3.6.6 Stacy PSU

STACY PSU: Drive's +5V Rail Upgrade

Here is a solution, ending my miserable hard drive/power supply problems for my STacy. Have you wanted to replace your inadequate stock CONNER hard drive with a larger model?

You may have found that there isn't enough power available from the stock power supply, and with goodies like GCR, the entire computer crashes and reboots.

WHY??

The stock PHIHONG power supply's specifications are: 16.5V at 2.5 amps. I found by watching the oscilloscope during floppy and hard drive accesses that the external power supply can deliver EXACTLY 2.5 AMPS and NO MORE! If the load exceeds 2.500000 amps, it shuts down until the load has returned to under 2.5 amps.

Nothing seemed to help. I tried tweaking the 12 and 5V potentiometers on the internal power supply board, trying other hard drives, large filter capacitors on the 5 and 12 volt lines and trying non-ATARI floppy drives. No luck here....

THE SOLUTION.......was finally discovered when I realized that by improving the filtering and stability of the power supply, the transient current loads no longer exceeded the maximum supply ratings. Simply, de-solder the 5v line leading to the hard drive at the power/regulation board. Solder the input leg of a LM340K-5 (5v, 3amp positive-voltage regulator) to the 12v line. Solder the case (GND) to the GND terminals between the 12 and 5v lines on the power supply/regulation board. Solder the wire leading to the hard drive 5volt line to the output leg of the LM340K-5. This solution has been flawless, running an impressive 2 years now!

---------------
         (5v)  |
             O |               _________________> 5v to hard drive internal
               |              |
power supply   |              |
and regulation |              |  output (5v) board
               |              \   _______________
               |               \__|             |
               |   (gnd)          |             |
       (gnd) O--------------------|  LM340K-5   |    (5v, 3A voltage
             O |                __|             |     regulator)
               |               /  |             |
               |    __________/   ---------------
               |    |            input  (12v)
               |    |
          (12v)|    |
             O |---------------------------------> 12v to hard drive
---------------

A am not responsible for your results or screw-ups. Try it at your own risk, of course. Phil McCandless