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

[Steve Batson]

Thanks Gene...

I did come to the conclusion about the Transformer while I was thinking about it before your message. In any case, I disassembled the unit more so I could see and inspect everything. All transformer voltages were good. No fried components, shorts or opens from what I could see. I did end up repairing a broken connection to the board from the transformer. All voltages were good, so I plugged it in and the drive is working, talking to the controller and I was able to access data on a floppy.
 
Now on to the rest of the stuff he gave me :)



On May 9, 2015, at 3:09 PM, Gene Heskett <gheskett at wdtv.com> wrote:

> 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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> 
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