In order to troubleshoot touchpad problems, it is important to understand the interaction between the touchpad and the controller.

The control board communicates with the touchpad using both direct control signals and a serial IIC interface (also called I2 C or I2C). The direct control signals come from the ON and OFF buttons on the touchpad. These signals directly activate or deactivate the relay, K1, which, in turn, activates or deactivates the Master Power relay on the Opto22 board that supplies power to all the valves. The microcontroller monitors the state of this relay to determine if the sterilizer is ON or OFF. In the OFF state, the microprocessor shuts off all outputs, shuts down jacket control, and turns off the touchpad LEDs and display. However, the microprocessor is still running in the background and monitoring the relay K1. When the ON button is pressed, relay K1 switches states, which triggers the microprocessor to again turn on the touchpad LEDs and display.


Dark Bars on Display

On double-door units, both touchpads are connected in parallel and each touchpad is addressed through the I2C protocol. A jumper on the touchpad is used to set an address bit to distinguish between Side A and Side B. When the jumper is ON, the touchpad responds as Side A; OFF for Side B. For sterilizers with a single door, if the jumper is removed the display will appear as dark bars and only the ON / OFF buttons will not respond.

Touchpad displays are equipped with a contrast adjustment. Turning the adjustment potentiometer too far in one direction can cause some displays to show only dark bars. Turning it too far in the opposite direction can cause the display to appear blank.

Blank Display

At power-up, the microcontroller must initialize the LCD on the touchpad using the I2C interface. Power-up is the only time this happens. If the initialization does not occur for some reason, such as the cable not being connected, the light on the LCD will illuminate, but it will not display messages. In some cases, if initialization does not occur, the LCD may display its own message of “Uninit.” In either case, the solution is to ensure that the touchpad is properly connected and then cycle power on the control box.

The touchpad connector must be in the correct orientation in order for the touchpad and controller to communicate. The photos below show the proper orientation for touchpad cables on the control board. Horizontal touchpads use a 10-conductor ribbon cable. The red wire on the cable indicates Pin 1. Vertical touchpads use a 10-conductor round cable. The red wire on the cable is also positioned at Pin 1. If a cable is unplugged while the control board is powered, re-plugging will activate the backlight but not the display. Pressing OFF and then ON will re-activate the display.

In some cases, a blank screen can be caused by poor pressure calibration. In normal operation, if the controller detects a chamber pressure of greater than 40 PSIG or less than 40 InHg at power-up, the display backlight will light but nothing will be displayed. This can be checked by turning off the power, switching to CAL mode, and then turning the power back on. If the display becomes active, navigate to the SENSOR DIAGS and then to Chamber Pressure to check the perceived pressure. If the perceived pressure is outside the limits, pressure calibration or pressure sensor replacement may be necessary to fix the problem.

ON-OFF Button Problems

Since the ON and OFF buttons are a direct connection while the other buttons and LEDs are controlled via a serial interface, it is possible that a display can work correctly in all other functions, but have problems turning the sterilizer on or off. If this problem occurs, a step-by-step methodology should be used to isolate the problem.

1) To determine if the problem is in the touchpad, bypass the button and short across the button terminals on the back side. With the control box breaker switch in the ON position, shorting the brown and white terminals should turn the unit ON. Shorting the green and white terminals should turn the unit OFF. If this procedure works, the problem is likely the touchpad. If not, try the next step.

2) To determine if the problem is in the cable, try shorting across the Pins of J3 which should switch the board relay ON and OFF. With the control box breaker switch in the ON position, unplug the touchpad cable from J3 on the control board. Temporarily remove the shorting block from the MP jumper and use it to short across Pins 7 & 8 to switch the relay to the ON position (see photo on next page). Short across Pins 9 & 10 to move the relay to the OFF position. As each set of pins is shorted, a click should be heard as the relay switches positions. Additionally, an ohm meter across the contacts of J2 can be used to determine that the relay is turning OFF and ON when the pins are shorted. The contacts should be open when in the OFF position and shorted when in the ON position. If this procedure works and shorting across the touchpad terminals in Step 1 did not work, the problem is in the cable.

Be Sure to Replace the Shorting Block on the MPJumper

The relay will remain in its last position even when power is removed.
Therefore, switching the relay to the ON position, then replacing the touchpad
cable and cycling power, can be a temporary fix to turn on a sterilizer whose
touchpad functions properly except for the ON / OFF switch.

3) If the shorting procedure in Step 2 does not cause the relay to switch positions, this may be a sign of a bad relay or some other control board problem. On rare occasions, the relay may have become stuck. Try gently tapping on the relay (K1 in the photo above) with the handle of a screwdriver and then repeating Step 2. If this does not fix the problem, the control board will need to be replaced.

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at dschall@spire-is.com.

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