that one pair, probably the red pair, will measure out to 
about 6 to 8 volts AC.  The other, orange pair, probably in the 13 to 15 
volt range.  That voltage. rectified in a full wave bridge, will give a 
dc voltage in the filter capacitor of 8 to 9 volts which will regulate 
nicely to the 5 volts the drives logic needs, and the orange wires, 
after a fullwave bridge, will be 17 or so, that will regulate nicely to 
about 12 volts for the drives motors.

But first, what AC voltages are you measuring, on which color pair of 
wires?

Are the regulators stone cold, while the capactors show a good DC charge?

Cheers, Gene Heskett
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