Unidisk Write Protect Mod

This is Ed's Mod for Unidisk Drives to override the Write Protect.

The way the write protect sensor works on newer drives is that a LED on one side shines on a photoresistor (the sensor) on the other side. The light passes through when there is a notch and does not pass through when the notch is covered. When light passes through the write protect notch, the sensor which is normally open, closes and completes the write enable circuit.

What we will do is give the write enable circuit an alternate enable option using a switch. Pressing the button will complete the circuit and enable the drive to write on the disk.

Find a small momentary Normally open push-button switch. Use wire long enough to get from where you want to mount the switch over by CN1. I normally mount the switch on the front plate of the drive by drilling a tapered hole (using scissors) and screwing the threaded base of the switch into the hole with the button protruding on the outside. Then solder one wire from the switch to each of the sensor leads.

Once this modification is complete, simply holding the button will override the write protect. With a fast copy program I hold it for 30 seconds or so per disk. I like this because I never have to remember to flip the switch back for normal operation.

To override the write protect switch on a Unidisk

Disclaimer: Use at your own risk, I will not take responsibilty for you breaking your drives.

Click images for larger view.

1. Turn off the computer. Remove the drive from the computer.

2. Open the Unidisk by removing the two screws at the back. Lift up the top cover and slide rearwards to remove, gently sliding the cable down to free it.

3. Remove the screw on top holding the top RF shield (metal cover) and grounding strap. Pry the cover up near where the screw was and slide it forward a bit then lift up to remove. (Note the hooks at the front that hold it on.)

4. Near the front you will see a large connector labeled CN1. Pins 9 and 11 of CN1 are the write protect sensor. To override the sensor you can short those two pins together. This is effectively what our switch will do.

5. Decide where to mount your switch. I decided to mount the switch in the upper left part of the face plate, opposite the light to balance the look. Run to your junk drawer and find some appropriately size and length wire and properly sized switch. (Radio Shack is my favorite junk drawer.)

6. Drill the holes and make room as necessary for mounting the switch. A tapered hole will allow you to screw the switch into the hole so the threads can bite into the plastic and hold the switch in place without using the nut normally required. I had to carve a notch in the plasic to make room for the body of the switch behind the face plate.

In this picture note the hole in the face plate, the notch to make room for the switch behind the faceplate, and the switch itself, sitting on the drive above the hole. (I positioned the hole too close to the top and had a very difficult time screwing the switch into the faceplate.)

7. Solder the wires to the switch. Mount the switch in to the face plate. Run the wires over by CN1 making sure they will not interfere with the mechanical working of the drive. Test fit it all as you go.

Not being one who wants to mess up a perfectly good connector, we will use alternate points on the board to actually hook our momentary switch to. Those pins come out at R12 and J29 over by the CN1 connector.

6. Solder the wires from the momentary switch to the circuit board edge side of R12 and to the wire at J29.

So to override the write protect, simply hold the momentary switch while writing. Go ahead and plug it in and test it.

When you are satisfied it works, reassemble the drive.

Of course if you really want the protect/ normal/ enable modes, get a Single Pole, double throw, center off switch. Solder wires to the three leads and mount the switch. Cut the wire to pin 9 on CN1 (orange). Solder the connector end to the center wire of the switch, hook the other end of the wire from the sensor to one end wire from the switch. Hook the last switch wire to J29. (One last tip, sometimes the center wire is called 'common'.)

                         Switch
Orange wire from bundle ----O
     Orange wire to CN1 ----O
                    J29 ----O

This Page was Authored and is Copyrighted by Delfs

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