Dataman S4/S4 Validator Contrast Wheel Replacement

• Working on a non-metallic surface, remove the back cover of S4, which is held by 4 small screws, and ease the case apart. The back cover contains the battery and the sounder and is connected to the PCB by two cables. It is not necessary to disconnect these, but note that S4's on/off switch doesn't interrupt the battery supply - the electronics is still powered - and a NiCd can deliver an impressively destructive current.
• When you open the case the broken knob will fall out, but its center pin remains in the pot. Unfortunately it is tapered, and you cannot push it out from the rear. You will need to remove the main PCB. This is located by case pillars and has two rows of connector pins - one attached to the display, the other to the keyboard. The pins are slender and fairly fragile if bent. It is easier to release the PCB from the keyboard first by gently levering the board against the case top; then release it from the display in the same fashion. The button on the on/off switch will fall off, by the way, as the case holds it in place.
• You can now push the broken pin out of the pot through a hole in the PCB, using a bent paper clip, and insert the new one. The pin is hexagonal, with six possible orientations - if you rotate the pot fully CCW, the projection on the knob should be towards the on/off switch and fully inboard.
• Assembly is the reverse of disassembly. When you replace the main PCB, use the molded case lugs as location guides and line up the keyboard first. It is quite a tight fit, and you will have to press quite hard. Remember to replace the on/off switch knob before you seat the board, as you cannot afterwards. When you replace the back, don't trap the wires under the battery, as there's a temperature sensor on the PCB.

If you should break anything, don't worry - we can repair the unit here and your warranty is not affected.