MEDI-THERM III Service Manual Rev A Oct 2008

SERVICE MANUAL Medi-Therm® III

Before you begin . . .

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 MediTherm® III Service Manual.

•

Always perform the FUNCTIONAL CHECK AND SAFETY INSPECTION (section 7.3, p. 20) after making repairs and before returning the Medi‑Therm III machine to patient use.

CAUTION

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

Improper repair may result in death or serious injury, equipment damage, or malfunction.

RECEIVING INSPECTION Upon receipt, unpack the Medi-Therm III machine. Save all packing material. Perform a visual and mechanical inspection for concealed damage by removing the wraparound from the chassis (see page 75). If any damage is found, notify the carrier at once and ask for a written inspection. Photograph any damage and prepare a written record. Failure to do this within 15 days may result in loss of claim. Refer to section 7.0 of this Medi-Therm III Service Manual for additional details.

OPERATING INSTRUCTIONS For information on operating the Medi-Therm III machine, refer to the Medi-Therm III Operator's Manual.

Medi-Therm and Clik-Tite are registered trademarks of Gaymar Industries, Inc. ©2000. Gaymar Industries, Inc. All rights reserved. www.gaymar.com

Do not return the Medi-Therm III machine to Gaymar Industries without first contacting Gaymar's Technical Service Department for assistance. Telephone:

Direct Toll Free

(716) 662-2551 1 800 828-7341

IMPORTANT Before operating the Medi-Therm III machine, remove the compressor shipping braces. See p. 88, figure B.

SERVICE MANUAL Medi-Therm® III

Section

CONTENTS

Description

CONTENTS

Page

1.0 PATIENT SAFETY... 1 2.0 MACHINE PRECAUTIONS... 3 3.0 REPAIR POLICY... 4 3.1 In-Warranty Repairs... 4 3.2 Out-of-Warranty Repairs... 4 4.0 SPECIFICATIONS... 5 4.1 Physical Specifications... 5 4.2 Thermal Specifications... 5 4.3 Electrical Specifications... 6 5.0 PROBE INFORMATION... 7 6.0 THEORY OF OPERATIONS... 9 6.1 Machine... 9 6.2 Interconnections... 11 6.3 Power Supply... 12 6.4 Machine Functions... 12 7.0 FUNCTIONAL CHECK, SAFETY INSPECTION, PREVENTIVE MAINTENANCE... 18 7.1 Receiving Inspection... 18 7.2 Cleaning Procedures... 18 7.3 Functional Check and Safety Inspection... 20 7.4 Inspection Form... 33 8.0 TROUBLESHOOTING & SERVICE MODES... 34 8.1 Service Modes... 34 8.2 Troubleshooting Charts... 38 9.0 REPAIR PROCEDURES... 57 9.1 Refrigeration System... 57 9.2 Replacing the Power Supply Board... 59 9.3 Replacing the Control/Display Board... 60 9.4 Replacing the Top Cover... 61 9.5 Replacing Thermostats... 62 9.6 Cleaning the Flow Switch... 63 9.7 Replacement Parts... 64 9.8 Shipping/Repacking Instructions... 64 10.0 REFERENCE TABLES... 65 10.1 Celsius-Fahrenheit Conversion... 65 10.2 Temperature vs. Resistance... 66 11.0 SERVICE INFORMATION... 67

Table 1 2 3 4 5 6A 6B 7 8 9 10

Description

TABLES

Page

High Temperature Limits... 25 RFU Error Codes... 35 Service Modes... 36 Celsius/Fahrenheit Conversion... 65 Temperature vs. Resistance... 66 Operator Controls/Indicators... 68 Operator Controls/Indicators... 71 Parts List (base)... 77 Parts List (head)... 78 Control/Display Board Parts List... 85 Power Supply Board Parts List... 86

i

SERVICE MANUAL Medi-Therm® III

FIGURES

ii

ILLUSTRATIONS

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 9A 9B 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Typical Warm-up Rate...6 Typical Cooldown Rate...6 Medi-Therm III 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 Operator Controls/Indicators...70 Heating Flow Diagram...72 Cooling Flow Diagram...72 Refrigeration Flow Diagram...73 Test Setup...74 Machine Disassembly...75 Parts Diagram (base)...76 Parts Diagram (head)...78 Thermostat Wiring Diagram . ...79 System Wiring Diagram...81 Power Supply Board Schematic (sheet 1 of 3)...82 Control/Display Board Schematic (sheet 2 of 3)...83 Control/Display Board Schematic (sheet 3 of 3)...84 Control/Display Board...85 Power Supply Board...86 System Block Diagram...87 Shipping/Repackaging Instructions...88

SERVICE MANUAL Medi-Therm® III 1.0

PATIENT SAFETY

PATIENT SAFETY

Use the Medi-Therm III 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 III 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 III 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 III 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 use of equipment. Check the integrity of the skin according to department protocol when regulating temperature with external devices. Frequency of assessment and documentation will vary depending upon the individual response of the patient. Failure to monitor patient may result in skin damage or inappropriate patient temperature. PEDIATRICS-The core temperature of infants and children is 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.

1

SERVICE MANUAL Medi-Therm® III

PATIENT SAFETY

1.0

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 tem‑ perature 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 Hy‑ per/Hypothermia Blanket will absorb perspiration. Vinyl blan‑ kets with nonwoven fabric surfaces do not require an absor‑ bent 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, JanFeb 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. Ob‑ stet. 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.

SERVICE MANUAL Medi-Therm® III

MACHINE PRECAUTIONS

2.0 MACHINE PRECAUTIONS

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 MediTherm III 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 III 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 YSI 400 series thermistors. Do not use these probes with the MediTherm III machine. Inaccurate patient temperature readouts will result and inappropriate therapy may be delivered. NOTE: Use YSI 400 series patient probes or equivalent. (Refer to the list of recommended probes in section 5.0, p. 7 PROBE INFORMATION.)

•

All wire-lead, patient-connected transducer assemblies are subject to reading error, local heating, and possible damage from high-intensity sources of RF energy. Inadequately grounded electrosurgical equipment represents one such source, since capacitively-coupled currents may seek alternate paths to ground through probe cables and associated instruments. Patient burns may result. If possible, remove the probe from patient contact before activating the surgical unit or other RF source. If probes must be used simultaneously with electrosurgical apparatus, hazards can be reduced by selecting a temperature monitoring point which is remote from the expected RF current path to the ground return pad.

•

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. Overfilling may also result in splashing from the overflow tube during transport.

3

REPAIRS / WARRANTY

3.0

REPAIR POLICY

SERVICE MANUAL Medi-Therm® III The Medi-Therm III 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 III 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 III 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 the Parts Lists in section 11, pp. 76–88 of this manual. 2. Machine Repairs If the Medi-Therm III 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.

4

SERVICE MANUAL Medi-Therm® III

SPECIFICATIONS

4.0

SPECIFICATIONS

4.1

PHYSICAL SPECIFICATIONS MTA6900

MTA6901 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

141 lb (full); 121 lb (empty); shipping wt,136 lb 64.0 kg (full); 54.9 kg (empty); shipping wt, 61.7 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)

Dead Head Pressure

9.0 psi max (62 kPa max)

Flow *

16 gph [gallons per hour] 60.6 liters/hour) *

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

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

4.2

THERMAL SPECIFICATIONS 111.2°F (44°C) to 120.2°F (49°C)

High Temperature Limits Fixed (S2) & (S3)

(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)

Low Temperature Limits Fixed (S1)

Add Water Alert Actuation

(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 Water Flow Alert Actuation

6 GPH

Check Probe Activation Temperature (whenever probe is used)

Below 84.2°F (29°C) or above 113°F (45°C)

Patient Temperature Control Range for Automatic Mode

86.0°F (30°C) to 105.8°F (41°C)

Blanket Water Temperature Control Range for Manual Mode

39.2°F (4°C) to 107.6°F (42°C)

5

SERVICE MANUAL Medi-Therm® III

SPECIFICATIONS

4.2

THERMAL SPECIFICATIONS (cont'd)

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

4.3

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

ELECTRICAL SPECIFICATIONS MTA6900

Patient Temperature Measurement Accuracy

MTA6901

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

Display Accuracy

±0.3°C, ±0.5°F Blanket Water Temperature

1°C, 1° F

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

120V ± 10V

100V +10V, -5 V

Frequency

60 Hz

50/60 Hz

Input Current

11.5A

13.0 A

Regulatory

UL416 CSA C22.2 No. 125

Electromagnetic Compatibility

6

Meets EN60601-1-2:1993 (CISPR 11 Classified as Class A, Group 1 ISM Equipment)

SERVICE MANUAL Medi-Therm® III 5.0

PROBE INFORMATION

PROBE INFORMATION

Disposable Probes • DP400CE Disposable Rectal/Esophageal Adult/Small Child (3' [0.9 meters] long, requires adaptor); YSI 400 series type

Probe Adaptor • ADP10CE Reusable adaptor cable for DP400: connects Gaymar disposable probe to Gaymar or Cincinnati Sub-Zero control unit. Reusable Probes • PAT101

Patient probe-Rectal/Esophageal Adult (10' [3.0 meters] long); YSI 400CE series type

• PAT102

Patient probe-Rectal/Esophageal Pediatric (10' [3.0 meters] long); YSI 400 series type

• PAT108

Patient probe-Skin surface (10' [3.0 meters] long); YSI 400 series type

WARNING Some manufacturer’s patient probes may contain compensation resistors in series with YSI 400 series thermistors. Do not use these probes with the Medi-Therm III machine. Inaccurate patient temperature readouts will result and inappropriate therapy may be delivered. NOTE: Use YSI 400 series patient probes or equivalent. (Refer to the list of recommended probes above.)

7

SERVICE MANUAL Medi-Therm® III

MEDI-THERM® III SYSTEM

Figure 3-Medi-Therm III System

8

SERVICE MANUAL Medi-Therm® III 6.0

THEORY OF OPERATION, SYSTEM

THEORY OF OPERATION The Gaymar Medi-Therm III 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.) The Medi-Therm III machine controls output water temperature by mixing hot and cold water using hot and cold solenoid valves under microcontroller control. A circulating pump, heater and refrigeration unit are also utilized. Bimetallic thermostats and associated backup circuitry limit output water temperature independent of the microcontroller. The feedback for control purposes depends upon the machine's operating mode. The Medi-Therm III machine may be operated in one of three operating modes: • In MANUAL mode, the operator sets the desired blanket temperature. A temperature sensor within the machine monitors the water temperature and the machine heats or cools the water as required to bring the blanket to the SET POINT temperature. The patient temperature may be monitored by use of a patient probe connected to the patient probe jack on the front of the unit. • In AUTO mode, the Medi-Therm III machine automatically regulates the patient's temperature to the selected SET POINT. The machine constantly compares actual patient temperature with the SET POINT value, and automatically adjusts the blanket temperature so that the desired patient temperature is achieved. • In MONITOR mode, the operator can monitor patient temperature through the patient probe, without providing therapy. Hyperthermia/hypothermia blankets may be placed either under or over the patient, depending upon the type of procedure. Some applications may require a second blanket in order to achieve additional or more rapid heating or cooling. For these situations, a second blanket may be connected to the Medi‑Therm III machine. The rate of patient heating or cooling may also be increased by positioning half- and full-sized blankets so that greater body surface is in contact with the blankets.

6.1

THEORY, MEDI-THERM III MACHINE

Whenever the machine is on, 10 quarts of water are maintained cold in the cold water reservoir. A cold water reservoir probe provides temperature feedback to the microcontroller which cycles the refrigeration unit on at 42.5°F (5.8°C) and off at 38.0°F (3.3°C). When the blanket water requires cooling, water is pumped from the cold water reservoir. When the blanket water requires heating, a cartridge heater is used to quickly heat the water.

9

SERVICE MANUAL Medi-Therm® III

THEORY OF OPERATION 6.1

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

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 microcontroller 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 fig. 10, p. 72.) 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 fig. 11, p. 72.) The refrigeration unit 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 10–11) with the heater cycled on and off as needed.

REFRIGERATION UNIT

The refrigeration circuit (see figure 12, p. 73) 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 microcontroller. The microcontroller senses the temperature with a cold water reservoir probe and cycles the compressor relay on and off.

10

SERVICE MANUAL Medi-Therm® III 6.1

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

THEORY OF OPERATION BACKUP SYSTEMS

Backup systems within the Medi-Therm III machine limit the temperature of water exiting the machine to specified ranges in the event of a failure of the control system including the microcontroller: 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 microcontroller 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 microcontroller 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. 81 for system wiring diagram; figures 19–21, pp. 82–84 for electrical schematics; figures 22–23, pp. 85–86 for component layouts and part designations; and figure 24, p. 87 for the system block diagram.

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

The control/display board contains the microcontroller 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.

11

SERVICE MANUAL Medi-Therm® III

THEORY OF OPERATION 6.2

SYSTEM COMPONENT INTERCONNECTIONS (continued)

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.

6.3

POWER SUPPLY

See figure 18, p.81 for the system wiring diagram; figures 19–21, pp. 82–84 for the electrical schematics; figures 22–23, pp. 85–86 for component layouts and part designations; and figure 24, p. 87 for the system block diagram. Power enters the Medi-Therm III 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. 81 for system wiring diagram; figures 19–21, pp. 82–84 for the electrical schematics; figures 22–23, pp. 85–86 for component layouts and part designations; and figure 24, p. 87 for the system block diagram. The U37 microcontroller is fully dependent on the code stored in the U31 EPROM. When the machine is on, the microcontroller 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 microcontroller. (See section 6.4.7, p. 16.)

12

SERVICE MANUAL Medi-Therm® III 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 microcontroller 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 microcontroller. The microcontroller 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 microcontroller port pin P3.3. When a button press is decoded and debounced by U45, the “data available” line goes high and the microcontroller 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 microcontroller interfaces to it via the data bus at addresses 0FFF8H, 0FFF9H, 0FFFAH, 0FFFBH. • The patient display is driven by driver chip U6. The microcontroller interfaces to it via the data bus at addresses 0FFF4H, 0FFF5H, 0FFF6H, 0FFF7H. • The blanket display is driven by driver chip U5. The microcontroller interfaces to it via the data bus at addresses 0FFECH, 0FFEDH, 0FFEEH, 0FFEFH.

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SERVICE MANUAL Medi-Therm® III

THEORY OF OPERATION 6.4.3 DISPLAY UPDATE (continued)

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 microcontroller 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 microcontroller activates the individual inverter/drivers to light the corresponding indicator.

•

The mode display latch U54 is the interface between the microcontroller 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 microcontroller activates the individual inverter/drivers.

•

The control option display latch U64 is the interface between the microcontroller and the GRADUAL, MODERATE, and RAPID drivers via the databus at address FDFFH. A high signal written to the latch by the microcontroller activates the individual drivers.

•

The control latch U51 is the interface between the microcontroller 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 microcontroller causes a high signal on the latch output Therefore, these two LED bar displays are “active low” in the eyes of the microcontroller 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 microcontroller 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 microcontroller to U51 causes a high signal on the latch output. Therefore, the alarm is “active low” in the eyes of the microcontroller. Transistor Q2 activates the alarm.

6.4.4 PERIPHERAL INPUT

The input buffer U55 is the interface between the microcontroller (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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SERVICE MANUAL Medi-Therm® III 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. When cooling is required, the water temperature the machine uses in AUTO mode is dependent on the CONTROL OPTION setting selected: RAPID-the coldest water is used for cooling and the water temperature used can be as low as 4°C. MODERATE-cooling water temperature is limited to 15°C (27°F) below the patient temperature. GRADUAL-cooling water is limited to 10°C (18°F) below the patient temperature. For water temperature control, the microcontroller outputs a pulse train to each solenoid valve and the heater. The pulse train duty cycle depends on the magnitude and sense of the control signal calculated by the microcontroller. That is, while the solenoids and heater are 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 the cold solenoid will be on and the output to the hot solenoid/heater combination will be off, or vice-versa. For differences approaching zero, the output pulse train will be applied to the hot solenoid and cold solenoid in a complementary fashion, with the on times and off times automatically adjusted to maintain a probe temperature equal to the set point, or the output pulse train will be applied to the heater (with the hot solenoid remaining open), with the on times and off times of the heater 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 microcontroller (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 microcontroller control circuits and the line voltage circuits. The heater, pump, hot solenoid valve, and cold solenoid valve are individually controlled by the microcontroller through latch U51 on the control/display board. A high signal on the data line from the microcontroller 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.

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THEORY OF OPERATION

SERVICE MANUAL Medi-Therm® III 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.

6.4.6 COLD WATER RESERVOIR TEMPERATURE CONTROL

The control latch U51 on the control/display board is the interface between the microcontroller (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 microcontroller 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. 73.) 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 microcontroller 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 microcontroller is notified. On the control/display board, a high signal from Q10 of the power supply board feeds Q2 to drive the audible alarm, feeds driver U62 to light the REMOVE FROM USE NOW / MACHINE SHUTDOWN LED, and feeds driver U60 to light the ALERT LED. All this is done independent of the microcontroller. This same signal is sent to port pin P3.2 of the microcontroller Q3. If the microcontroller is operational at the event of a high signal from Q10 of the power supply board, the signal at P3.2 causes the microcontroller 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 microcontroller

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