Medi-Therm III Service Manual July 1998

CONTENTS

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SERVICE MANUAL Medi-Therm II

CONTENTS Section 1.0 2.0 3.0 3.1 3.2 4.0 4.1 4.2 4.3 5.0 6.0 6.1 6.2 6.3 6.4 7.0

Description

Page

7.1 7.2 7.3 7.4 8.0 8.1 8.2 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 10.0 10.1 10.2 11.0

PATIENT SAFETY ... 1 MACHINE PRECAUTIONS ... 3 REPAIR POLICY ... 4 In-Warranty Repairs ... 4 Out-of-Warranty Repairs ... 4 SPECIFICATIONS ... 5 Physical Specifications ... 5 Thermal Specifications ... 5 Electrical Specifications ... 6 PROBE INFORMATION ... 7 THEORY OF OPERATIONS ... 9 Machine ... 9 Interconnections ... 11 Power Supply ... 12 Machine Functions ... 12 FUNCTIONAL CHECK, SAFETY INSPECTION, PREVENTIVE MAINTENANCE ... 18 Receiving Inspection ... 18 Cleaning Procedures ... 18 Functional Check & Safety Inspection ... 20 Inspection Form ... 33 TROUBLESHOOTING & SERVICE MODES ... 34 Service Modes ... 34 Troubleshooting Charts ... 38 REPAIR PROCEDURES ... 57 Refrigeration System ... 57 Replacing the Power Supply Board ... 60 Replacing the Control/Display Board ... 61 Replacing the Top Cover ... 62 Replacing Thermostats ... 62 Cleaning the Flow Switch ... 63 Replacement Parts ... 64 Shipping/Repacking Instructions ... 64 REFERENCE TABLES ... 65 Celsius-Fahrenheit Conversion ... 65 Temperature vs. Resistance ... 66 SERVICE INFORMATION ... 67

Table

Description

TABLES 1 2 3 4 5 6 7 8 9 10

Page

High Temperature Limits ... 25 RFU Error Codes ... 35 Service Modes ... 36 Celsius/Fahrenheit Conversion ... 65 Temperature vs. Resistance ... 66 Operator Controls/Indicators ... 69 Parts List (base) ... 75 Parts List (head) ... 76 Control/Display Board Parts List ... 83 Power Supply Board Parts List ... 84

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SERVICE MANUAL Medi-Therm II

ILLUSTRATIONS

ii

Figure

Description

Page

1 2 3 4 5 6A/6L 6A 6B 6C 6D 6E 6F 6G 6H 6H 6I 6I 6J 6K 6K 6L 6L 6L 7 8 9 10 11 12 13 14 15 16 17 17A 18 19 20 21 22 23 24 25

Typical Warm-up Rate ... 6 Typical Cooldown Rate ... 6 Medi-Therm II System ... 8 MT590 Test Tool ... 24 Initiating Service Mode 1 ... 35 Troubleshooting Charts ... 38 Accessing RFU Codes ... 38 RFU Code 1 ... 39 RFU Codes 2, 3, – , E, and L ... 40 RFU Codes 4, 5 ... 41 RFU Codes 6, 7 ... 42 RFU Code 8 ... 43 RFU Code 9 ... 44 RFU Code H (page 1 of 2) ... 46 RFU Code H (page 2 of 2) ... 47 Check Water Flow Alert is On (page 1 of 2) ... 48 Check Water Flow Alert is On (page 2 of 2) ... 49 Pump Motor Not Running ... 50 Blanket Won't Heat in Auto or Manual Mode (page 1 of 2) ... 52 Blanket Won't Heat in Auto or Manual Mode (page 2 of 2) ... 53 Blanket Will Not Cool (page 1 of 3) ... 54 Blanket Will Not Cool (page 2 of 3) ... 55 Blanket Will Not Cool (page 3 of 3) ... 56 Flow Switch ... 63 Circuit Boards and Connectors (head) ... 67 Operator Controls/Indicators ... 68 Heating Flow Diagram ... 70 Cooling Flow Diagram ... 70 Refrigeration Flow Diagram ... 71 Test Setup ... 72 Machine Disassembly ... 73 Parts Diagram (base) ... 74 Parts Diagram (head) ... 76 Original Thermostat Wiring Diagram ... 77 New Thermostat Wiring Diagram ... 77 System Wiring Diagram ... 79 Control/Display Board Schematic (sheet 1 of 2) ... 80 Control/Display Board Schematic (sheet 2 of 2) ... 81 Power Supply Board Schematic ... 82 Control/Display Board ... 83 Power Supply Board ... 84 Control/Display Board Block Diagram ... 85 Shipping/Repackaging Instructions ... 86

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FIGURES

1.0

PATIENT SAFETY

PATIENT SAFETY

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SERVICE MANUAL Medi-Therm II

Use the Medi-Therm II Hyper/Hypothermia machine only under the direction of a physician. Review the following precautions and procedures prior to each application:

DANGER Do not use the Medi-Therm II machine in the presence of flammable anesthetics. Risk of explosion can result.

WARNING •

If the patient’s temperature is not responding or does not reach the prescribed temperature in the prescribed time or deviates from the prescribed temperature range, notify the attending physician promptly. Failure to notify the physician promptly may result in death or serious injury.

•

Power interruption will cause the Medi-Therm II machine to go into a standby mode, resulting in no therapy to the patient. Follow instructions for desired mode to resume operation. Failure to resume therapy could result in death or serious injury.

•

The Medi-Therm II machine is provided with a means of checking rectal/esophageal temperature probes. When performing the probe check, use a disposable protective sheath (Becton-Dickinson catalog 3700 oral sheath or equivalent) on the probe. Failure to use sheath could result in cross-contamination.

•

A physician’s order is required for setting blanket temperature and for continued use of equipment. At least every 20 minutes, or as directed by a physician, check patient’s temperature and skin condition of areas in contact with blanket; also, check blanket water temperature. Pediatric, temperature-sensitive, and operating room patients should be checked more frequently. Failure to monitor patient may result in skin damage or inappropriate patient temperature. PEDIATRICS - The temperatures of infants and children are more responsive to surface heating and cooling than adults. The smaller the patient, the more pronounced the effect because of the patient’s higher ratio of skin contact area to body mass. TEMPERATURE-SENSITIVE PATIENTS - Patients with impaired peripheral blood circulation caused by vascular diseases and patients who are incapacitated may be more sensitive to temperature changes than patients with more normal circulation. OPERATING ROOM PATIENTS - Patients with poor circulation associated with inadequate heart function, reduction in blood volume, and constriction of peripheral blood vessels may deviate from the normal response to the external application of heat and cold.

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1.0

SERVICE MANUAL Medi-Therm II

PATIENT SAFETY (continued)

WARNING •

Avoid placing additional heat sources between the patient and blanket. Skin damage can result. Heat applied by the blanket can result in a rise in skin temperature at the areas of contact. The additional heat rise due to electrosurgical currents flowing to the dispersive electrode could be sufficient to cause tissue injury. Each thermal effect by itself may be completely safe, but the additive effect may be injurious.1 Keep additional heat sources from between the patient and the blanket.

•

Prevent excessive and/or prolonged tissue pressure and shearing forces, especially over boney prominences. Skin damage may result. Localized skin injury due to tissue compressed between boney prominences and fluid-filled channels has occurred during prolonged cardiovascular procedures at blanket temperatures well below the scientifically established epidermal burn injury threshold.2 Local ischemia can follow the application of pressures exceeding capillary pressure resulting in tissue necrosis. This local effect may be enhanced by generalized impairment of the circulation, local shearing forces and increased metabolic demand because of temperature elevation. Pathological changes may begin in two (2) hours.

•

Keep the area between the patient and the blanket dry. Excessive moisture may result in skin damage. The application of heating or cooling may affect the toxicity of solutions. Prep solutions have been reported to injure the skin when allowed to remain between patients and water circulating heating blankets during prolonged procedures.3

CAUTION •

Place a dry absorbent sheet between the patient and the blanket when using all-vinyl blankets. A dry absorbent sheet placed between the patient and the Hyper/ Hypothermia Blanket will absorb perspiration. Vinyl blankets with nonwoven fabric surfaces do not require an absorbent sheet when using the nonwoven side toward the patient.

•

Federal law restricts this device to sale by or on the order of a physician.

REFERENCES

2

1

Gendron, F. G. Unexplained Patient Burns. chap. 5, p. 87, Quest Publishing Co., 1988.

2

Scott, Stewart M. Thermal Blanket Injury in the Operating Room. Arch. Surg., vol. 94, p. 181, Feb. 1967; Crino, Marjanne H. Thermal Burns Caused by Warming Blankets in the Operating Room. Clinical Workshop, vol. 29, pp. 149-150, Jan-Feb 1980; Gendron, Francis G. Journal of Clinical Engineering, vol. 5, no. 1, pp. 19-26, January-March 1980; Moritz, A. R. and Henriques, Jr., F.C. Studies of Thermal Injury II. The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns. Am. J. Path., 23:695, 1947; Stoll, Alice M. and Chianta, Maria A. Method and Rating System for Evaluation of Thermal Protection. Aerospace Medicine, vol. 40, no. 11, pp. 1232-1238, Nov. 1969; Stewart, T. P. and Magnano, S. Burns or Pressure Ulcers in the Surgical Patient. Decubitus, vol. 1, pp. 36-40, 1988.

3

Llorens, Alfred S. Reaction to povidone-iodine surgical scrub, scrub associated with radical pelvic operation. Am. J. Obstet. Gynecol., pp. 834-835, Nov. 14, 1974; Hodgkinson, Darryl J., Irons, George B. and Williams, Tiffany J., Chemical Burns and Skin Preparation Solutions. Surgery, Gynecology & Obstetrics, vol. 17 pp. 534-536, Oct. 1978.

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PATIENT SAFETY

2.0

MACHINE PRECAUTIONS

MACHINE PRECAUTIONS

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SERVICE MANUAL Medi-Therm II

DANGER Disconnect power before servicing unit. Risk of electric shock.

WARNING •

Repairs should be performed only by qualified personnel such as certified biomedical electronics technicians or certified clinical engineers familiar with repair practices for servicing medical devices, and in accordance with the Medi-Therm II Service Manual. Improper repair may result in death or serious injury, equipment damage, or malfunction.

•

Always perform the FUNCTIONAL CHECK AND SAFETY INSPECTION (section 7.3, p. 20) after making repairs and before returning the Medi-Therm II machine to patient use. Improper repair may result in death or serious injury, equipment damage, or malfunction.

•

Some manufacturer’s patient probes may contain compensation resistors in series with YSI400 series thermistors. Do not use these probes with the Medi-Therm II machine. Inaccurate patient temperature readouts will result and inappropriate therapy may be delivered. NOTE: Use YSI400 series patient probes or equivalent. (Refer to the list of recommended probes in section 5.0, p. 7 PROBE INFORMATION.)

•

Do not tip machine over without first draining the water out and unplugging the power cord. Electrical shock or damage to the machine can result.

CAUTION Add distilled water only. Failure to use distilled water may result in poor machine performance. •

Do not use alcohol, since it is flammable. Alcohol may also accelerate blanket deterioration.

•

Do not operate the machine without water, since damage to internal components may result.

•

Do not overfill. Overfilling may result in overflow because the water in the blanket drains back into the machine when the machine is turned off.

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3.0

REPAIR POLICY

SERVICE MANUAL Medi-Therm II The Medi-Therm II Hyper/Hypothermia machine is warranted free of defects in material and workmanship for a period of two (2) years, under the terms and conditions of the Gaymar warranty in place at the time of purchase. The compressor portion of the machine carries a five (5) year prorated warranty. The full warranty is available from Gaymar upon request. Medi-Therm II Hyper/ Hypothermia machines can be repaired at the factory or in the field. Upon customer request, a shipping carton will be provided to safely return the machine to Gaymar or a qualified Service Center. For customers who repair Gaymar Medi-Therm II machines at their location, this manual contains information to allow a qualified biomedical technician, familiar with practices for servicing medical devices, to make necessary repairs. Service training for the Hyper/Hypothermia machine is recommended and is available from Gaymar. For specific details, contact your Gaymar representative or the Technical Service Department at Gaymar. (See back cover of this manual for Gaymar telephone numbers.)

3.1

IN-WARRANTY REPAIRS

All in-warranty field repairs must be authorized by Gaymar’s Technical Service Department before proceeding.

3.2

OUT-OF-WARRANTY REPAIRS

The following repair options are available when local machine servicing is elected: I . Defective Component Replacement parts can be ordered. Specify the Gaymar part number; refer to Parts List in section 11, pp. 67 - 77 and 79 - 86 of this manual. 2. Defective Printed Circuit (PC) Board Defective PC boards can be exchanged for replacement boards at a fixed cost directly from the factory. 3. Defective Top Module The defective top module can be returned (without base) to the factory for repair. 4. Machine Repairs If the Medi-Therm II machine becomes defective and the cause of the problem cannot be determined, the complete machine can be returned to the factory for servicing at the purchaser’s expense. This normally represents the most expensive repair option. Please contact Gaymar to obtain an RG (returned goods) number prior to returning the machine.

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REPAIRS / WARRANTY

SPECIFICATIONS

4.0

SPECIFICATIONS

4.1

PHYSICAL SPECIFICATIONS

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SERVICE MANUAL Medi-Therm II

PHYSICAL SPECIFICATIONS MTA5942

MTA5900

MTA5901

37 in. high x 18-3/4 in. deep x 14 in. wide (94.0 cm high x 47.6 cm deep x 35.6 cm wide)

Dimensions

Weight

149 lb (full); 130 lb (empty); shipping wt, 164 lb (72.1 kg (full); 62.6 kg (empty); shipping wt, 74.4 kg

Normal Reservoir Operating Volume

Approximately 10 quarts (9-1/2 liters) distilled water

Operating Ambient Temperature Range

60°F to 90°F (15.6°C to 32.2°C)

60°F to 90°F (15.6°C to 32.2°C) 8.5 psi max (58.6 kPa max)

Dead Head Pressure 16 gph (gallons per hour) (60.6 liters/hour) *

Flow *

60°F to 80°F (15.6°C to 26.7°C)

16 gph (gallons per hour) (60.6 liters/hour) *

12 gph (gallons per hour) (45.4 liters/hour) *

* Minimum flow rates through a full size Gaymar Hyper/Hypothermia Blanket

4.2

THERMAL SPECIFICATIONS THERMAL SPECIFICATIONS

High Temperature Limits Fixed (S2) & (S3)

Low Temperature Limits Fixed (S1) Add Water Alert Actuation

MTA5942

MTA5900

MTA5901

111.2°F (44°C) to 120.2°F (49°C)

109.4°F (43°C) to 120.2°F (49°C)

109.4°F (43°C) to 120.2.°F (49°C)

(Machine will go into REMOVE FROM USE NOW / MACHINE SHUTDOWN condition and audible alarm will be on.) 26.6°F (-3.0°C) to 36.5°F (+2.5°C) (Machine will go into REMOVE FROM USE NOW / MACHINE SHUTDOWN condition and audible alarm will be on.) Less than 8 quarts (7.6 liters) of water in the cold reservoir

Check Probe Activation Temperature (whenever probe is used)

Below 89.6°F (32°C) or above 113°F (45°C)

Patient Temperature Control Range for Automatic Mode Blanket Water Temperature Control Range for Manual Mode

89.6°F (32°C) to 105.8°F (41°C)

39.2°F (4°C) to 107.6°F (42°C)

39.2°F (4°C) to 105.8°F (41°C)

39.2°F (4°C) to 105.8°F (41°C)

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4.2

SERVICE MANUAL Medi-Therm II

THERMAL SPECIFICATIONS (cont'd)

COOLDOWN RATE (typical)

45 40 35 30 25 20 15 10 5 0

Temperature (°C)

Temperature (°C)

WARM-UP RATE (typical)

0

5

10

15

20

25

45 40 35 30 25 20 15 10 5 0 0

Time (minutes)

10

15

20

25

Time (minutes)

Figure 1-Typical warm-up rate (with full size blanket)

4.3

5

Figure 2-Typical cooldown rate (with full size blanket)

ELECTRICAL SPECIFICATIONS

ELECTRICAL SPECIFICATIONS MTA5942 Patient Temperature Measurement Accuracy

MTA5900

MTA5901

±0.5°C, ±0.9°F (using Gaymar 400 series probe)

Display Accuracy

±0.3°C, ±0.5°F 1°C, 1°F

Blanket Water Temperature Display Resolution Patient Temperature

0.1°C, 0.1°F

Blanket Water Temperature

±0.8°C, ±1.4°F

Patient Temperature

±0.5°C, ±0.9°F

Controller Accuracy Chassis

100 microamps maximum

Patient Probe

50 microamps maximum

Current Leakage Input Voltage

120 ± 10 volts

120 ± 10 volts

100, +10, -5 volts

Frequency

60 Hz

60 Hz

50/60 Hz

1125 watts

1125 watts

1150 watts

with compressor and heater ON

11.5 amps

11.5 amps

13.0 amps

with compressor ON, heater OFF

8.5 amps

8.5 amps

8.8 amps

with heater ON, compressor OFF

5.0 amps

5.0 amps

6.0 amps

Power Consumption

Input Current

6

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SPECIFICATIONS

5.0

PROBE INFORMATION

PROBE INFORMATION

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SERVICE MANUAL Medi-Therm II Disposable Probes • DP400

Disposable Rectal/Esophageal Adult/Small Child (3' [0.9 meters] long, requires adaptor); YSI400 series type

Reusable Probes • PAT101

Patient probe-Rectal/Esophageal Adult (10' [3.0 meters] long); YSI400 series type

• PAT102

Patient probe-Rectal/Esophageal Pediatric (10' [3.0 meters] long); YSI400 series type

• PAT108

Patient probe-Skin surface (10' [3.0 meters] long); YSI400 series type

Probe Adaptor • ADP10

Reusable adaptor cable for DP400: connects Gaymar disposable probe to Gaymar or Cincinnati Sub-Zero control unit for all applications that call for Baxter/Pharmaseal No. 66N2700.

• ADP10B

Reusable adaptor cable for DP400: connects Gaymar disposable probe to American Medical Systems control unit or all applications that call for Baxter/Pharmaseal No. 66N27100.

WARNING Some manufacturer’s patient probes may contain compensation resistors in series with YSI400 series thermistors. Do not use these probes with the Medi-Therm II machine. Inaccurate patient temperature readouts will result and inappropriate therapy may be delivered. NOTE: Use YSI400 series patient probes or equivalent. (Refer to the list of recommended probes above.)

7

SERVICE MANUAL Medi-Therm II

control panel YSI 400 series or equivalent patient probe

connector hose

Hyper/Hypothermia blanket

Medi-Therm II machine

pinch clamp

alternate slide clamp

Clik-Tite® connector

Clik-Tite connectors and representative hose clamps

Quick-disconnects on machine end

Figure 3-Medi-Therm II System

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MEDI-THERM II SYSTEM

THEORY OF OPERATION

6.0

THEORY OF OPERATION, SYSTEM

The Gaymar Medi-Therm II machine provides a means of regulating patient temperature by supplying temperature-controlled water through a connector hose to a Gaymar Hyper/Hypothermia blanket. The blanket provides an interface for heating or cooling the patient. A patient probe senses patient temperature, which is displayed on the control panel. (See figure 3, p. 8.)

6.1

THEORY OF OPERATION, MEDI-THERM II MACHINE

The Medi-Therm II machine controls output water temperature by mixing hot and cold water from two reservoirs using hot and cold solenoid valves under microprocessor control. The feedback for control purposes is dependent on the machine’s operating mode. A circulating pump, heater and refrigeration unit (all under microprocessor control) are also utilized. Bimetallic thermostats and associated backup circuitry limit output water temperature independent of the microprocessor.

OPERATING MODES The Medi-Therm II machine may be operated in one of three operating modes: In MANUAL mode, the operator must observe patient temperature and manually adjust the blanket water set point temperature. An inline blanket water probe senses the temperature of the water pumped to the blanket and provides feedback for control purposes to the microprocessor. The patient temperature may be monitored by use of a patient probe. In AUTO mode, the operator sets the desired patient temperature. The patient’s temperature (as sensed by the patient probe) is automatically regulated to this set point. The patient probe input provides feedback to the microprocessor so it can adjust water temperature accordingly. In MONITOR mode, the operator can monitor patient temperature through the patient probe. No patient therapy is provided. The pump, heater, and hot and cold solenoid valves are de-energized.

WATER RESERVOIRS The hot water reservoir contains a small reserve of water. When the blanket water requires heating, a cartridge heater under microprocessor control quickly heats the water. The cold water reservoir maintains approximately 10 quarts (91/2 liters) of water at approximately 39.2°F (4°C). A cold water reservoir probe provides temperature feedback to the microprocessor which then cycles a refrigeration compressor to control the reservoir temperature.

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SERVICE MANUAL Medi-Therm II

6.1

THEORY OF OPERATION, MEDI-THERM II MACHINE (continued)

SERVICE MANUAL Medi-Therm II WATER TEMPERATURE CONTROL Hot and cold solenoid valves regulate the flow path by directing water returning from the blanket to either the hot or cold water reservoir. Regulating the flow path controls the temperature of water pumped to the blanket. The microprocessor controls solenoid valve operation. Only one valve may open at a time: When the HEAT status light is lit, the hot solenoid valve is open. Water returning from the blanket circulates through the hot water reservoir and is heated before being pumped back to the blanket. The heater, pump, and hot solenoid valve are energized. (See figure 10, p. 70.) When the COOL status light is lit, the cold solenoid valve is open. Water returns from the blanket to the cold water reservoir and is replenished by chilled water from the cold water reservoir before being pumped back to the blanket. The pump and cold solenoid valve are energized. (See figure 11, p. 70.) The refrigeration compressor maintains the cold water reservoir temperature and operates independently of the solenoid status. When the IN-TEMP status light is lit, either the blanket water temperature is within 1.8°F (1°C) of the setpoint (in MANUAL mode) or the patient temperature is within 1.8°F (1°C) of the setpoint (in AUTO mode). Water temperature is controlled by alternating between heating and cooling (See figures 10 and 11).

REFRIGERATION UNIT The refrigeration circuit (see figure 12, p. 71) consists of two heat exchangers operating at two pressures and two devices used to change these pressures. The first of these devices is the compressor which changes the gas pressure from low to high. The other device is the capillary tube which reduces the refrigerant pressure from high to low. Beginning the cycle at the capillary tube, high pressure liquid refrigerant flows in the capillary tube and is discharged into the evaporator coil. The evaporator coil, which is a heat exchanger, receives the refrigerant as a mixture of liquid and vapor at a pressure low enough so that it boils and absorbs heat from the water surrounding it. The heated refrigerant vapor then leaves the evaporator coils, enters the suction side of the compressor and is compressed, causing its pressure and temperature to increase. The vapor, much warmer than the ambient air, travels to the condenser. The condenser is the other heat exchanger. The condenser fan draws the colder ambient air over the condenser coils and removes the heat being carried by the refrigerant and causes it to condense back into liquid refrigerant. This completes the cycle and the high pressure liquid refrigerant is returned to the capillary tube to be used over again. The temperature of the water surrounding the evaporator coil (in the cold water reservoir) is controlled by the microprocessor. The microprocessor senses the temperature with a cold water reservoir probe and cycles the compressor relay on and off.

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THEORY OF OPERATION

6.1

THEORY OF OPERATION, MEDI-THERM II MACHINE (continued)

THEORY OF OPERATION

BACKUP SYSTEMS Backup systems within the Medi-Therm II machine limit the temperature of water exiting the machine to specified ranges in the event of a failure of the control system including the microprocessor: Maximum water temperature is limited by two bimetallic thermostats. If either of these two thermostats is actuated, a REMOVE FROM USE NOW / MACHINE SHUTDOWN circuit is triggered which: •

shuts down the pump and heater;

•

lights the ALERT and the REMOVE FROM USE NOW / MACHINE SHUTDOWN indicators; and,

•

sounds the audible alarm.

In addition, if the microprocessor is operational, the compressor shuts down, the displays blank, and the ALERT indicator and audible alarm turn on and off. Minimum water temperature is limited by a bimetallic thermostat. If this thermostat is actuated, a REMOVE FROM USE NOW / MACHINE SHUTDOWN circuit is triggered, which in turn:

6.2

SYSTEM COMPONENT INTERCONNECTIONS

•

shuts down the pump and heater;

•

lights the ALERT and the REMOVE FROM USE NOW / MACHINE SHUTDOWN indicators; and,

•

sounds the audible alarm. In addition, if the microprocessor is operational, the compressor shuts down, the displays blank, and the ALERT indicator and audible alarm turn on and off.

See figure 8, p. 67 for base-to-head and control/display board-to-power supply board connections; figure 18, p. 79 for system wiring diagram; figures 19, 20 and 21, pp. 80, 81, 82 for the electrical schematics; figures 22 and 23, pp. 83 and 84, for component layouts and part designations; and figure 24, p. 85 for the control/display board block diagram.

CONTROL/DISPLAY BOARD AND POWER SUPPLY BOARD The Medi-Therm II machine uses two printed circuit boards (see figure 8, p. 67): •

The control/display board contains the microprocessor circuits, the display circuits, and all other low voltage control circuits.

•

The power supply board contains the power supply, the low voltage to high voltage interface circuits, and the REMOVE FROM USE NOW / MACHINE SHUTDOWN backup safety circuits.

The control/display board connects to the patient probe jack J1 via P2 at J2 and to the digital control assembly panel via P4 at J4. All other connections from the system’s peripheral devices to the control/display board are made through the power supply board. A 26-pin cable connects the control/display board via P1 at J1 to the power supply board via P3 at J4.

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SERVICE MANUAL Medi-Therm II

6.2

6.3

SYSTEM COMPONENT INTERCONNECTIONS (continued)

POWER SUPPLY

SERVICE MANUAL Medi-Therm II Four cables connect the components in the base of the machine to the PC boards in the head (see figure 8, p.67): •

A 9-pin connector P6 ties the blanket water probe RT2, cold water reservoir probe RT1, flow switch S5, and level switch S4 to the power supply board at J2 and ultimately to the control/display board.

•

A 12-pin connector P7 ties the high voltage devices (pump, heater, hot solenoid valve SV2, cold solenoid valve SV1, and refrigeration compressor relay K1) to the interface circuits on the power supply board, as well as thermostats S1, S2, and S3 to the high voltage backup circuitry on the power supply board.

•

A 6-pin connector P5 connects transformer T1 housed in the base to the power supply circuitry at J3 on the power supply board.

•

A chassis ground harness from the control/display board connects to the chassis.

See figure 18, p.79 for the system wiring diagram; figures 19, 20 and 21, pp. 80, 81, 82 for the electrical schematics; figures 22 and 23, pp. 83, 84 for component layouts and part designations; and figure 24, p. 85 for the control/display board block diagram. Power enters the Medi-Therm II machine through circuit breaker CB1 to feed the refrigeration unit through relay K1. It also then enters the power supply board at J1 to feed the hot solenoid valve, cold solenoid valve, heater and pump triacs, the high voltage backup water temperature limiting circuits and transformer T1. Power to drive the low voltage circuits on the control/display board is derived from the machine’s power supplies which reside entirely on the power supply board. The transformer T1 output is rectified and filtered to generate unregulated positive and negative voltages. Q5, D1, L1 and associated components are configured as a DC to DC switching regulator in a buck configuration yielding a nominal output of +5.3 volts DC. Q6 is a linear regulator with a nominal output of plus twelve (+12) volts DC, while Q7, also a linear regulator, delivers a nominal output of minus twelve (-12) volts DC.

6.4

MACHINE FUNCTIONS

See figure 18, p. 79 for system wiring diagram; figures 19, 20 and 21, pp. 80, 81, 82 for the electrical schematics; figures 22 and 23, pp. 83, 84 for component layouts and part designations; and figure 24, p. 85 for the control/display board block diagram. The U37 microprocessor is fully dependent on the code stored in the U31 EPROM. When the machine is on, the microprocessor continually cycles through its main program loop to perform the following: • • • • • •

Thermistor output measurement (see section 6.4.1, p. 13) Digital control panel input (section 6.4.2, p. 13) Display update (section 6.4.3, p. 13) Peripheral input (section 6.4.4, p. 14) Blanket/Patient temperature control (section 6.4.5, p. 15) Cold water reservoir temperature control (section 6.4.6, p. 16)

Backup water temperature limiting is achieved independently of the microprocessor. (See section 6.4.7, p. 16.)

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THEORY OF OPERATION

6.4.1 THERMISTOR OUTPUT MEASUREMENT

THEORY OF OPERATION

Temperature measurement is achieved using 400 series thermistor beads located in the blanket water path (blanket water probe RT2), the cold water reservoir (cold water reservoir probe RT1), and in the patient via the patient probe jack J1. Under microprocessor U37 control, each of the three beads is connected to the current source circuitry (U38 and associated components) by a demultiplexor U49. At the same time, the resulting output voltage created by the current through the thermistor is presented to an amplifier circuit (U39 and associated components) via multiplexor U50. The amplified voltage is then applied to a voltage-to-frequency converter U24. A frequency up to 100kHz is presented to port pin P3.5 of the microprocessor. The microprocessor converts the incoming frequency to a temperature value. At regular intervals two compensation resistors R13 and R12 are also processed in the same manner. These compensation resistors are precision resistors with values at each end of the probe temperature range of 32°F (0°C) to 122°F (50°C). The values from the precision resistors are used to compensate for circuit drift.

6.4.2 DIGITAL CONTROL PANEL INPUT

User input is entered via a digital control panel. The input from the buttons is decoded by U45. The “data available” line of U45 is tied to the microprocessor port pin P3.3. When a button press is decoded and debounced by U45, the “data available” line goes high and the microprocessor responds by inputting the decoded value.

6.4.3 DISPLAY UPDATE

For display of measured and set point temperatures, 7 segment LED displays are utilized: •

The set point display is driven by driver chip U48. The microprocessor interfaces to it via the data bus at addresses 0FFF8H, 0FFF9H, 0FFFAH, 0FFFBH.

•

The patient display is driven by driver chip U6. The microprocessor interfaces to it via the data bus at addresses 0FFF4H, 0FFF5H, 0FFF6H, 0FFF7H.

•

The blanket display is driven by driver chip U5. The microprocessor interfaces to it via the data bus at addresses 0FFECH, 0FFEDH, 0FFEEH, 0FFEFH.

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SERVICE MANUAL Medi-Therm II

6.4.3 DISPLAY UPDATE (continued)

SERVICE MANUAL Medi-Therm II All alarm and status indicators are lit by LED bars driven by inverter/driver IC’s: •

The alarm latch U53 is the interface between the microprocessor and the ALERT, ADD WATER, CHECK PROBE, CHECK FLOW, REMOVE FROM USE NOW / MACHINE SHUTDOWN, SELECT, °F* and °C drivers via the data bus at address 0FFBFH. A high signal written to the latch by the microprocessor activates the individual inverter/ drivers to light the corresponding indicator.

•

The mode display latch U54 is the interface between microprocessor and the IN-TEMP, COOL, HEAT, FLOW-OK, AUTO, MANUAL, and MONITOR drivers via the data bus at address 0FFDFH. A high signal written to the latch by the microprocessor activates the individual inverter/drivers.

•

The control latch U51 is the interface between the microprocessor and the two leader light drivers via the data bus at address 0FF7FH. When this latch is selected, a low signal on the data line from the microprocessor causes a high signal on the latch output Therefore, these two LED bar displays are “active low” in the eyes of the microprocessor in contrast to all the other LED bar displays of the machine.

The audible alarm is driven either by a high signal from the control latch U51 (from the microprocessor via the data bus at address 0FF7FH) or a high RFU IN signal from Q10 on the power supply board. A low data line signal from the microprocessor to U51 causes a high signal on the latch output Therefore, the alarm is “active low” in the eyes of the microprocessor. NOR gate U40, driver U26 and transistor Q1 work in conjunction to activate the alarm.

6.4.4 PERIPHERAL INPUT

The input buffer U55 is the interface between the microprocessor (via the data bus at a “read” address of 0FFFEH) and the input signals from the flow switch S5 and the level switch S4 (which travel from the base through the power supply board), the probe presence switch within the patient probe jack J1, and the service mode button S3 on the control/display board. The lines to the buffer from the peripheral devices are default high (via pull-up resistors). The level switch S4 will pull its buffer input line low when it senses a sufficient water level. The flow switch S5 will pull its buffer input line low when it senses sufficient flow. The probe presence switch within J1 will pull its buffer input line low when it senses the presence of the patient probe. Pressing the service mode switch S3 on the control/display board will pull its buffer input line low.

*

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Some models do not have the °C/°F feature.

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THEORY OF OPERATION

6.4.5 BLANKET / PATIENT TEMPERATURE CONTROL

THEORY OF OPERATION

If the machine is in MANUAL mode, the blanket water temperature as sensed by the blanket water probe is used as the feedback signal for controlling the water temperature to the MANUAL mode set point temperature. If the machine is in AUTO mode, the patient temperature as sensed by the patient probe connected to the patient probe jack is used as the feedback signal for controlling the patient temperature to the AUTO mode set point temperature. The machine accomplishes this by adjusting the water temperature. For water temperature control, the microprocessor control system outputs a pulse train to each solenoid valve. The pulse train to the hot solenoid (and also heater) is the complement of the pulse train to the cold solenoid. The pulse train duty cycle depends on the magnitude and sense of the control signal calculated by the microprocessor. That is, while the solenoids are each either on or off, the ratio of on time to off time is proportional to the calculated control signal amplitude. For large differences between set point and probe temperatures, the output to each solenoid valve will be either on or off. For differences approaching zero, the outputs to the solenoid valves (and heater) will switch on and off, with the on and off times automatically adjusted to maintain a probe temperature equal to the set point. The circulating pump is energized whenever the unit is in AUTO or MANUAL modes. The control latch U51 on the control/display board is the interface between the microprocessor (via the data bus at address 0FF7FH) and the peripheral drivers on the power supply board. Interface circuitry on the power supply board consists of U1, U2, U7, U8, Q3, Q4, Q8, Q9, and associated components. U1, U2, U7, and U8 are optically coupled triac drivers used to control their respective triacs (Q3, Q4, Q8, and Q9); these combinations provide electrical isolation between the low voltage microprocessor control circuits and the line voltage circuits. The heater, pump, hot solenoid valve, and cold solenoid valve are individually controlled by the microprocessor through latch U51 on the control/display board. A high signal on the data line from the microprocessor causes a low signal on the appropriate output line of U51 which then sinks current from the power supply board to activate the peripheral devices. Pin 11 of U51 on the control/display board and U8 and Q9 of the power supply board control the cold solenoid valve while pin 9 of U51 on the control/display board and U7 and Q8 of the power supply board control the hot solenoid valve. Pin 8 of U51 on the control/display board and U2 and Q4 of the power supply board control the circulating pump. Pin 7 of U51 on the control/display board and U1 and Q3 of the power supply board control power to the heater.

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SERVICE MANUAL Medi-Therm II

SERVICE MANUAL Medi-Therm II

6.4.6 COLD WATER RESERVOIR TEMPERATURE CONTROL

The control latch U51 on the control/display board is the interface between the microprocessor (via the data bus at address 0FF7FH) and the refrigeration compressor relay driver on the power supply board. A high signal on the appropriate data line causes a low signal at pin 6 of U51 on the control/display board, which then activates Q12 on the power supply board. Q12 on the power supply board is the interface between the control/display board and the coil of the power relay K1 located in the machine base. The microprocessor switches power through the relay to the refrigeration compressor at cut-out and cut-in temperatures of 38°F (3.3°C) and 42.5°F (5.8°C). These temperatures are sensed by the cold water reservoir probe RTl located in the water reservoir. (See figure 12, p. 71.) Control of the cold water reservoir temperature takes place whenever the machine is on.

6.4.7 BACK-UP WATER TEMPERATURE LIMITING

The power supply board includes the REMOVE FROM USE NOW / MACHINE SHUTDOWN circuitry, which includes U3, U4, U5, U6, U9, U10, D2, D3, Q1, Q2, their interconnected components, and fixed, nonadjustable thermostats S2, S3, and S1 located in the base. Under normal circumstances, Q1 and Q2 are kept turned on by the action of R7, C10, and D4 and R5, C15, and D5 to complete the conduction path for the heater and pump. If the blanket water falls into the low temperature limit range, S1 will open. If the blanket temperature rises into the high temperature limits ranges, S2 and/or S3 will open. (See section 4.2 Thermal Specification table, page 5, for the correct high or low temperature limits with corresponding model number of your machine.) When any one of these thermostats opens, it directly interrupts the circuit and shuts off the pump and heater; at the same time, full line voltage will appear between J1-2 and J1-3. In this case, U5 and U10 will be turned on by the action of R4, D3, and associated parts while U3 and U9 will be turned on by the action of R6, D2, and associated parts. U5 prevents Q2 from turning on and U3 prevents Q1 from turning on even if the open thermostat(s) closes again. The output of either U9 or U10, through buffer Q10, signals the microprocessor that a thermostat has tripped and that a REMOVE FROM USE NOW / MACHINE SHUTDOWN condition has resulted. Thus, should any thermostat (S1, S2, or S3) trip, the heater and pump are shut off and the microprocessor is notified. On the control/display board, a high signal from Q10 of the power supply board feeds NOR gate U40 to drive the audible alarm, feeds driver U52 to light the REMOVE FROM USE NOW / MACHINE SHUTDOWN LED, and feeds driver U11 to light the ALERT LED. All this is done independent of the microprocessor. This same signal is sent to port pin P3.2 of the microprocessor through C1, R1, and driver U11. If the microprocessor is operational at the event of a high signal from Q10 of the power supply board, the signal at P3.2 causes the microprocessor to shut off the 7 segment displays, flash the ALERT LED and light the REMOVE FROM USE NOW / MACHINE SHUTDOWN LED, toggle the audible alarm, store the appropriate RFU* code indicating the reason for the shutdown, turn off the heater and pump triacs Q3 and Q4, turn off the solenoid triacs Q8 and Q9, and turn off the compressor transistor Q12. Anytime the microprocessor

* RFU = REMOVE FROM USE NOW / MACHINE SHUTDOWN

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THEORY OF OPERATION

6.4.7 BACK-UP WATER TEMPERATURE LIMITING (continued)

THEORY OF OPERATION

goes into a shutdown condition it also sends an output signal from port pin P3.4, through U40 of the control/display board, to command, via Q11, U4, and U6 on the power supply board, a REMOVE FROM USE NOW / MACHINE SHUTDOWN condition. The process of turning off the heater and pump triacs Q3 and Q4 by the microprocessor removes power from the REMOVE FROM USE NOW / MACHINE SHUTDOWN circuitry on the power supply board which then allows the indicators on the control/display board to toggle under microprocessor control. This shutdown condition by the microprocessor program will remain until the machine is powered down. If, upon machine turn on, the fault condition still exists, attempting to resume therapy (which would turn on the pump and possibly heater) will replace power to the REMOVE FROM USE NOW / MACHINE SHUTDOWN circuits on the power supply board and cause the REMOVE FROM USE NOW / MACHINE SHUTDOWN condition to recur. Also, if during normal operation, the microprocessor senses internal problems, it will attempt a shutdown as described above. (See table 2, section 8.1, p. 35.) If the microprocessor is nonoperational at the event of a signal from Q10 of the power supply board, the user is notified of the REMOVE FROM USE NOW / MACHINE SHUTDOWN condition by the fact that the above mentioned indicators are on continuously. In addition, there are separate, redundant circuits on the power supply board, each triggered by any of the thermostats, that insure that the pump and heater remain off even if the thermostat cools sufficiently to close again. The REMOVE FROM USE NOW / MACHINE SHUTDOWN condition remains latched and can be cleared only by an operator intervention in the form of turning the machine circuit breaker off. If, upon machine turn on, the fault condition still exists, attempting to resume therapy will cause the REMOVE FROM USE NOW / MACHINE SHUTDOWN condition to recur.

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SERVICE MANUAL Medi-Therm II