"My name is Billy Walker "MediTek UK Technical Support" based at our new Newton Aycliffe UK Manufacturing Facility. 

I have worked for MediTek since 1996 in many roles giving me an in depth knowledge of all the products we have ever made.

I am asked many  technical questions and as a result I have compiled a handbook containing those FAQ.

This handbook has proved so popular with my dealers over the years they have christened it ' Billy's Bible'

I hope it helps........."

Billy's Bible

What is the problem?

 Power problem? – the system won’t switch on: Go to power problem section

 Safety Circuit? - the lift won’t move and there is a message on the display: Go to safety circuit section

 A battery charging problem?-the batteries won’t charge: Go to charging section

 Auxiliary problem? - a problem with a hinge or powered swivel: Go to auxiliary section

 No Drive? – A call is put in but there is no drive or intermittent drive: Go to the no drive section.

Problem Solving: The Power Section

If the lift will not switch on, the display is blank or the display shows “switched off" please read on.

If the display has any another message please go to the safety circuit section.

 Is Power getting to the PCB?

 First the obvious stuff, sorry but we have to check.

  • Is the battery is connected?
  • Does the battery have some charge in it? (At least 20V)
  • Is the battery fuse blown?
  • Is the main switch on? (It is located on the upside of the lift)
  •  If all the above are OK please check the voltage between the B+ and Gnd terminal on the PCB. 
  •  You should see battery voltage. If you do go to next section. If you don’t go back and do the obvious check again.
  • If the LCD Display shows “Switched off” go to Arm Display showing “Switched off” section.
  • If the display has any other message go to section safety circuit section.
  • If the Arm Display is blank read on. Look at the left side of the main PCB. Is there a red light next to LED 2?

If not check the connections and wire between the Arm PCB and the Main PCB.

If LED2 is on it means we have a fault in the data bus power supply. It is the red wire in the Data bus. The data bus runs all over the lift. It connects the Arm PCB to the main PCB passing through a PCB under the seat. It also connects the battery charger (and hinge PCB if fitted) to the lift via the sliding contacts on the rail. The best way to track down the fault is to disconnect everything that is connected to the data bus, one bit at a time. After each disconnection check the LED. If it goes out you have removed the fault and so know where it is.

 Things to disconnect from the Data Bus: -

 Pull the positive (red) sliding contact off its copper strip. If the LED goes off the fault is on the rail or the hinge PCB (if fitted) Check the hinge PCB by disconnecting it. If the fault is on the hinge board replace it. Otherwise check the rail and battery charger for a wiring fault between the copper strip and the rail or the Battery charger positive wire and rail.

Disconnect the Data Bus connection to the seat from the Main PCB. If the LED goes off the fault is in the seat. Reconnect the Data Bus connection and disconnect first the seat PCB then the Arm PCB to determine the location of the fault. The holding switch wiring may also need to be checked.

Arm Display Showing “Switched off”.

This means that power is getting to the Arm Board but the communication with the Main PCB is not working. This is probably caused by something being switched off but can be a fault with the Data Line

This display will be shown if the battery charger is on but the battery is disconnected or isolated. So check that the lift is turned on and the battery is connected to the main PCB. All the checks in the “Is Power getting to the PCB?” section are relevant. If you turn off the battery charger and the display goes out you defiantly have an isolated battery.

  • If you turn off the battery charger and the display goes blank go to section Is Power getting to the PCB?If you turn off the battery charger and the display continues to display “switched off” you have a problem with the data connection so read on.

 The Data line is the white wire in the data bus. It runs all over the lift. It connects the Arm PCB to the main PCB passing through a PCB under the seat.

 The key switch in the arm breaks the data line. Check it is in the “ON” position. This is almost always the cause of a break in the data line.

 Pull the Data (white) sliding contact off its copper strip. If the display starts working the fault is on the rail or the hinge PCB (if fitted). Check the rail for a wiring fault between the copper strip and the rail or between the hinge wiring and the rail.

 As its name suggests the data wire carries digital data that connects all of the PCBs in the system together allowing them to exchange information. If you measure the voltage on a working data line you should measure approximately half the battery voltage (typically 13-14 V). If you read 0V you are looking for a fault to ground (this includes the lift chassis and the rail). If it is at battery voltage the fault is to battery positive.

 The data bus is routed to the arm PCB from the main board via the seat PCB. This is the seat auxiliary PCB if fitted or a small PCB that acts as a connector between the two harnesses. Both are located under the front of the seat squab. If you disconnect either connection to the seat PCB you will lose the connection to the arm PCB. It is however possible to use a closed harness to connect the arm PCB straight to the main PCB to eliminate the seat PCB and the seat wiring from your enquiries.

Safety circuit section

 Assuming the system is switched on; the system is designed so that when you put a call in one of two things will happen.

(If the lift it isn’t switched on go to power problem section)

 1.       Either the lift will move (after a continuous warning tone).

2.       Or the lift will not move (after a series of rapid beeps).

 If the lift does not move the arm display will always indicate why. This section looks at the possible causes of these problems.

 A few points:

  • The lift will only ever display one fault at a time, usually the most serious.
  • In lifts produced Jan 2013 on wards the Real-Time Diagnostic Display (the last display in the menu system) will display the state of all the safety edges and controls in real-time. This is the display you need to use to diagnose any safety circuit or control fault.
  • Finally the fault may be that the lift is not receiving a call in the first place. You need to look at the real-time display as you put a call in.

 Faults and safety circuit trips are logged on the Primary PCB. These logs can be accessed from the menu system.

  •   On the older system (pre Jan 13) holding down the red button on the Primary PCB will reset all counters including the service counter and excluding the trip counter.
  • On the new menu system (Jan 13 onwards), the logs can be reset individually by selecting the log with the right button and resetting with the left button.  

 Roller Limit Switches/OSG Circuit

      Standard Display           

          The safety circuit monitors two switches on the lift.

 1.   The final limit switch which is the center of the three switches under the lower end of the chassis that run along the rail. The final limit is triggered if the lift over runs the normal stop points.

 2.  The over speed governor switch is mounted on the automatic brake that stops the lift if it descends too quickly.

 If either of these switches operates something is seriously wrong with the installation so the control system will lock out further operation.

Both switches operate in such a way as to lock them into the off position so the lift usually has to be hand wound to release the triggered switch.

 When the lift reaches the bottom (or top) of the rail it is stopped by the outer two of the three switches under the chassis that run along the top face of the rail. This is the control system saying you can go no further.

 If you are not at the bottom or the top of the rail and get this message obstructions on the rail could be operating the switches before the rail end, so check the switches are clear. Otherwise it is a short direct harness between the board and the switches so the connections or the switches themselves are the only likely cause of a problem.

Pressure Sensitive Edges

    The lift has many pressure sensitive edges that stop the lift if it encounters an obstruction.

 They are on either side and under the chassis and on either side and under the footrest. They only stop the lift traveling in the direction of the sensitive edge. The bottom of the footrest prevents the lift moving down.

 The standard display will show which sensitive edge has been triggered but will only remain on as long as the call is present.

 Sensitive edges can stick so check they are moving freely.

 Wiring harnesses are again short and simple so wiring problems are unlikely but check all connections are on firmly and the connector is firmly on the main PCB.

Other Safety Switches

           Standard Display   

 The seat must be locked in the travel position before the lift will move. This display indicates that the control system does not think it is.

 If you think the seat is locked correctly first check the alignment of the seat switch. It is located at the top of the seat post and should be adjusted so the cam on the seat closed the switch as the seat is centered.

 The wiring to the seat switch is some of the most vulnerable on the lift so check also for the wires being caught in the seat or seat post and check the switch itself.

                 Standard Display                              Real-Time Display not applicable            

 The Holding Switch is located on top of one of the seat arms on the opposite side to the display. It is used to lock out the whole system. Make sure that this switch is in the correct position. A break in the wires connecting this switch to the arm PCB would also cause this fault. If there was a short to earth on this circuit the whole system will shut down, the display would be blank and showing a red LED on the Primary PCB.

                  Standard Display                        Real-Time Display not applicable

 The Tilted Arm feature was added to all lifts from Jan 2013 onwards. This will lockout functions from the on-board toggle switch control only when the arm is in the up position. Remote controls will still work as normal so that the lift can be parked whilst in the folded position.

 Lift Handing Error

 

        Standard Display                              Real-Time Display not applicable

 This fault only applies to the jumper setup system prior to Jan 2013 lifts.

The control system must know what side of the stairway the lift is mounted on to operate correctly. A left hand installation is one with the lift on the left when looking up the stairs. There is a jumper on the control board to set the hand. This error message is shown if the jumper is not fitted.

 A total shutdown of the system power will reset this fault once the jumper has been replaced.

There is no error message if the link is fitted incorrectly but powered options will not work at the correct time with the wrong hand selected.

 Lifts produced from Jan 2013 onwards use the menu system to adjust the hand of the lift.

Arm Controls/Call and Send

 The system is controlled primarily by the Arm PCB however there are also local inputs on the Primary PCB which are now used for an RF control input.

 ·         The older system (pre Jan 13) will allow control input from the local inputs on the Primary PCB regardless if an Arm PCB is present on the system.

 ·         The new system (Jan 13 onwards) will not allow any control unless an Arm PCB is present on the system (this is due to the addition of the tilt switch and holding switch safety circuits on the seat arms).

 Arm PCB Controls

 This PCB is located at the end of the arm housing. It has an LCD display that shows the system status, can provide error messages and can display the system log. The Arm PCB is fitted with two IR receivers to detect remote control signals and is connected to the joystick toggle control. It communicates with the main PCB via the data bus.

  • If there is an intermittent connection from the data bus on the Primary PCB to the Arm PCB the drive of the carriage will be interrupted from the toggle control and/or the IR controls. Check the data bus wiring.
  • There may be an issue with the toggle wiring or the toggle itself.

 If LED2 is on it means we have a fault in the data bus power supply. It is the red wire in the Data bus. The data bus runs all over the lift. It connects the Arm PCB to the main PCB passing through a PCB under the seat. It also connects the battery charger (and hinge PCB if fitted) to the lift via the sliding contacts on the rail. The best way to track down the fault is to disconnect everything that is connected to the data bus, one bit at a time. After each disconnection check the LED. If it goes out you have removed the fault and so know where it is.

 Things to disconnect from the Data Bus: -

 Pull the positive (red) sliding contact off its copper strip. If the LED goes off the fault is on the rail or the hinge PCB (if fitted) Check the hinge PCB by disconnecting it. If the fault is on the hinge board replace it. Otherwise check the rail and battery charger for a wiring fault between the copper strip and the rail or the Battery charger positive wire and rail.Disconnect the Data Bus connection to the seat from the Main PCB. If the LED goes off the fault is in the seat. Reconnect the Data Bus connection and disconnect first the seat PCB then the Arm PCB to determine the location of the fault. The holding switch wiring may also need to be checked. 

Arm Display Showing “Switched off”.This means that power is getting to the Arm Board but the communication with the Main PCB is not working. This is probably caused by something being switched off but can be a fault with the Data Line 

This display will be shown if the battery charger is on but the battery is disconnected or isolated. So check that the lift is turned on and the battery is connected to the main PCB. All the checks in the “Is Power getting to the PCB?” section are relevant. If you turn off the battery charger and the display goes out you defiantly have an isolated battery.

  • If you turn off the battery charger and the display goes blank go to section Is Power getting to the PCB?
  • If you turn off the battery charger and the display continues to display “switched off” you have a problem with the data connection so read on. 

The Data line is the white wire in the data bus. It runs all over the lift. It connects the Arm PCB to the main PCB passing through a PCB under the seat. 

The key switch in the arm breaks the data line. Check it is in the “ON” position. This is almost always the cause of a break in the data line. 

Pull the Data (white) sliding contact off its copper strip. If the display starts working the fault is on the rail or the hinge PCB (if fitted). Check the rail for a wiring fault between the copper strip and the rail or between the hinge wiring and the rail.

 As its name suggests the data wire carries digital data that connects all of the PCBs in the system together allowing them to exchange information. If you measure the voltage on a working data line you should measure approximately half the battery voltage (typically 13-14 V). If you read 0V you are looking for a fault to ground (this includes the lift chassis and the rail). If it is at battery voltage the fault is to battery positive. 

The data bus is routed to the arm PCB from the main board via the seat PCB. This is the seat auxiliary PCB if fitted or a small PCB that acts as a connector between the two harnesses. Both are located under the front of the seat squab. If you disconnect either connection to the seat PCB you will lose the connection to the arm PCB. It is however possible to use a closed harness to connect the arm PCB straight to the main PCB to eliminate the seat PCB and the seat wiring from your enquiries.                                     

Pressure Sensitive Edges

         Standard Display     

 The lift has many pressure sensitive edges that stop the lift if it encounters an obstruction.

 They are on either side and under the chassis and on either side and under the footrest. They only stop the lift traveling in the direction of the sensitive edge. The bottom of the footrest prevents the lift moving down.

 The standard display will show which sensitive edge has been triggered but will only remain on as long as the call is present.

 Sensitive edges can stick so check they are moving freely.

 Wiring harnesses are again short and simple so wiring problems are unlikely but check all connections are on firmly and the connector is firmly on the main PCB.

 If the display shows “SWITCHED OFF” please go to Arm Display showing “Switched off” section.

  • If the green light on the charger is flashing quickly go to charge ground short.
  • If the display is blank please go to the go to power problem section.
  • If the display is showing “BATTERY CRITICAL” please go to the battery critical section.
  • If the lift is showing “OFF CHARGE” please read on.

 If the display is showing “OFF CHARGE” then we can assume that we have power to the system from the batteries however the main PCB is not detecting a voltage from the charger. There should also be an intermittent audible sound from the PCB.

  • The obvious first – is the charger switched on and showing a green light?
  • If the green light is not showing on the charger then please check the fuse and mains power supply to the charger.
  • Next disconnect the pickup charge connector from the data bus on the Primary PCB and take a voltage reading from the red wire of the pickup connector. There should be a reading of around 27.5vdc.
  • If you do have a reading of 27.5v from the positive pickup connection then go to lift earth section.
  • If you have a reading of less than 27.5v then you have a problem with the charge circuit read on.

 The first thing to check should be the charger itself.

  •  Disconnect the charger from the system and take a voltage reading from the charger output wires. It should read (around)  27.5V. If it does not you have a faulty charger and need to replace it.
  • If you do have 27.5 V from the charger the next step is to follow the charge system and check that there is continuity right through to the Primary PCB.
  • Start from the connecter block on the rail and check for continuity from there to the copper charge strip. You should get a reading of virtually zero ohms showing that there is no resistance. If there is resistance then there may be a bad connection somewhere on the rail lead positive. Perform the same check from the copper to the pickup pin and finally from the pin to the PCB connector. Bear in mind that the pickup pins are prone to wear especially if they have not been serviced regularly. Also a buildup of dirt on these pins can cause resistance between the contacts.

Charge Ground Short

 What also needs to be checked is if the positive side of the circuit has a short to ground. This will be highlighted if the charging unit green light is flashing quickly. To check for this disconnect the charger from the power supply and isolate the batteries. Follow the system circuit and check for continuity between each part of the circuit and ground.

 You should not have any continuity between the positive side of the charge circuit and ground.

 Lift Earth Section

 The control system battery negative is linked to the B- connection on the Primary PCB.  The system is then earthed from the B- connection on the Primary PCB via the yellow/green earth wire which is attached to the gearbox. It then earths through the rail which the charger negative is linked to through the rail lead negative

 If there is any resistance on this route then the lift will not charge properly. If you have a charging issue the earth must be checked for continuity to ensure there is no resistance.

  • Check for continuity from the battery negative to B- on the Primary PCB, from there to the gearbox, from the gearbox to the rail and from the rail to the charger.
  • You should get a reading of virtually zero ohms showing that there is no resistance. If there is then there may be a bad or corroded connection somewhere.

 Battery Critical

 If the display is showing “BATTERY CRITICAL” this means that the voltage in the batteries has dropped below 20vdc.

  • This fault can occur if input power to the Primary PCB is lost during upward travel. Please refer to the power problem section.
  • This state could signify that there is a charging issue. Please refer to the charging section.
  • If the charge system is fine then the batteries themselves may be worn out. Please change the batteries and ensure all the checks from the charging section have been carried out.

 Auxiliary Section

 The control system supports two powered options, Powered Seat Swivel and Folding Hinge Track.

 A single auxiliary PCB supports both options, its function being selected by a PCB jumper marked “SEAT” and “HINGE”. If these jumpers are selected incorrectly the system will not work as it should. If the jumper is not connected at all then the options won`t operate at all.

 The option PCBs are connected to each other and the main PCB in parallel using the data bus three wire harness.

 The connections are:-

 1.       Negative supply (black). This is the system battery negative and ground connection. For the connection to the Hinge and Platform options PCBs this signal is carried in the rail as a ground.

 2.      Positive Supply (red). This is the battery voltage supply to power the options motors. For the connection to the Hinge and Platform options PCBs this signal is shared with the Battery Charge line on the UPVC Carrier. Circuitry on the Control PCB allows the battery support the Battery Charger if the load imposed by the options PCBs is too high for the Battery Charger Supply.

 3.        Data Line (white). This is a two way communication channel controlled from the main PCB used to send and receive data to and from all options PCBs. For the Hinge PCB this signal is sent down a copper strip on the side of the rail via a pickup pin. A voltage of around 13Vdc should be present on this line which is actually a fast pulse from 27-0Vdc however a multimeter will show an average of this.

 Hinge System

 The control system must be set to “HINGE ON”.

  • On the older system (pre Jan 13) this is set by means of a jumper on the Primary PCB.
  • On the new menu system (Jan 13 onwards), use the right menu button on the Primary PCB to select “HINGE” then use the left button to set to “ON”.

 When a down call is made the Primary PCB will ask the auxiliary PCB if the hinge interlock switch circuit is closed. If not it will hold the carriage and power the hinge actuator until the interlock is activated indicating that the hinge mechanism is now closed. Only then will the carriage travel down.

 If this operation does not complete, the carriage will stay on hold showing “HINGE OPEN” on the display.

 Things to check:

  • Ensure the jumper selection is present and correct.
  • Is the hinge mechanism already closed? If so there may be an issue with the setting of the interlock switch which can be adjusted.
  • Check for continuity through the hinge interlock switch by disconnecting the two wires from the Aux PCB connectors marked “SWITCH” and test accordingly. A broken wire or bad connector could be the issue.
  • Check that there is a voltage of around 27.5Vdc from the switch spade connectors on the Aux PCB. If you do not have voltage here you may not have any power to the Aux PCB so check the red and black power connections from the rail connector block to the Aux PCB data bus Molex connector.
  • If the data line on the hinge system is broken or there is a bad connection the display with show “HINGE OPEN”. This means that the Primary PCB cannot “see” the Auxiliary PCB. Check that you have continuity on the white data line from the Molex connector on the Aux PCB to the rail connector block. Continue this check through to the copper strip, pickup pin through to the Primary PCB Molex connector ensuring you have no resistance (virtually 0ohms). As with the charge pickup pins the hinge data pickup pins are prone to wear and buildup of dirt if not serviced regularly.
  • Check that you have voltage from the Aux PCB “MOTOR” connectors when a down call is put in. The actuator wiring, connectors or the actuator itself could be at fault. Check that there are no faults to ground or short circuits between the wires. If voltage is present then check the polarity of the connections or try to run the actuator from an external source such as a spare battery.
  • In addition the hinge system has an audio visual alarm which is connected to the actuator wiring and leads out of the bottom of the rail and will attach to a wall or fixture near the hinge mechanism. This should also be checked for short circuit.

 Powered Swivel Seat

 If an up call is recycled when the carriage is on the top terminal limit the Swivel Open signal will be sent to the Power Swivel PCB. This will occur after a delay of 1 second from the new up call. The output will remain on until the call is lost. NOTE; an up call held after the carriage’s arrival at the top terminal limit will not activate the Swivel Open.

 When a Down Call is received and the Seat Swivel is open the Swivel Closed signal will be sent to the Power Swivel PCB. The output will remain on until the call is lost. After closure of the seat swivel safety circuit the call must be recycled before carriage movement is allowed.

 The power swivel feature will operate in both directions independent of the status of the hinge interlock.

 Things to check:

  • Ensure the jumper selection is present and correct.
  • The actuator wiring, connectors or the actuator itself could be at fault. Check that you have voltage from the Aux PCB “MOTOR” connectors when a call is put in. If voltage is present then check the polarity of the connections or try to run the actuator from an external source such as a spare battery.
  • Check that the seat interlock switch is set it the correct position.
  • Check the seat interlock switch wires as these are some of the most vulnerable on the system.
  • Issues with the data bus connection would cause the issues explained in the power problem section or switched off section.

 Drive Fault Messages

 Brake Fault

The control system monitors the connection to the brake. If the brake becomes disconnected from the control board, a break wire fails or if the brake itself goes open circuit this is the fault shown.

 It is obviously a serious fault so operation is locked out.

 Motor Fault

The control system uses the motor to control the speed of the lift and may actually use the motor as a brake when moving down to stop the lift going too fast. 

It is therefore useful to know if the motor has become disconnected from the control board and this is the display shown when disconnection is detected.

 An open circuit motor winding will also cause this fault to be shown.

 If the control system starts to drive the motor and the motor does not turn this display is shown.

 It is also a potentially serious fault so operation is locked out.

 Relay fault

 This indicates that the drive relay has not closed or is stuck in in the open state. A replacement Primary PCB will be required if this fault cannot be cleared.

 Overcurrent

 This fault occurs when the motor drive is overloaded. This can occur is the lift is used beyond its rated weight limit and will also occur if the lift has stalled due to an obstruction. This will protect the Primary PCB from damage to the drive circuit.

 Overspeed

 This fault occurs if:

  • The lift begins to travel down beyond the allowed speed threshold. This can occur if the lift is used beyond its rated weight limit.
  • If the power supply to the Primary PCB is lost during downward travel. Please refer to the power problem section.

 A total recycle of the system power will reset these drive faults once the issue has been solved.

 Arm Controls/Call and Send

The system is controlled primarily by the Arm PCB however there are also local inputs on the Primary PCB which are now used for an RF control input.

  • The older system (pre Jan 13) will allow control input from the local inputs on the Primary PCB regardless if an Arm PCB is present on the system.
  • The new system (Jan 13 onwards) will not allow any control unless an Arm PCB is present on the system (this is due to the addition of the tilt switch and holding switch safety circuits on the seat arms).

  IR Handsets

 Two IR remote handsets are supplied with each system. The PCB`s are supplied in an enclosure with two control buttons “up” and “down”. Two AAA batteries are needed to power each handset.

 The handsets are fitted with jumper connectors allowing the user to select one of 4 different channels. A corresponding jumper is also fitted on the main PCB on older models and be means of the menu system from all lifts and PCB`s from Jan 2013 onwards. This will allow up to four lifts to be used in the same area without the operation of one causing spurious operation of the others.

  • On all lifts from Jan 2013 onwards extra IR sensors have been added to the chassis in addition to the two on the Arm PCB to improve reception of the IR call signal.
  • If the channel selection on the Primary PCB does not match the channel selection on the remote handsets the lift will not run by these means.

 RF Handsets

 Two RF remote handsets can be supplied as an option with each system. The PCB`s are supplied in an enclosure with two control buttons “up” and “down”. One

9V battery is needed to power each handset.

 The receiver unit is a separate box which receives its power input by integrating into the B+ and B- on the Primary PCB. This ensures that the system is switched off with the battery isolator.

 Inside the receiver box and inside the handsets are a set of dip switches that can be set to four different combinations relating to the four remote channels. This will allow up to four lifts to be used in the same area without the operation of one causing spurious operation of the others.

  • If the channel selection on the Primary PCB does not match the channel selection on the remote handsets the lift will not run by these means.

 Service Due

 This indicates that the lift is due for a service. The service counter counts from 6000 trips down to zero. 

  • The service trip log can be reset on the old system by holding the red button on the Primary PCB for around 10 seconds (this resets the whole system log with the exception of the trip counter).
  • The service trip log can be reset on the new menu system (Jan 13 onwards) by selecting the service counter in the menu with the right button on the Primary PCB and the pressing the left button to zero the counter (all logs on this system can be reset individually). 

This is separate from the trip log which counts the total number of trips and cannot be reset. A trip is logged if the lift travels in any direction continuously for longer than 5 seconds and the reaches a limit stop. This means that if the lift needs to be parked for example if a hinge is present a trip is not logged.