Edition 54
Technical Trends - Urgent Repair
by Bryant Underwood, Public Safety Sourcing, Cassidian Communications

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There are times when Reverse Logistics and repair is more about luck and creativity than moving truckloads of product to a depot or forward stocking location. There are cases where the only solution is to repair the current system, whatever that takes. When these events occur, they tend to be stressful, difficult and often very frustrating. Lives and property are usually at stake. However, the pressure to be instantly creative presents tremendous rewards in personal satisfaction. I have had quite of few urgent repair requests, most of the time with no warning or pre-planning at all. Since these are not typical for most of you, I thought you would enjoy hearing how a couple of these were accomplished.

While at home over a Memorial Day Holiday I received a panicked call from an Assistant Warden at a nearby state prison facility with a power supply problem at a guard pod. Turns out there are regulations mandating that inmate cells open automatically in case of power loss or other emergencies. To meet these requirements prisons are often designed with pods of cells for the inmates that surround an elevated guard station. In this guard station all of the cells locks are remotely managed.

This arrangement saves on labor and reduces the risk of injury from inmate interaction. The downside is that if there is no power, the locks do not stay locked… making the loss of a power-supply one very bad situation. I grabbed up some test equipment and hurried over to the prison. When I got there the scene was pretty hectic. They had called in a bunch of staff to manually manage the pods and open/close the locks using keys. I pulled some covers from the control consoles and found a bad switchmode power supply. It was rated for 30 amps at 24v. I first attempted to repair the supply but no luck. The failure was in the flyback transformer and that part was encapsulated and not removable. By happenstance I had two wheelchair battery chargers at my home. Together they had enough current capacity to meet the system needs. Using a battery charger as a power supply is not just plug-and-play. I had to bypass the current sense and overcharge circuitry to get the full power out. I then paralleled these into the console with some temporary wiring connections and got them up and running through the holiday without incident. The overtime staff guards got to finish their holiday and by that Tuesday afternoon we had a replacement power supply installed and everything back to normal.

Late at night there was a fire at our local police department. Much of the communications systems were destroyed. With the spares we had on-hand and some repair we had the system back up and running before noon the next day except for the paging encoder. The irony was that the paging encoder was used to dispatch the fire department and until it was fixed there was no way to have fire service coverage for the city. The major damage was from heat on a nylon switch assembly. If I could just repair the nylon sleeve that held the switch contacts we would be good to go. If you have ever tied glue nylon you know how tough that can be. The solution is what is called flame-etching. If you have nylon and other polyamide plastics, they can be etched to accept adhesives producing a very strong bond. The trick is to expose the plastic to heat from a propane torch. I know what you are thinking-more heat, I thought the part was already melted. Yes, but not the right kind of heat. The heat from propane allows the propane gas to react with the plastic and build a layer where oxygen is bonded to the nylon surface. This etched layer will then accept several types of glue, especially CA type glues with a primer. OK, now for the real trick, what primer did I use? Baking soda. The hardening reaction in CA glues is based on PH. By flame-etching the surface and then priming with thin coating of baking soda, I got the part glued back together and the encoder worked great until we got a replacement shipped in.

So in addition to duct-tape and your Swiss Army Knife, don’t forget the propane torch, baking soda and super glue. Lastly for skills training consider watching old Macgyver episodes on your iPhone.
Bryant Underwood manages Public Safety Sourcing for Cassidian Communications, an EADS North America Company in Frisco Texas.

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