Check that power has been connected using a voltmeter on the CPU board to make sure that the correct voltage is present. If the voltage reads very low, the problem may be that a fail safe lock being controlled by the DK-26 is drawing too much current for the power supply. Remove the lock from the circuit. If this restores proper voltage and operation of the DK-26, you'll have to determine if the power supply is undersized or if there is a short circuit in the lock wiring which is pulling down the power supply. If the DK-26 is receiving specified voltage, briefly short terminal SRC to terminal REX. You should hear the relay click. This confirms that the CPU board is working but for some reason, it's not reading the keys. Make sure that the keypad cable is connected exactly as shown in instructions. Pay particular attention to the keypad white wire going into terminal WHT. If this wire is not connected, the keypad will appear to be dead. If the relay doesn't operate when SRC and REX are connected, the CPU board has either tripped one of its automatic fuses or has some major problem requiring replacement. The DK-26 employs three special type fuses called PolySwitches. PolySwitches look like capacitors. When a PolySwitch goes into overload, it automatically adds a high resistance to the circuit which limits current flow to about 100mA, protecting the circuit. Each PolySwitch protects against a particular problem and you need to know how to determine if the PolySwitch has tripped and how to correct the problem and reset the PolySwitch. PolySwitch #1 comes into play when you are powering the unit from an AC source connected to the AC input terminals. It protects against an internal short on the board. If you are powering the board with DC voltage into the DC input terminals, ignore PolySwitch #1.PolySwitch #2 protects against an internal DC short circuit on the CPU board. PolySwitch #3 protects against a short circuit in the keypad which can be caused by skinned keypad wires or mis-wiring the keypad cable into the CPU board terminals. PolySwitch #3 will also trip if there are short circuit problems with the SRC, REX, UCD and HCD terminals.To check the PolySwitches, apply the probes of a voltmeter to both PolySwitch leads with the board powered. If you are checking PolySwitch #1, set your voltmeter to AC. Set it to DC for PolySwitches #2 and #3. In the normal condition, the PolySwitch will be conducting current so you will read less than one volt. A tripped PolySwitch acts as a high impedance resistor so you will read several volts across the PolySwitch leads. If none of the three PolySwitches have tripped but the properly powered board will not operate its relay when SRC and REX are briefly shorted together, call the factory.If you find a tripped PolySwitch, you have reset it. Overload current through the PolySwitch trips it so that it clamps the current down to roughly 100mA. The PolySwitch will continue to clamp until all power is removed for about 5 seconds. It is not enough to correct the overload condition; you have to depower the board for 5 seconds and the PolySwitch will reset itself. If PolySwitch #1 has tripped, visually inspect the four large diodes on the board to see if a loose wire has fallen on them to create a short circuit. If you do not find such a physical problem that can be easily corrected, the board should be replaced although you should be aware that it can be operated with no problems from a DC power supply connected into the DC input terminals. If PolySwitch #2 has tripped, and you are using DC power, make sure your input polarity is correct. Reversing your input polarity will trip PolySwitch #2. Otherwise, look for any loose wires that could be creating a short circuit anywhere on the board. If you can't correct the fault that is tripping PolySwitch #2, the board must be replaced. If PolySwitch #3 has tripped, the overload condition is in the keypad wiring or in terminals SRC, REX, UCD and HCD. Carefully make sure that all keypad wires are connected to the correct terminals. If they are, temporarily disconnect the keypad and attempt to reset PolySwitch #3 by de-powering the board for 5 seconds. Once the board has been re-powered, momentarily connect SRC to REX to see if the board will function (the lock control relay will operate). If the CPU board resumes function, reconnect the keypad. If PolySwitch #3 trips again, the keypad will need to be replaced. If the CPU board did not resume function, disconnect any wires on the SRC, REX, UCD and HCD terminals and attempt reset. If this does not restore function to the board, the board will need to be replaced.