Autostar Keypad Contact Repair
By K.C. Kile, Sr.
At some point in the life of your Autostar handset, it’s response to your input will most likely become less than desired. This may happen at the beginning when the unit is new, or appear after several years of use. The first instinct is to open the handset and clean the pads and contacts with alcohol. This is a definite NO-NO. Although your cotton swab will become black with material that you attribute to the problem, performance of the handset will be further degraded, as you have just removed the substance apparently used to insure good contact. I have found the most effective repair to be obtained from the Chemtronics CW2605 Rubber Keypad Repair Kit shown in Figure 1. This kit can generally be purchased from major electronic parts supply stores for under $15 and is of sufficient quantity to do approximately 20 handsets. The down side is that it only has a 72 hour pot life after mixing. DO NOT attempt partial product mixing to conserve!
Start by placing the handset face down and removing the 4 screws arrowed in Figure 2.
This now allows removal of the back portion of the handset as shown in Figure 3. Remember to observe antistatic precautions from this point forward to protect the IC’s.
Pay close attention when separating the two halves as the red filter for the handset lamp, shown to the right in Figure 4, is not permanently attached and is now free to be dropped, lost, stepped on, or otherwise broken.
In addition, although the white display background block arrowed in Figure 5 uses double sided tape to retain it to the rear portion of the handset housing, this sometimes does not hold and allows the block to become free to move.
Figure 6 shows the display background block removed on this particular handset.
Next will be the removal of the display ribbon cable from its contact holder on the circuit board. This is accomplished by individually moving the edges of the contact holder nearest the ribbon cable, arrowed in Figure 7. Simultaneous movement of both edges generally results in separation of the moving part from the soldered base, and risks potential breakage of an end tang or other damage which can be difficult to repair. Continue to Figure 8 for clarification.
Again; individually move the edges of the contact holder toward the display approximately 1/16 inch as shown in Figure 8. The ribbon cable can now be pulled from the contact holder, allowing the circuit board to be removed and free of attachments.
Figure 9 displays the removed circuit board displaying its contact side, and the exposed keypad contacts in the front handset housing.
Remove the keypad from the front housing and clean all contacts on both the keypad and circuit board with the supplied cotton swab and clear 91% isopropyl alcohol until no residue appears on the cotton. This is especially important for the rubber keypad contacts in order to obtain a good and lasting bond of the repair material. Allow at least an hour drying time for the keypad before attempting the repair. Some of this time can be spent preparing the repair material as the packaging, storage, and display methods of the kit require diligence in its preparation. Figure 10 shows a considerable amount of the silver impregnated compound adhering to the lid and sides of the container.
Using something such as a 6 inch metal pocket ruler scrape the lid and sides free of the misplaced compound for return to the bottom of the container as shown in Figure 11.
After retrieving as much as possible, pour in fully the small amount of fixer from the supply bottle and mix thoroughly for a minimum of 1 minute using the included plastic stirring rod seen in Figure 12.
Now dip the bristles of the kit’s brush no more than 1/3 of the way into the mixture and use it to apply a VERY THIN LAYER onto each of the keyboard contact TIPS as in Figure 13. Start by daubing the tip center, and then use multiple strokes to achieve full tip coverage. Light brush marks will shrink on drying. DO NOT attempt to clean mishaps that will occur, especially in the small rectangle areas, until product dries after 24 hours!
As can be seen in Figure 14, on completion of product application there has been some degree of sloppiness involved with the brush and mixture in tight areas. After 24 hours, these areas will become hard and can be carefully scrapped off with a hobby knife. Use the back side tip of the blade as much as possible to avoid cutting or tearing of the thin keypad rubber. The handset can now be reassembled. Don’t forget to lock the ribbon cable back in its connector.