Any customer that has a Bennett or HCMI high frequency generator has seen the infamous HYFOB error more than once. Of course we all know that HYFOB is an acronym for Hold Your Finger on Button and the generator displays the error if the customer lifts their finger off the prep or expose button before the end of the exposure. This is a nice friendly reminder to the operator but who would have guessed that the prep & expose buttons would be the highest failed component in the whole generator. When the buttons begin to wear out and fail to make good contact, it simulates a HYFOB error even though the operator never lifted their finger off the buttons. The fix to this is to replace the operator console membrane at a cost of close to $1,000 to the customer . . . OUCH! After getting more and more of these complaints from customers we decided to see if we could come up with a less expensive fix. What we came up with was a prep / expose switch box out boarded from the operator console. We purchased a set of momentary switches and a nice box with precut holes and a 6’ length of 2 pair cable. The switches are wired so that both have to be depressed in order to complete the exposure circuit path and lifting either prematurely would simulate the HYFOB. The cable leads are then soldered to the prep and expose points on the console control circuit board. We even found a replacement terminal connector that will solder directly to the board and the wires can be attached with screw terminals for easy removal if need be. You can build one of these boxes yourself or you can purchase one from Z&Z Medical, item #XSWT1 for $150, assembled with installation instructions. The end result is a very inexpensive fix compared to replacing the entire control pad. Here is a brief description and pictures describing how to install this outboard switch box from our technician/developer, Kevin Geerts.
I used a standard 22mm two hole box, industrial start/ stop normally open momentary switches with two separate colors. These are available online. I purchased mine from Automation, part numbers Box = SA106-40SL deep two hole box. Prep switch = GCX1102 and Expose switch = GCX1103 . I wired the switches with approximately 6’ of four conductor wire (for trouble shooting purposes). You could use three conductor and tie the commons together in the box but I prefer to leave them separate. I used the yellow switch for prep and green for expose.
Power down the machine and remove power from generator entirely to prevent accidental power up and possible exposure. The console pictured is one of two possible consoles you will find in use. This one is a large style console, not as common as the smaller style but the following steps apply to all.
Remove the console cover and locate the main control card. Locate the Prep/Expose through hole terminals.
Remove the control card from console taking care to note all connections and wiring for replacement later. Use ESD precautions as chips on this card are susceptible to damage from ESD discharge. Remove the solder from the Prep, Expose and Common through hole connections. Attach and then solder your attachment points. Used here is a standard three hole screw type terminal strip. Other connections are possible but this is one that I scavenged from another project board.
Remount the control card in the console and reattach all existing cables. Route new Prep/ Expose switch assembly wires and secure them with tie wraps to the console case to prevent pullout. The large consoles have cable access holes that work to bring the cable in. Smaller consoles may require the installer to drill a small hole through the metal backplane (near the on/off switch) to run the new cable through.
Attach new Prep/Expose Switch wires to connector/s previously added, Prep to Prep, Expose to Expose and the commons together on the common. Finish the reassembly and closure of console rechecking for loose connections. (these can be a plague of headaches if you don’t). Level and mount the new Prep/Expose switch box in customer preferred location.
Test your work taking long and short shots to determine if your HYFOB’s have been cured.