Technical Note 219

TN 219 Arm Position Contact Cleaning


Some DeNovix products include a patented mechanism for detecting that the arm has been lowered to the “down” or “closed” position. On rare occasions, a resistive layer can build up and need to be removed.  The contact button in the arm and the screw head will need to be cleaned and then roughened/sanded to remove the resistive layer so the mechanism can function properly. This technical note describes the steps for refurbishing these components and restoring proper function.

Arm Contact and Screw

Normally when the arm is down, an electrical circuit is completed between the contact button (Figure 1 – ) in the arm and  the head of the screw (Figure 1 – ② ). The instrument reliably detects this contact. However if there is contamination or an oxidized layer interfering with the two contact points, a “Lower Arm” alert may be present even when the arm is in the down position. Ethanol cleaning followed by a buffing/sanding of the components will remove the resistive layer. Follow both steps below.

Figure 1.

Step 1. Ethanol Cleaning of Contact Points

  1. Spray a standard laboratory wipe with 70% ethanol. Do not pour or douse the instrument directly with the fluid.
  2. Lift the instrument arm.
  3. Using the lab wipe, vigorously clean the contact button located on the bottom of the arm (Figure 2).
  4. Repeat this process and clean the top of the screw. (Figure 3).
Figure 2.
Figure 3.

Step 2. Sand / Scrape the Arm Contact Button and Screw

This step requires use of a material capable of sanding or abrading a surface. Use emery cloth, fine grit sandpaper or a similar material. Alternates that can remove a contaminant or oxidized layer include items such as the edge of a coin, X-ACTO knife blade, steel wool, etc.

  1. Lift the instrument arm.
  2. Using the emery cloth, buff/sand the contact button located on the bottom of the arm (Figure 4).
  3. Repeat this process and buff / sand the top of the screw. (Figure 5).
  4. Spray a lab wipe with 70% ethanol.
  5. Use the wipe to clean the contact button and the arm screw to ensure all debris from the buffing operation has been removed.
  6. Lower arm to check if the contact is now correctly detected. Power cycling the instrument may be required.
  7. If the arm is down and an alert is still present, contact DeNovix or your local Distributor for further assistance.
Figure 4.
Figure 5.

Revised 03 Sept 2021