Midmark 491 Service And Parts Manual

491

-001 thru -002

Service and

Parts Manual

Power Otolaryngology Chair

NO LONGER IN

Serial Number Prefixes: CT, DG & V

Some service parts may not

PRODUCTION

be available for this product!

FOR USE BY MIDMARK TRAINED TECHNICIANS ONLY

SF-1496 Part No. 004-0005-00 (12/06/16)

491

-001 thru

-002

TABLE OF CONTENTS

Section/Paragraph Page Section/Paragraph Page

IMPORTANT INSTRUCTIONS

General Safety Instructions......................................... ii

Safety Alert Symbols ................................................... ii

Warranty Instructions .................................................. ii

SECTION I GENERAL INFORMATION

1.1 Scope of Manual ......................................... 1-1

1.2 How to Use Manual ..................................... 1-1

1.3 Description of 491 Power Otolaryngology

Chair ......................................................... 1-1

1.4 Specifications ............................................. 1-4

1.5 Parts Replacement Ordering ....................... 1-4

1.6 Special Tools .............................................. 1-7

SECTION II TESTING AND TROUBLESHOOTING

2.1 Operational Test .......................................... 2-1

2.2 Troubleshooting Procedures ........................ 2-3

SECTION III SCHEDULED MAINTENANCE

3.1 Scheduled Maintenance .............................. 3-1

SECTION IV MAINTENANCE/SERVICE INSTRUCTIONS

4.1 Introduction ................................................. 4-1

4.2 Membrane Switch Panel Removal /

Installation ................................................ 4-1

4.3 Interface Board Removal / Installation .......... 4-3

4.4 PC Control Board Removal / Installation ...... 4-4

4.5 Back Actuator Removal / Installation ........... 4-6

4.6 Back Capacitor Removal / Installation

(Domestic Units Only) ............................... 4-9

4.7 Thrust Bearing Removal / Installation ......... 4-10

4.8 Base Actuator Removal / Installation ......... 4-13

4.9 Column Assembly Removal / Installation ... 4-17

4.10 Base Capacitor Removal / Installation

(Domestic Units Only) ............................. 4-19

4.11 Typical Capacitor Removal / Installation

(Export Units Only) ................................. 4-20

4.12 Typical Actuator Motor / Actuator Brake

Removal / Installation ............................. 4-21

4.13 Base Down Limit Switch Removal /

Installation / Adjustment ......................... 4-22

4.14 Back Up Limit Switch Removal /

Installation / Adjustment ......................... 4-24

4.15 Typical Foot Pedal Footswitch Removal /

Installation .............................................. 4-25

4.16 Arm Rest Linkage Adjustment.................... 4-26

4.17 Chair Rotational Lock Adjustment .............. 4-27

4.18 Headrest Assembly Adjustment ................. 4-28

4.19 Headrest Handles Handle Stops

Adjustment ............................................. 4-29

4.20 Column Eccentric Tires Adjustment ........... 4-29

4.21 Foot Rest Stop Adjustment ........................ 4-31

4.22 Main Harness Replacement ....................... 4-32

SECTION V SCHEMATICS AND DIAGRAMS

5.1 Electrical Schematics / Wiring Diagrams ...... 5-1

5.2 Diagnostic L.E.D. Charts .............................. 5-4

SECTION VI PARTS LIST

6.1 Introduction ................................................. 6-1

6.2 Description of Columns ............................... 6-1

6.3 Torque Specifications And Important

Assembly Notes ....................................... 6-1

Pictorial Index .............................................. 6-2

Upholstery Components ............................ 6-3(*)

Chair Frame Assembly .............................. 6-4(*)

Headrest Assembly ................................... 6-5(*)

Back Mechanism ...................................... 6-6(*)

Linkage Mechanism .................................. 6-7(*)

Back Actuator Assembly .......................... 6-8(*)

Seat Pivot Mechanism .............................. 6-9(*)

Elevation Column Assembly ................... 6-10(*)

Base Assembly ....................................... 6-11(*)

Base Actuator Assembly ........................ 6-12(*)

Receptacle Panel Assembly (Domestic) . 6-13(*)

Receptacle Panel Assembly (Export) ......... 6-14

COMMENTS ............................................................ 7-1

FAX ORDERING FORM .......................................... 7-2

(*) Indicates that there has been a serial number break for the illustration

and that there are additional point page(s) following the original page.

IMPORTANT INSTRUCTIONS

General Safety Instructions

Safety First: The primary concern of Midmark Corporation is that this chair is maintained with the

safety of the patient and staff in mind. To assure that services and repairs are completed safely and correctly, proceed as follows:

(1) Read this entire manual before performing any

services or repairs on this chair.

(2) Be sure you understand the instructions

contained in this manual before attempting to service or repair this chair.

Safety Alert Symbols

Throughout this manual are safety alert symbols that call attention to particular procedures. These items are used as follows:

DANGER

A DANGER is used for an imminently

hazardous operating procedure, practice, or condition which, if not correctly followed, will result in loss of life or serious personal injury.

NOTE

A NOTE is used to amplify an operating procedure, practice or condition.

Warranty Instructions

Refer to the Midmark “Limited Warranty” printed in the Installation and Operation Manual for warranty information. Failure to follow the guidelines listed below will void the warranty and/or render the 491 Otolaryngology Chair unsafe for operation.

• In the event of a malfunction, do not attempt to operate the chair until necessary repairs have been made.

• Do not attempt to disassemble chair, replace malfunctioning or damaged components, or perform adjustments unless you are one of Midmark’s authorized service technicians.

• Do not substitute parts of another manufacturer when replacing inoperative or damaged components. Use only Midmark replacement parts.

WARNING

A WARNING is used for a potentially

hazardous operating procedure, practice, or condition which, if not correctly followed, could result in loss of life or serious personal injury.

CAUTION

A CAUTION is used for a potentially

hazardous operating procedure, practice, or condition which, if not correctly followed, could result in minor or moderate injury. It may also be used to alert against unsafe practices.

EQUIPMENT ALERT

An EQUIPMENT ALERT is used for an

imminently or potentially hazardous operating procedure, practice, or condition which, if not correctly followed, will or could result in serious, moderate, or minor damage to unit.

SECTION I

GENERAL INFORMATION

SECTION I

GENERAL INFORMATION

1.1 Scope of Manual

This manual contains detailed troubleshooting, scheduled maintenance, maintenance, and service instructions for 491 Power Otolaryngology Chair. This manual is intended to be used by Midmark’s authorized service technicians.

1.2 How to Use Manual

A. Manual Use When Performing Scheduled Mainte-

nance. (1) Perform inspections and services listed in

Scheduled Maintenance Chart (Refer to para 3.1).

(2) If a component is discovered to be faulty or out

of adjustment, replace or adjust component in accordance with maintenance/service instructions (Refer to para 4.1).

B. Manual Use When Chair Is Malfunctioning And

Cause Is Unknown.

medical examinations and procedures on ears, noses, and throats.

The major serviceable components of the table are the PC control board, membrane switch panels, interface board, back actuator, back capacitor, base actuator, base capacitor, base down limit switch, back up limit switch, headlock assembly, elevation column assembly which includes eccentric bearings, chair rotational lock assembly, back linkage mechanism, pivot thust bearing, and foot control which includes four footswitches.

B. Theory of Operation (See Figures 5-1 and 5-2

for wiring diagrams / electrical schematics)

Electrical Power: Line voltage (115 VAC for domestic units and 230 VAC

for export units) is supplied to the chair's PC control board. There is a transformer and associated follow-on circuitry on the PC control board which reduces the line voltage to approximately 12 VDC. The 12 VDC provides power to operate the circuitry of the PC control board, membrane switch panels, and foot control.

(1) Perform an operational test on chair (Refer to

para 2.1).

(2) Perform troubleshooting procedures listed in

Troubleshooting Guide (Refer to para 2.2).

(3) If a component is discovered to be faulty or out

of adjustment, replace or adjust component in accordance with maintenance/service instructions (Refer to para 4.1).

C. Manual Use When Damaged Component Is Known.

(1) Replace or adjust component in accordance

with maintenance/service instructions (Refer to para 4.1).

1.3 Description Of 491 Power Otolaryngology Chair

A. General Description (See Figure 1-1).

The 491 Power Otolaryngology Chair is an examination chair designed specifically for performing general

On domestic units, 115 VAC is continuously supplied to the electrical receptacle. Export units do not have electrical receptacles.

Chair Operation using Switch Membranes or Hand Control:

When a manual function button is pressed, the switch membranes send signals to the PC control board using three data lines. The PC control board determines which function was selected by analyzing which data lines contained a signal and then the PC control board energizes the relay for the selected function.

There is always line voltage at the common contact (output) of the relays and there is a relay for each up and down function: BASE UP, BASE DOWN, BACK UP, and BACK DOWN. So, when a relay is energized, line voltage is applied thru the relay and then across the motor coil of the selected function, causing it to run. When the button is released, the function's relay is deenergized, removing line voltage from the motor coil which causes it to stop running. The BASE DOWN function has an additional control circuit to prevent it from being freewheeled at the end of its down travel.

SECTION I GENERAL INFORMATION

HEADLOCK

ASSEMBLY

MEMBRANE

SWITCH PANELS

EXPORT UNIT COMPONENTS

BACK

CAPACITOR

(EXPORT

UNITS ONLY)

BASE

CAPACITOR

(EXPORT

UNITS ONLY)

PIVOT

THRUST

BEARING

BACK UP

LIMIT SWITCH

INTERFACE

BOARD

ROTATIONAL

ASSEMBLY

FOOT

CONTROL

CHAIR

LOCK

BACK

LINKAGE

MECHANISM

PC CONTROL

BOARD

FOOT

SWITCHES

BASE

CAPACITOR

(DOMESTIC

UNITS ONLY)

BASE

ACTUAT OR

BACK

ACTUATOR

BACK

CAPACITOR

(DOMESTIC

UNITS ONLY)

ECCENTRIC

BEARINGS

BASE DOWN

LIMIT SWITCH

ELEVATION

COLUMN

ASSEMBL Y

MA312800

Figure 1-1. Major Components

SECTION I

GENERAL INFORMATION

When the base down limit switch is tripped, the PC control board de-energizes the base down relay causing the base actuator to stop running (even if the button is still being depressed by the operator). This prevents the base actuator from being freewheeled when it reaches the end of its down travel. Otherwise, under heavy loads, excessive wear or damage to base actuator could result.

When the AUTO RETURN button is depressed, the switch membranes send signals to the PC control board using three data lines. The PC control board determines that the AUTO RETURN function was selected and energizes two relays: the BACK UP relay and the BASE DOWN relay. The PC control board keeps these functions running even when the operator releases the button. Then, the PC control board monitors the status of the normally open (N.O.) base down limit switch and N.O. back up limit switch. The N.O. limit switches are tripped, resulting in a closed circuit, when the actuators are in all positions but their auto return home position. When an actuator reaches its auto return home position, the limit switch becomes untripped and the PC control board de-energizes the relay for that function causing its actuator to stop. When both limit switches have become untripped, stopping both actuators, the auto return function is complete. The PC control board has a backup timing circuit in case the back up limit switch or base down limit switch malfunctions during the auto return function. If the PC control board does not see the status of both limit switches change within approximately 17 seconds of actuator run time, the backup circuit shuts down the auto return function.

The STOP button may be pressed at any time during the AUTO RETURN function. When the STOP button is pressed, the switch membranes send a signal to the PC control board. The PC control board determines that the STOP function was selected and stops the auto return function. This de-energizes the base down and back up relays, stopping the actuators.

Actuator Operation: The base and back actuators are ball screw driven.

The actuator assemblies contain a pivot point on the end of the ball screw. If an actuator assembly is run to the end of its stroke, the ball screw shaft spins inside the nut, which allows the actuator assembly to run without damaging or advancing the nut.

The base and back actuators have internal braking mechanisms which disengage when the motor starts running and engage when the motor stops running.

Diagnostic L.E.D. Information There are thirteen L.E.D.'s on the PC logic board which can be used for troubleshooting aids. Table 5-1 lists all functions for this chair and which L.E.D's should illuminate when a button or footswitch is depressed. See Figure 5-3 for location of L.E.D.'s.

• The back up relay L.E.D. illuminates to indicate that the PC control board is energizing the back up relay.

• The back down relay L.E.D. illuminates to indicate that the PC control board is energizing the back down relay.

• The base up relay L.E.D. illuminates to indicate that the PC control board is energizing the base up relay.

• The base down relay L.E.D. illuminates to indicate that the PC control board is energizing the base down relay.

• The foot control back up L.E.D. illuminates to indicate that the PC control board is receiving a good signal from the back up foot switch.

• The foot control back down L.E.D. illuminates to indicate that the PC control board is receiving a good signal from the back down foot switch.

• The foot control base up L.E.D. illuminates to indicate that the PC control board is receiving a good signal from the base up foot switch.

• The foot control base down L.E.D. illuminates to indicate that the PC control board is receiving a good signal from the base down foot switch.

• The auto return back function L.E.D. illuminates to indicate that the auto return circuit for the back function is activated. The L.E.D. stays illuminated until the back function has completed its portion of the auto return cycle.

• The auto return base function L.E.D. illuminates to indicate that the auto return circuit for the base function is activated. The L.E.D. stays illuminated until the base function has completed its portion of the auto return cycle.

• There are three Data Line L.E.D.'s; data line #1 L.E.D., data line #2 L.E.D., and data line #3 L.E.D.. Different combinations of these L.E.D's illuminate to indicate if the proper input signal is being sent to the PC control board from the membrane panels or hand control.

SECTION I GENERAL INFORMATION

General Information: All actuator motors have a thermal overload switch

which will activate if the actuator assembly is run continuously. The actuator motor was not designed for continuous operation. The normal cool off period for the thermal overload switches is 10 - 20 minutes.

Each actuator motor has a capacitor which provides start up power and motor run power.

There is a 0.25 amp fuse, located on the PC control board, which provides over-current protection to the control circuitry of the PC control board.

There are two 5 amp slow blow fuses, located on the PC control board, which provide over-current protection for each function's motor (i.e, Base fuse protects base actuator motor).

On older units, there is a switch on the PC control board labeled SW1; this switch must be in the OUT position or the back up limit switch will be bypassed. On newer units, there is a jumper connector; this jumper connector must be removed or the back up limit switch will be bypassed. This prevents the back function from moving when the auto return function is selected.

1.4 Specifications

Table Top Adjustment

Rotation................................................................330°

Back Section ...................................................2 to 90°

Table Top Height (Adjustable):.................... 22.0 in. to

31.0 in.

(55.9 cm to 78.7 cm)

Table Top Speeds (@ 60 Hz.):

Back Down ....................................... 11 +/- 1 seconds

Base Up ............................................ 12 +/-1 seconds

Weight Capacity (Maximum)............. 300 lb. (136.0 kg)

Electrical Requirements:

115 VAC Unit........................... 110 - 120 VAC, 60 HZ,

12 amp, single phase

230 VAC Unit...................... 220 - 240 VAC, 50/60 HZ,

10 amp, single phase

Power Consumption:

115 VAC Unit......................................... 1440 WATTS,

12 amps @ 120 VAC

230 VAC Unit........................................ 2400 WATTS,

10 amps @ 240 VAC

Recommended Circuit:

A separate (dedicated) circuit is recommended for

this chair. The chair

electrical circuit with other appliances or equipment

unless the circuit is rated for the additional load.

should not

be connected to an

Factual data for the 491 Power Otolaryngology Chair is provided in Table 1-1. Also, see Figure 1-2.

Table 1-1. Specifications

Description Data

Weight:

Without Shipping Carton................ 350 lb (158.8 kg)

With Shipping Carton..................... 375 lb (170.0 kg)

Shipping Carton....... 32 in. "L" x 29 in. "W" x 46 in. "H"

(81.2 cm x 73.66 cm x 116.8 cm)

Dimensions (See Figure 1-2):

Table Top Length (w/ headrest........ 75 in. (190.5 cm)

Table Top Width (w/o arm rests) .... 19.5 in. (49.5 cm)

Overall Width..................................... 26 in. (66.4 cm)

1.5 Parts Replacement Ordering

If a part replacement is required, order the part directly from the factory as follows:

(1) Refer to Figure 1-3 to determine the location of

the model number and serial number of the chair and record this data.

(2) Refer to the Parts List to determine the item

numbers of the parts, part numbers of the parts, descriptions of the parts, and quantities of parts needed and record this data (Refer to para 6.1).

NOTE

Ask the Purchasing Department of the company that

owns the chair for this information. Otherwise, this

information may be obtained from the dealer that

sold the chair.

75"

TOTAL

LENGTH

SECTION I

GENERAL INFORMATION

24"

BASE

WIDTH

31"

MAXIMUM

HEIGHT

22"

MINIMUM

HEIGHT

26 1/2" WIDTH

ACROSS

ARMS

24 1/4"

SEAT

WIDTH

87°

0°

3°

POWER CORD

132"

24 1/4"

BASE

LENGTH

Figure 1-2. Chair Dimensions

FOOT CONTROL CORD

48"

MA312900

SECTION I

MIDMARK

MODEL NO.

INPUT

RATING

SERIAL NO.

491-00X

115 VAC

12 AMP 60 HZ

XX000000

MODEL

NUMBER

SERIAL

NUMBER

GENERAL INFORMATION

Figure 1-3. Model Number / Serial Number Location

(3) Determine the installation date of the chair and

record this data.

(4) Call Midmark with the recorded information and

ask for the Medical Products Technical Services Department. See back cover of this manual for the phone number or use the Fax Order Form (See page 7-2 for Fax Order Form).

MIDMARK

491

DOWN

BACK

DOWN

TABLE

MA313000

1.6 Special Tools

Table 1-2 lists all of the special tools needed to repair the chair, how to obtain the special tools, and the purpose of each special tool.

Table 1-2. Special Tool List

SECTION I

GENERAL INFORMATION

Description of Special Tool

Multimeter Commercially Available Any Type Used to perform continuity and volt age checks. Torque Wrench Commercially Available Any Type Used to t i ght en nuts or s cr ews to specified v alues .

Amp Extr act ion Tool Can be purchased from any

Manufacturer's

Name / Address / Phone

authorized Amp distributor.

Manufacturer's

Part Number

458994-2 Used to remove terminal sockets from amp

connectors.

Purpose of Special Tool

SECTION I GENERAL INFORMATION

TESTING AND TROUBLESHOOTING

SECTION II

TESTING AND TROUBLESHOOTING

SECTION II

2.1 Operational Test

In order to effectively diagnose the malfunction of the chair, it may be necessary to perform an operational test as follows:

WARNING

Refer to the Operator Manual for

complete instructions on operating the chair. Failure to do so could result in personal injury.

NOTE

The Operational Test, for the most part, only describes what should happen when the chair is operated. If the chair does something other than described, a problem has been discovered. Refer to the Troubleshooting Guide to determine the cause of the problem and its correction.

(1) Plug the chair into a grounded, non-isolated,

correctly polarized outlet, that has the proper voltage output for the chair.

(4) Repeat steps 2 and 3 on the other membrane

switch panel. If the chair has a foot control, repeats steps 2 and 3 for these controls also.

(5) Raise BASE UP function all the way up and

BACK DOWN function all the way down.

(6) Press the AUTO RETURN button, wait one

second, and then press the STOP button.

(7) Observe. The BASE DOWN and BACK UP

functions should begin to run. When the STOP button is pressed, the base and back functions

should stop running. (8) Press the AUTO RETURN button again. (9) Observe. The base actuator should lower the

table top all the way down. The base actuator

should not continue to run after table top is

completely lowered. The back actuator should

raise the back section all the way up. The back

actuator should not continue to run after back

section is raised all the way up.

(2) Press BACK UP, BACK DOWN, BASE UP, and

BASE DOWN buttons on one of membrane switch panels.

(3) Observe. The table top should move in the

direction corresponding to the button which is being depressed. No section of the table top should drift on its own after membrane switch panel button is released. No actuator assembly should make excessive squealing noises. Movement should be steady and should match the speeds and positions listed below:

Chair Speeds (@ 60 Hz.):

Back Down (Up to Down) ................. 11 +/- 1 seconds

Base Up (Down To Up) ..................... 12 +/-1 seconds

Chair Positioning

Back Section ...................................................2 to 90°

Table Top Height (Adjustable): .....................22.0 in. to

31.0 in.

(55.9 cm to 78.7 cm)

(10) Unlock the pivot brake lever and rotate the

table top as far as it will go to the left and then

to the right.

(11) Observe. The table top should be able to be

rotated for approximately 330° of rotation.

Excessive force should not be required to

rotate table top and there should not be squeal-

ing or grinding noises coming from the pivot

point.

(12) Lock the brake lever. (13) Push on table at various points of the table top. (14) Observe. The column assembly should not

have excessive play.

(15) Unlock locking handle, position headrest in a

horizontal position as shown, and then relock

locking handle.

(16) Place a 45 lb (20.4 kg) static load at Point A.

SECTION II

BACK

SECTION

AXIS

"B"

AXIS

"C"

POINT

"A"

LOCKING

HANDLE

TESTING AND TROUBLESHOOTING

MEMBRANE SWITCH PANEL

BACK UP

BUTTON

BACK

DOWN

BASE

BASE DOWN

AUTO

RETURN

STOP

BUTTON

BACK

DOWN

BUTTON

BASE UP

BUTTON

BASE

DOWN

BUTTON

AUTO RETURN BUTTON

TABLE

TOP

330°

ROTATION

DOWN

BACK

DOWN

TABLE

TABLE DOWN

BRAKE

LEVER

FOOT CONTROL

FOOT SWITCHES

BACK

DOWN

BACK

Figure 2-1. Operational Test

MIDMARK

491

FOOT REST

MA312700

SECTION II

TESTING AND TROUBLESHOOTING

(17) Observe. There should be no movement at

axis B or Axis C when the static load is applied to the headrest. The maximum force required to unclamp a locking handle should be 17 lbs. (7.7 kg) and the maximum force required to clamp a locking handle should be 35 lbs. (15.8 kg).

(18) Raise foot rest up to stowed position.

Table 2-1. Troubleshooting Guide

Problem Symptom Probable Cause Check Correction

Chair will not operate when any of the four up or down or auto return functions are selected from the membrane switch panels.

When any button is pressed, nothing happens (actuator motor(s) does not run or hum).

Nothing happens when a membrane button is pressed, but chair runs when a foot control foot switch is depressed.

(19) Observe. The foot rest should not fall down on

its own; it should stay locked in the stowed position.

2.2 Troubleshooting Procedures

Table 2-1 is a Troubleshooting Guide which is used to determine the cause of the malfunction.

Power cord is not plugged into facility wall outlet.

Facility circuit breaker providing power to chair is tripped.

Wire connections loose. Check all wiring

0.25 amp transformer primary fuse on PC control board is blown.

PC control board is malfunctioning.

Interface board is malfunctioning.

PC control board is malfunctioning.

Check to see if power cord is plugged in.

Check to see if facility circuit breaker is tripped. One way of checking this is to plug a lamp into wall outlet that chair was plugged into.

connections from power cord to PC control board. Perform continuity check on wires. Use multimeter to check for proper voltage levels.

Refer to Figure 5-1 or 5-2 for this check. Perform continuity check on primary fuse.

Replace suspect PC control board with known working PC control board or use diagnostic L.E.D. chart (Table 5-1) to determine location of malfunction.

Replace suspect interface board with known working interface board.

Replace suspect PC control board with known working PC control board or use diagnostic L.E.D. chart (Table 5-1) to determine location of malfunction.

Plug power cord into facility wall outlet.

If circuit breaker is tripped, determine what caused circuit breaker to trip, correct the problem, and then reset / replace circuit breaker.

Clean any dirty connections. Tighten any loose connections. Replace any damaged connections.

Replace blown primary fuse.

Replace PC control board. Refer to para 4.4. If PC control board is not receiving proper inputs per Table 5-1, replace interface board Refer to para 4.3.

Replace interface board. Refer to para 4.3.

Replace PC control board. Refer to para 4.4. If PC control board is not receiving proper inputs per Table 5-1, replace interface board Refer to para 4.3.

SECTION II TESTING AND TROUBLESHOOTING

Table 2-1. Troubleshooting Guide - Continued

Problem Symptom Probable Cause Check Correction

One or more functions cannot be initiated from a membrane switch panel.

One or more functions cannot be initiated from the optional foot control.

BACK UP and BACK DOWN functions do not work. All other functions work.

Some functions may be initiated from a membrane switch panel, but at least one may not. All functions can be initiated from the other membrane switch panel.

Some functions may be initiated from the foot control, but at least one may not. All functions can be initiated from the membrane switch panel.

When BACK UP and BACK DOWN buttons are pressed, the chair will not move (all other functions work).

One of the button membranes on the membrane switch panel is malfunctioning.

Interface board is malfunctioning.

Foot switch for non-operable function is malfunctioning.

PC control board is malfunctioning.

Wire connections loose. Check all wiring

Back capacitor is weak or blown.

Thermal overload switch in back actuator is activated.

5 amp BACK fuse for BACK UP and BACK DOWN functions is blown (located on PC control board).

Back actuator assembly is malfunctioning.

Wire connections loose. Check all wiring

PC control board is malfunctioning.

Refer to Table 5-1 for this check. Press each button of membrane switch panel to verify that each button causes the appropriate L.E.D.’s on PC control board to illuminate.

Replace suspect interface board with known working interface board.

Perform a continuity check on suspect foot switch.

Refer to Table 5-1 and Figure 5-3 for this check. Depress each foot switch on foot control to verify that each footswitch causes the appropriate L.E.D.’s on PC control board to illuminate.

connections from foot control to PC control board. Perform continuity check on wires. Use multimeter to check for proper voltage levels.

Replace suspect back capacitor with known working back capacitor.

- Wait 10 to 20 minutes to allow

Refer to Figure 5-1 or 5-2 for this check. Perform a continuity check on 5 amp BACK fuse.

Replace suspect back actuator assembly with known working back actuator assembly.

connections to back actuator assembly.

Replace suspect PC control board with known working PC control board.

If appropriate L.E.D’s illuminate for each button, replace PC control board. Refer to para 4.4. If not, replace membrane switch panel. Refer to para 4.2.

Replace interface board. Refer to para 4.3.

Replace foot switch. Refer to para 4.15.

If appropriate L.E.D’s illuminate for each foot switch, replace PC control board. Refer to para 4.4. If not, replace malfunctioning foot switch. Refer to para 4.15.

Clean any dirty connections. Tighten any loose connections. Replace any damaged connections.

Replace back capacitor. Refer to para 4.6 or 4.11.

back actuator motor to cool. Replace blown BACK fuse.

Replace actuator motor or back actuator assembly. Refer to para 4.12 or 4.5.

Clean any dirty connections. Tighten any loose connections. Replace any damaged connections.

Replace PC control board. Refer to para 4.4.

Problem Symptom Probable Cause Check Correction

BASE UP and BASE DOWN functions do not work. All other functions work.

BACK UP function works, but BACK DOWN function does not or BACK DOWN function works, but BACK UP function does not. All other functions work.

Table 2-1. Troubleshooting Guide - Continued

When BASE UP and BASE DOWN buttons are pressed, the chair will not move (all other functions work).

One function operates properly, but the other does not.

TESTING AND TROUBLESHOOTING

Base capacitor is weak or blown.

Thermal overload switch in base actuator is activated.

5 amp BASE fuse for BASE UP and BASE DOWN functions is blown (located on PC control board).

Base actuator assembly is malfunctioning.

Wire connections loose. Check all wiring

PC control board is malfunctioning.

Wire connections loose. Check all wiring

Back actuator assembly is malfunctioning.

PC control board is malfunctioning (relay for up or down function is malfunctioning).

Replace suspect base capacitor with known working base capacitor.

- Wait 10 to 20 minutes to allow

Refer to Figure 5-1 or 5-2 for this check. Perform a continuity check on 5 amp BASE fuse.

Replace suspect base actuator assembly with known working base actuator assembly.

connections to base actuator assembly.

Replace suspect PC control board with known working PC control board.

connections to back actuator assembly.

Replace suspect back actuator assembly with known working back actuator assembly.

Refer to Figure 5-3 for this check. Press BACK UP and then BACK DOWN button while observing the PC control board. The BACK UP RELAY L.E.D. should illuminate when the BACK UP button is pressed and the BACK DOWN RELAY L.E.D. should illuminate when the BACK DOWN button is pressed. If not, PC control board is malfunctioning.

SECTION II

Replace base capacitor. Refer to para 4.10 or 4.11.

tilt actuator motor to cool. Replace blown BASE fuse.

Replace actuator motor or base actuator assembly. Refer to para 4.12 or 4.8.

Clean any dirty connections. Tighten any loose connections. Replace any damaged connections.

Replace PC control board. Refer to para 4.4.

Clean any dirty connections. Tighten any loose connections. Replace any damaged connections.

Replace actuator motor or back actuator assembly. Refer to para 4.12 or 4.5

Replace PC control board. Refer to para 4.4.

SECTION II TESTING AND TROUBLESHOOTING

Table 2-1. Troubleshooting Guide - Continued

Problem Symptom Probable Cause Check Correction

BASE UP function works, but BASE DOWN function does not or BASE DOWN function works, but BASE UP function does not. All other functions work.

AUTO RETURN function does not work.

One function operates properly, but the other does not.

When AUTO RETURN button is pressed, nothing happens.

When AUTO RETURN button is pressed, BACK UP function does not run, but BASE DOWN function does.

Wire connections loose. Check all wiring connections to

Base actuator assembly is malfunctioning.

PC control board is malfunctioning (relay for up or down function is malfunctioning).

AUTO RETURN button on membrane switch panel is malfunctioning.

Interface board is malfunctioning.

The STOP button on membrane switch panel is malfunctioning (stuck closed).

Back up limit switch is malfunctioning (stuck open).

Older units - back bypass switch (SW1), located on PC control board, is pushed in. Newer units jumper connector is on both SW1 pins on PC control board.

PC control board is malfunctioning.

base actuator assembly.

Replace suspect base actuator assembly with known working base actuator assembly.

Refer to Figure 5-3 for this check. Press BASE UP and then BASE DOWN button while observing the PC control board. The BASE UP RELAY L.E.D. should illuminate when the BASE UP button is pressed and the BASE DOWN RELAY L.E.D. should illuminate when the BASE DOWN button is pressed. If not, PC control board is malfunctioning.

Refer to Table 5-1 and Figure 5-3 for this check. Press AUTO RETURN button of membrane switch panel and verify that the button causes the appropriate L.E.D.’s on PC control board to illuminate.

Replace suspect interface board with known working interface board.

Refer to Figure 5-3 for this check. If data line #1, #2, and #3 L.E.D.’s are all illuminated even though STOP button is not being pressed, membrane switch panel is malfunctioning.

Perform continuity check on back up limit switch. Limit switch tripped = continuity between COM. and N.O. terminals.

Refer to Figure 5-3 for this check. On older units, check to see if bypass switch (SW1) is pushed in. On newer units, check to see if jumper connector is on both SW1 pins.

Refer to Figure 5-3 for this check. After AUTO RETURN button is pressed, the auto return back function L.E.D. should illuminate and stay illuminated until the back section is all the way up.

Clean any dirty connections. Tighten any loose connections. Replace any damaged connections.

Replace actuator motor or base actuator assembly. Refer to para 4.12 or 4.8.

Replace PC control board. Refer to para 4.4.

If appropriate L.E.D’s illuminate for each button, replace PC control board. Refer to para 4.4. If not, replace membrane switch panel. Refer to para 4.2.

Replace interface board. Refer to para 4.3.

Replace membrane switch panel. Refer to para 4.2.

Replace back up limit switch. Refer to para 4.14.

On older units, pull bypass switch (SW1) to out position. On newer units, remove the jumper connector from SW1 pins and discard.

If not, replace PC control board. Refer to para 4.4. If L.E.D. does illuminate, replace interface board. Refer to para 4.3.

TESTING AND TROUBLESHOOTING

Table 2-1. Troubleshooting Guide - Continued

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SECTION II

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SECTION II TESTING AND TROUBLESHOOTING

Table 2-1. Troubleshooting Guide - Continued

Problem Symptom Probable Cause Check Correction

Chair moves fine for light patient, but will not move or moves slowly for very heavy patient.

Whirling or squeaking noise is heard when an actuator assembly is being run.

Excessive sideways play of table top.

Headrest is not operating properly.

Table top rotation is not working.

Foot rest will not lock into stowed position.

Heavy patients cause chair to malfunction.

Noisy actuator. Foreign matter on ball

Table top is not stable and can be moved from side to side.

Headrest drifts downward while supporting patients head.

Headrest locking handles pop out of locked position.

When table top is rotated, squealing noise is made and / or excessive force is required to rotate the table top.

The table top is rotating even though the pivot brake lever is in locked position.

When foot rest is raised into stowed position, it falls down by itself.

Low voltage is being supplied to chair.

Chair overloaded with too heavy of a patient.

Capacitor for suspect function is weak.

screw threads and / or lack of lubricant.

Eccentric tires are out of adjustment.

Headrest is out of adjustment.

Headrest handles handle stops need adjusted.

Thrust bearing is worn or damaged.

Chair rotational lock mechanism is out of adjustment.

Ball plungers are out of adjustment.

Check voltage at wall receptacle - should be 115 +/- 5 VAC for domestic units and 230 +/- 10 VAC for export units.

Maximum weight capacity of chair is 300 lbs (136.0 kg).

Replace suspect capacitor with known working capacitor.

Check for foreign matter on ball screw threads. Check for lack of lubricant on ball screw threads.

While observing the eccentric tires, run BASE UP function all the way up and then the BASE DOWN function all the way down. Any eccentric tires which do not come into contact with the inner column and rotate at least once during the full extension and retraction of the column assembly, need adjusted.

Check adjustment of headrest. Adjust headrest. Refer to

Check adjustment of headrest handles handle stops.

Replace suspect thrust bearing with known working thrust bearing.

Check adjustment of the chair rotational lock mechanism.

Check the adjustment of the ball plungers.

Correct low voltage situation at wall receptacle.

Inform chair operator of weight limitation.

Replace capacitor.

Clean all foreign matter off of ball screw threads. Coat ball screw threads with STP treatment oil or equivalent. If actuator assembly is still noisy, replace it.

Adjust eccentric tires. Refer to para 4.20.

para 4.18.

Adjust headrest handles handle stops. Refer to para

4.19. Replace thrust bearing.

Refer to para 4.7.

Adjust the chair rotational lock mechanism. Refer to para 4.17.

Adjust the ball plungers. Refer to para 4.21.

SCHEDULED MAINTENANCE

SECTION III

SCHEDULED MAINTENANCE

SECTION III

3.1 Scheduled Maintenance

periodically on the chair. These inspections and services should be performed as often as indicated in

Table 3-1 is a Scheduled Maintenance Chart which lists

the chart.

the inspections and services that should be performed

Table 3-1. Scheduled Maintenance Chart

Interval Inspection or Service What to Do

Semi-annually Obvious damage Visually check condition of chair for obvious damage such as: cracks in components, missing

Fasteners / hardware Check chair for missing or loose fasteners / hardware. Replace any missing hardware and

Warning and instructional decals

Pivot points / moving parts / accessories

Membrane switch panel Check that all membrane switch buttons work when pressed. If not, replace membrane switch

Foot control (optional) Check that foot control works correctly. Make sure all footswitches operate properly. Replace

Auto return function Check that auto return function works correctly. Ensure each actuator stops running when it

Ball screws of actuator assemblies

Drifting of actuator assemblies

Arm rests The arm rest should be parallel to the seat section when the back section is all the way up. If not,

Chair rotational lock Move pivot brake lever to the "locked' position and then attempt to rotate the table top. If the

Table top rotation Check that table top can be rotated 330 degrees. Rotation should be easy and noiseless. If not,

Excessive play in column assembly

Headrest Check that headrest is adjusted properly and will not drift downward on its own under 45 lbs (20.4

Electrical receptacle (Domestic units only)

Upholstery Check all upholstery for rips, tears, or excessive wear. Replace cushions as necessary. Accessories Check that all accessories have all of their components and that they function properly. If

Operational Test Perform an Operational Test to determine if the chair is operating within its specifications (Refer

components, dents in components, or any other visible damage which would cause chair to be unsafe to operate or would compromise its performance. Repair chair as necessary.

tighten any loose hardware as necessary. Check for missing or illegible decals. Replace decals as necessary.

Lubricate all exposed pivot points, moving parts, and accessories with silicone based lubricant.

panel. Refer to para 4.2.

any malfunctioning footswitches. Refer to para 4.15.

reaches its end of travel and does not "freewheel". If necessary, adjust or replace limit switches. Refer to para 4.13 or 4.14.

Extend each actuator assembly and wipe ball screw threads down with a rag to remove foreign matter. Coat as much of the ball screw threads as possible with STP treatment oil or equivalent. Run each actuator assembly to both ends of its travel a couple of times to spread the oil evenly over all of the ball screw threads and then remove excess oil. If oil does not correct a squealing actuator assembly, replace actuator assembly.

Check each actuator assembly for drift. Replace actuator assembly brake components as necessary. Refer to para 4.12.

adjust the arm rest height. Refer to para 4.16.

table top rotates, adjust the rotational lock mechanism. Refer to para 4.17.

lubricate thrust bearing with vaseline or replace thrust bearing. Refer to para 4.7. Check that column assembly is stable and does not have excessive side to side play. Observe

the eccentric tires while running the BASE function all the way up and all the way down. Any eccentric tires which do not come into contact with the inner column and rotate at least once during the full extension and retraction of the column assembly, need adjusted. If necessary, adjust and / or replace eccentric tires. Refer to para 4.20.

kg) of static weight. If necessary, adjust headrest. Refer to para 4.18. Check that the electrical receptacle is functioning properly. Replace receptacle as necessary.

necessary, repair or replace the accessory.

to para 2.1). Replace or adjust any malfunctioning components.

SECTION III SCHEDULED MAINTENANCE

MAINTENANCE / SERVICE

SECTION IV

MAINTENANCE / SERVICE INSTRUCTIONS

SECTION IV

4.1 Introduction

DANGER

Refer to the Operator Manual for

complete instructions on operating the chair. Failure to do so could result in personal injury.

NOTE

Perform an operational test on the chair after the repair is completed to confirm the repair was properly made and that

The following paragraphs contain removal, installation, repair, and adjustment procedures for the chair.

all

malfunctions were repaired.

4.2 Membrane Switch Panel Removal / Installation

A. Removal

NOTE

This art shows removal of the membrane switch panel from the patients right side of chair. Removal of membrane switch panel from patients left side of chair is the same.

(1) Raise BACK UP function all the way up. (2) Remove four screws (1, Figure 4-1) and

headrest assembly or headrest block (2) from back casting (3).

B. Installation

(1) Using warm soapy water, clean back casting

(3, Figure 4-2) in area where membrane switch panel (1) is to be installed. Allow to dry.

(2) Feed ribbon cable of membrane switch panel

(1) thru cable slot.

(3) Pull paper backing off of membrane switch

panel (1); then press membrane switch panel firmly into place on back casting (3).

EQUIPMENT ALERT

Use care not to bend, kink, or crease the

ribbon cable of the membrane switch panel. Failure to use care could result in damage to ribbon cable.

(4) Connect ribbon cable of membrane switch

panel (1) to interface board (2).

EQUIPMENT ALERT

Overtightening screws (7 and 8) could

cause back cover to crack.

NOTE

The shorter screws go on top.

(5) Install back cover (9, Figure 4-1) on back

casting (3) and secure with two long screws (8) and two short screws (7). Tighten screws until back cover starts to deform.

(3) If chair has an optional exam light assembly,

remove four screws (4) and exam light assembly (5) from light bracket (6).

(4) Remove two short screws (7), two long screws

(8), and back cover (9) from back casting (3).

(5) Disconnect ribbon cable of membrane switch

panel (1, Figure 4-2) from interface board (2).

(6) Using screwdriver, gently pry membrane switch

panel (1) off of back casting (3). Remove membrane switch panel (1) from back casting.

(6) If removed, install exam light assembly (5) on

light bracket (6) and secure with four screws (4).

(7) If removed, install headrest assembly or

headrest block (2) on back casting (3) and secure with four screws (1).

SECTION IV MAINTENANCE / SERVICE

Figure 4-1. Back Cover Removal / Installation

MA313100

SECTION IV

MAINTENANCE / SERVICE

RIBBON

CABLE

SLOT

CABLE

PAPER

BACKING

MA313200

Figure 4-2. Membrane Switch Panel

Removal / Installation

4.3 Interface Board Removal / Installation

(7) Remove four screws (4), spacers (5), interface

board (2), and light bracket (6) from back casting (7).

B. Installation

(1) Install light bracket (6), four spacers (5, Figure

4-4) and interface board (2) on back casting (7) and secure with four screws (4).

(2) Connect modular cord (3) to interface

board (2).

EQUIPMENT ALERT

Use care not to bend, kink, or crease the

ribbon cable of the membrane switch panel. Failure to use care could result in damage to ribbon cable.

(3) Connect two ribbon cables (1) to interface

board (2).

EQUIPMENT ALERT

Overtightening screws (7 and 8) could

cause back cover to crack.

A. Removal

(1) Raise BACK UP function all the way up. (2) Remove four screws (1, Figure 4-3) and

headrest assembly or headrest block (2) from back casting (3).

(3) If chair has an optional exam light assembly,

remove four screws (4) and exam light assembly (5) from light bracket (6).

(4) Remove two short screws (7), two long screws

(8), and back cover (9) from back casting (3).

(5) Disconnect two ribbon cables (1, Figure 4-4)

from interface board (2).

(6) Disconnect modular cord (3) from interface

board (2).

NOTE

Not all units have a light bracket (6).

NOTE

The shorter screws go on top.

(4) Install back cover (9, Figure 4-3) on back

casting (3) and secure with two long screws (8) and two short screws (7). Tighten screws until back cover starts to deform.

(5) If removed, install exam light assembly (5) on

light bracket (6) and secure with four screws (4).

(6) If removed, install headrest assembly or

headrest block (2) on back casting (3) and secure with four screws (1).

SECTION IV MAINTENANCE / SERVICE

Figure 4-3. Back Cover Removal / Installation

4.4 PC Control Board Removal / Installation

A. Removal

(1) If possible, raise BASE UP function all the way up.

WARNING

Always disconnect the power cord

from the wall outlet before removing any of the chair's covers/shrouds or making any repairs to prevent the possibility of electrical shock. Failure to comply with these instructions could result in severe personal injury or death.

MA313100

(2) Unplug chair power cord from wall outlet. (3) Remove four screws (1, Figure 4-5), four

screws (2), and R.H. and L.H. shrouds (3) from base mounts (4).

NOTE

Older units have a slightly different motor cover than is shown. Removal is similar.

(4) Remove two screws (5), four screws (6), and

motor cover (7) from elevation column (8).

(5) Disconnect three wire harnesses (1, Figure 4-

6) from PC control board (2).

SECTION IV

MAINTENANCE / SERVICE

(6) Tag and disconnect two modular cords (3) from

PC control board (2).

(7) Loosen five terminal screws (4); then tag and

disconnect five wires (5) from PC control board (2).

Figure 4-4. Interface Board Removal / Installation

MA313300

NOTE

There are two jumper strips which may fall off of terminal strip during disconnection of wires. Do not lose.

(8) Remove four screws (6), spacers (7), and PC

control board (2) from elevation column (8).

B. Installation

(1) Install PC control board (2, Figure 4-6) on

elevation column (8) and secure with four spacers (7) and screws (6).

MIDMARK

Figure 4-5. Shrouds and Motor Cover Removal / Installation

491

MA313400

SECTION IV

JUMPER

STRIP

MAINTENANCE / SERVICE

(5) Connect three wire harnesses (1) to PC control

board (2).

EQUIPMENT ALERT

On older units, SW1 usually gets pushed

in when top wire harness is connected. SW1 must be in pulled out position for table to function properly.

(6) On older units, check position of SW1 (9). If

SW1 is not in pulled out position, pull SW1 out. On newer units, check to make sure jumper connector (9A) is not installed. If installed, remove jumper connector from SW1 pins (9B).

(7) Install motor cover (7, Figure 4-5) on elevation

column (8) and secure with four screws (6) and two screws (5).

(8) Install R.H. and L.H. shrouds (3) on base

mounts (4) and secure with four screws (2) and four screws (1).

Figure 4-6. PC Control Board Removal / Installation

(2) Make sure two jumper strips are installed on

terminal strip and did not fall out during wire disconnection.

(3) Connect five wires (5) to PC control board (2)

and secure by tightening five terminal screws (4).

(4) Connect two modular cords (3) to PC control

board (2).

(9) Plug chair power cord into wall outlet.

4.5 Back Actuator Removal / Installation

A. Removal

WARNING

Always disconnect the power cord

(1) Unplug chair power cord from wall outlet.

MA313501

SECTION IV

EARLY

UNITS

LA TER

UNITS

MAINTENANCE / SERVICE

(2) Remove upholstered seat section (1, Figure 4-

7) from seat casting (2) and upholstered back section (3) from upholstered back casting (4).

(3) Remove three screws (5) and seat cover (6)

from seat casting (2).

MIDMARK

491

Figure 4-7. Wires Disconnection / Connection

MA313600

SECTION IV MAINTENANCE / SERVICE

(4) On chairs with Serial Numbers CT-1000 thru

CT-1354 and DG-1000 thru DG-1099, perform the following steps:

a. Remove screw (7), ground wire (8), and

star washer (9) from seat casting (2).

b. Disconnect wire harness (10) from wire

harness (11).

(5) On chairs with Serial Numbers CT-1355 thru

Present and DG-1100 thru Present, perform the following steps:

a. Remove screw (12), ground wire (13), and

starwasher (14) from seat casting (2).

b. Disconnect wire harness (15) from wire

harness (16).

NOTE

If back actuator is being discarded, its three wires can be cut. If the back actuator is being removed for repair, an amp tool must be used or damage to socket terminals will result.

c. Using an amp tool, push three socket

terminals (17) from plug (15). See Table 1-2 for special tool.

d. Remove two screws (18) and strain relief

bracket (19) from seat casting (2).

e. Remove strain relief bushing (20) from

strain relief bracket (19).

f. Pull back actuator wires (21) from strain

relief bracket (19).

g. Remove strain relief bushing (20) from

back actuator wires (21).

(6) Cut cable tie (1, Figure 4-8) securing limit

switch wires (2) to shaft of back actuator (3).

(7) Remove two screws (4), lockwashers (5), and

separate limit switch bracket (6) from shaft of back actuator (3).

Figure 4-8. Back Actuator Removal / Installation

MA313700

CAUTION

Push arm rests out of the way or support

them while removing clevis pin. The arm rest will be free to fall, possibly resulting in minor injury to technician.

(8) Remove rue ring cotter pin (7) and clevis pin (8)

securing linkage assembly (9) to shaft of back actuator (3).

(9) Remove screw (10) and washer (11) securing

push rod assembly (12) to leg casting (13).

+ 72 hidden pages

Midmark 491 Service And Parts Manual

Specifications and Main Features

Frequently Asked Questions

User Manual