22 Aug
2015
22 Aug
'15
4:06 p.m.
On 8/22/2015 2:41 PM, Jay Jaeger wrote:
Unfortunately, bearings did not help the floppy drive, so now I am busy
taking the floppy power supply I got with my FD 100-8, making sure it is
up to spec to use with the Shugart (and correcting that if needs be),
and making it safer (mains fuse, switch) and more fault tolerant (fuse
in the 24V line, at least) and making sure all of the mains connected
innards are not exposed. Just about done with that. The +24V and -7 to
-16V are in spec, but the +5V (which, curiously for a 1A supply, does
NOT use a simple 3 terminal regulator) is a tad high, at 5.35V. I may
just change it to use a three terminal unit.
Well, just found another reversed electrolytic - but this time the
original fault was not my own. I decided to trace out this floppy
supply I have had for decades (back in my original Altair days), that I
got from the same guy from whom I purchased my Siemens FDD 100-8, and
discovered that the electrolytic on the unregulated -7 to -16 V was
reversed - installed BACKWARDS. That capacitor is now in "reform
school". ;)
Also, I now know why the +5 V is high. It has a UA 7805 3 terminal
regulator serving as a voltage reference for a TIP-3055 so the supply
can provide more current. That 7805 has a forward biased diode between
the center terminal and ground, thus raising the output voltage by right
around 0.5v. I expect I will leave it alone.
The same design is used for the +24V, which comes out at 24.2V.
So, odds are that this supply could drive two floppy drives.
JRJ
JRJ