System 2000 Service Manual

© 1998 CONMED Corporation 310 Broad Street Utica, New York 13501 U.S.A.

For Technical Service or Return Authorization Phone: 303-699-7600 / 1-800-552-0138 Extension 5274 Fax 303-699-1628 For Customer Service or to order parts phone: 1-800-448-6506 / 315-797-8375 / Fax 315-735-6235 or contact your CONMED Representative. European Authorized Representative MDSS GmbH Burckhardtstr 1 D - 30163 Hannover Germany The revision level of this manual is specified by the highest revision letter found on either the inside front cover or enclosed errata pages (if any). Effective use of this Service Manual depends on the user having ready access to the Hyfrecator® 2000 Operator’s Manual, Cat No. 7-900-OM-ENG, available separately from Conmed Corporation Customer Service.

Manual Number 7-900-SM-ENG Rev. -

2000 Table of Contents Section

Title

Page

1.0 1.1 1.2 1.3 1.4 2.0 2.1 2.1.1 2.2 2.3 2.4 2.5 3.0 3.1 3.2 3.2.1 3.2.1.1 3.2.1.2 3.2.1.3 3.2.1.4 3.2.2 3.2.2.1 3.2.2.2 3.2.2.3 3.2.3 3.2.4 3.3 3.3.1 3.3.2 3.3.2.1 3.3.2.2 3.3.2.3 3.3.2.4 3.3.2.5 3.3.2.6 3.3.2.7 3.3.3 3.3.4 3.3.4.1 3.3.4.1.1 3.3.4.1.2 3.3.4.1.3

GENERAL INFORMATION...1 Foreword ...1 Intended use...1 Warranty ...2 Factory Service...2 PRODUCT DESCRIPTION...3 Controls, Displays & Connectors...3 Power Setting Storage...4 Specifications...4 Service Precautions...5 Mains Voltage Strapping...7 Environmental Protection...7 THEORY OF OPERATION...8 Overview ...8 A2 Power PWB...8 Power Supplies...8 Mains & Isolation...8 Low Voltage Supplies...9 Pre-Regulated High Voltage (PRHV) Supply...9 High Voltage Switching Regulator...9 RF Generation...10 RF Gate Drive & Monitor...10 RF Power Amplifier (PA)...10 Patient Circuits...10 Isolated Switch Detector...10 Tone Generator and Monitor...11 A1 Display/Control PWB...11 Dual-Channel Architecture...12 A1 Signal Descriptions...13 Mnemonic Conventions...13 Signal Levels...13 DC Power Signals...13 External Input Signals...13 External Output Signals...13 On-Board I/O Signals...14 Control/Monitor Communication...14 Power-Up Behavior...14 Operating Modes...14 Run Mode...15 Output Mode Selection...15 Power Display...15 PSET Transfer...16

2000 Section

Title

Page

3.3.4.1.4 3.3.4.1.5 3.3.4.1.6 3.3.4.1.7 3.3.4.1.8 3.3.4.1.9 3.3.4.2 3.3.4.2.1 3.3.4.2.2 3.3.4.2.3 3.3.4.2.4 3.3.5 3.3.5.1 3.3.5.2 3.3.5.3 4.0 4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6 4.2.7 4.3 4.3.1 4.3.2 4.3.3 4.4 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7 4.4.7.1 4.4.7.2 4.4.7.3 4.4.7.4 4.4.7.5 4.4.7.6 4.4.7.7 4.4.7.8 4.4.7.9 4.4.8 4.4.8.1 4.4.8.2

Power Adjustment...16 Setting Storage...16 Activation...17 Gate Waveform Generation...18 HV Voltage Control...18 Tone Generation...18 Service Mode...18 Service Mode Entry...18 Service Calibrate Mode...20 Service Pseudo-Run Mode...22 Service Last Fault Recovery Mode...23 Control/Monitor Interaction...23 Fault Detection Protocol...23 Fault Code Generation...23 Power On Self Test (POST)...24 MAINTENANCE...25 General Maintenance Information...25 Preventative Maintenance...25 Physical Inspection and Cleaning...25 DC Isolation Tests...26 Functional Testing...26 Mains Frequency Leakage...27 RF Output Power Testing...28 RF Leakage Test...29 Return to Service...31 Recalibration of RF Output Power...32 Service Mode Entry...32 RF Output Adjustment...32 Calibration Verification...34 Troubleshooting and Repair...34 Using Fault Codes...35 User Error and Accessory Faults...35 Interpreting Faults During POST...35 Using Pseudo-Run Mode...36 Using Recalibration...36 Fault Isolation Techniques...36 A1 Control/Display PWB Problems...38 Verifying Microcontroller Faults...38 Gate Waveform Problems...39 VGATE Problems...40 VCON Problems...40 Display Problems...40 Mode Setting Problems...41 Encoder Problems...42 Accessory Push-Button Problems...43 EEPROM Problems...43 A2 Power PWB Problems...44 Mains Power Problems...44 Low Voltage DC Power Problems...45

2000 Section

Title

Page

4.4.8.3 4.4.8.4 4.4.8.5 4.4.8.6 5.0 5.1 5.1.1 5.1.1.1 5.1.1.2 5.1.1.3 5.1.2 5.1.2.1 5.1.2.2 5.1.3 5.1.4 5.1.4.1 5.2 Appendix

HV Supply Problems...45 Switch Isolator Problems...47 RF Output Problems...47 Tone Generator Problems...48 TECHNICAL DATA...49 General ...49 Disassembly and Reassembly...49 Front Panel...51 Rear Enclosure...51 Connector Plate...52 Component Replacement...52 A1 PWB Components...52 A2 PWB Components...53 Parts Ordering Information...55 Waveforms...55 RF Output...55 Schematics, Assembly Drawings and Parts Lists...55 Fault Codes...A-1

Figure

Title

3.1 3.2 3.3 4.1 4.2 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8

Service Mode Menu Diagram...19 Effects of Offset & Gain Adjustments...21 Limits of Calibration Adjustments...22 RF Output Power Test Setup...30 RF Leakage Test Setups...31 Assembly Breakdown...50 RF Output Waveforms...56 A1 PWB Waveforms...57 A2 PWB Waveforms...58 Nominal HV vs. Power Setting...59 Top Assembly Parts List, Interconnect and Functional Block Diagrams...61 A1 Control/Display PWB Parts List, Layout and Schematic...62 A2 Power PWB Parts List, Layout and Schematic...63

Table

Title

3.1 4.1 4.2

POST Test Sequence...24 RF Output Power Test Limits...29 RF Output Calibration Target Currents...33

Page

Page

2000

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2000 1.0 GENERAL INFORMATION 1.1 Foreword This Service Manual has been prepared to guide the qualified biomedical electronics technician through all aspects of preventative maintenance and repairs necessary to keep the Hyfrecator® 2000 Electrosurgical Unit (ESU) up to original factory specifications. CONMED Corporation reserves the right to alter the specifications of the Hyfrecator® 2000. It is important to have access to the Operator’s Manual supplied with each unit in order to restore original specifications. The Operator’s Manual may also lead to a better understanding the unit’s unique features and what the user may expect from it. The current version of the Hyfrecator® 2000 Operator’s Manual may be ordered from CONMED, as indicated on the inside front cover of this manual. Although this ESU has been designed for many years of trouble-free use and features a number of designedin aids to simplify maintenance, it is assumed that the technician servicing the Hyfrecator® 2000 has a basic understanding of digital, analog and high-frequency power electronics, including through-hole printed wiring board (PWB) component replacement methods, and is familiar with troubleshooting using an oscilloscope and digital voltmeter. Further, the technician should be able to perform standard biomedical safety testing, such as measuring low-frequency leakage current. The service technician should have ordinary electronic service tools and test equipment at his disposal. In addition, nearly all service actions include verification of RF output power calibration using an electrosurgical tester, or equivalent bench setup, capable of presenting 200, 500 and 1000 ohm non-reactive loads and able to measure RMS RF currents from 40 to 400 mA with a traceable accuracy of at least 5%. Although not essential, a high voltage, high frequency oscilloscope probe, such as the Tektronix P6015A can be a useful troubleshooting tool. A properly equipped bench should also have a functioning Hyfrecator® 2000 handswitched accessory on hand to facilitate normal testing and service. This accessory may be ordered through CONMED Customer Service. The Hyfrecator® 2000 has been certified for conformance to: • Underwriters Laboratories UL544 • Canadian Standards Association CSA 22.2 #125 • IEC 60601-1 1.2 Intended Use The Hyfrecator® 2000 ESU is intended for use only by physicians for purposes of minor surgical treatments where electrosurgical desiccation, coagulation or fulguration is indicated for hemostasis or tissue destruction. It may also be used for excision of lesions where marginal thermal damage is not contraindicated. As with all ESUs, these effects are achieved through passage of high-frequency current originating at the active electrode through the patient’s tissue. This current is in the 500 kHz range to prevent neuromuscular stimulation. Current injected into the patient may be returned to the ESU via several possible paths: • In monopolar applications, where a single-pole active electrode is used at the surgical site, current may be returned either through a large-area return electrode in contact with the patient’s skin, or simply through the patient’s body capacitance to earth. The current is then returned through the green-yellow earth conductor in the unit’s mains power cord. The return electrode jack is capacitively referenced to earth.

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2000 • In bipolar applications, two-pole active electrodes or forceps are used, and the current simply passes through the tissue pinched between these two poles, with negligible involvement of an earth path. Some of the intended effects rely on a hot electrical arc being struck between the monopolar active electrode and the target tissue. These arcs require peak voltages in the kV range, and thus can present a burn hazard to the technician. See Section 2.3 for methods to avoid this hazard. 1.3 Warranty As manufacturer of the CONMED HYFRECATOR® 2000 and other high quality medical equipment, CONMED warrants all of its products to be free from defects in material and workmanship under normal operation and use. The warranty period for the CONMED HYFRECATOR® 2000 is twelve (12) months to the product’s original owner. NOTE: The warranty card must be returned by the original owner to CONMED within ten (10) days of receipt of the invoice. A ninety (90) day warranty is provided for standard and optional accessories. The ninety (90) day warranty includes the power up/down switching handle and cord. There is no warranty on disposable, single-use items. The warranty is limited to the repair or replacement (at the manufacturer’s discretion) of any HYFRECATOR® 2000 (or part thereof) that is returned to the manufacturer within the specified warranty period and which, after examination, is found to be defective. Transportation of the HYFRECATOR® 2000 must be prepaid by the sender. The unit will be returned prepaid to the owner by the same manner of transportation used in shipping the product to the manufacturer. The warranty does not apply to any product, or integral part thereof, that has been altered or serviced by anyone other than the manufacturer. Nor does it apply toward any product that has been damaged as a result of accident, abuse, misuse or negligence on the part of the user. 1.4 Factory Service CONMED is proud of its long tradition of excellent Technical Service. Expert advice on all aspects of servicing the Hyfrecator® 2000 is available at no charge during normal business hours at the telephone numbers appearing on the inside front cover of this manual. Whether under warranty or not, this unit may be returned to the factory for service. Non-warranty service will, of course, be charged at the current rate. Before returning the unit, contact CONMED Technical Services for return authorization and shipping instructions.

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2000 2.0 PRODUCT DESCRIPTION This Section contains relevant “Quick Start” excerpts of the technical data supplied in the Hyfrecator® 2000 Operator’s Manual, Cat. No. 7-900-OM-ENG. Refer to that document for further details. 2.1 Controls, Displays and Connectors The Hyfrecator® 2000 controls are marked with IEC and ISO symbols which should be familiar to an experienced biomedical technician. See the Operator’s Manual, Section 3, for detailed definitions. • Mains Power AC Mains power is controlled by a rocker switch on the right-hand side of the unit. Mains power is supplied by a 3-conductor cord connected to the CEE-22 mains inlet on the bottom of the unit. This cord MUST be connected to a safety-earthed AC mains source corresponding to the unit’s mains rating marked on the rear. The green-yellow lead in this cord serves to return monopolar RF current to the unit through the patient’s body capacitance to earth. • Mode Selection A three-position slide switch marked “HI - LO - BI” sets the operating mode. This switch also exposes only the RF output jacks appropriate to the selected mode. The active accessory RF plug must be disconnected from the RF jacks to allow movement of the mode switch. • Power Adjustment RF output power may be adjusted using either the power control knob or the up/down push-buttons on the handswitched active accessory. The selected power in watts to rated load appears on the two-digit LED display. HI and BI may be set in 1 W increments from 0 to 35 W, and LO is adjustable from 0.0 to 9.9W and 10 to 20 W. Note that each mode has its own independent power setting. • Output Activation Activation of RF output is controlled by either a handswitched accessory or an optional footswitch connected to the four-pin quick-release connector on the bottom of the unit. Activation is accompanied by illumination of the blue LED below the power display and a steady, audible tone. • Tone Volume The activation tone volume may be set using the screwdriver adjustment on the rear panel. The tone remains audible at the minimum setting. • RF Output Connections P/P (Patient Plate): Recessed male 0.08" (2 mm) pin for connection to the optional Patient Plate cord. Serves as an RF current return pole for Monopolar output. It is also capacitively coupled to earth via the mains cord to couple return current through the patient’s body capacitance when a patient plate is not in use. HI and LO: Monopolar active output, capacitively referenced to earth and the P/P jack. Intended for connection to the 0.25" (6 mm) RF banana plug on monopolar active accessories.

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2000 BI: Two 0.25" (6 mm) jacks for connection to a two-conductor bipolar active accessory cord. These connections are not referenced to earth or the P/P connector. 2.1.1 Power Setting Storage Upon each power-up, the power settings for all three modes are returned to the values previously stored. During use, settings are automatically stored to non-volatile memory (EEPROM) each time the following sequence occurs: 1. Any power setting is changed, AND, the unit is activated, OR, the mode is changed, OR, 2.5 seconds pass without a power adjustment. Setting changes made immediately before powering down will not be stored. Mains power is not required to retain these settings, and the expected EEPROM storage life is greater than 10 years. Some service actions such as recalibration will alter the stored settings. As a favor to the user, note the power-up settings when the unit is received and restore them before returning it to service. If the stored settings are unknown, it is safest to set them all to zero. 2.2 Specifications Refer to the Operator’s Manual supplied with the unit you are servicing for the complete set of specifications for that unit. The following partial specifications apply to units in production at the time this manual was revised, and are only those relevant to service actions. Mains: All models are rated for 50-60 Hz AC single-phase mains power. Catalog Number

Mains Voltage, V +/- 10%

Mains Current, A, maximum

Mains Fuses, 5x20mm Type T

7-900-100 7-900-115 7-900-220 7-900-230

100 115 220 230-240

0.9 0.8 0.5 0.5

1.25A 1.25A 0.63A 0.63A

Note: Mains ratings as supplied from the factory are marked on the rear panel nameplate. See Section 2.4 for instructions on altering the mains voltage rating. Mains cord: 3 conductor #18 AWG (1.5 mm2) Cu, 10 ft (3m), UL SJT with IEC-320-C13 (250 V 6 A) inlet connector. Safety: IEC Ratings: Class 1, Type BF Defibrillator-proof. Patient 50/60 Hz risk current without earth connection: <50 µA Calibration Accuracy (RF power output to Rated Load vs. Power Display):

LO and BI: HI:

4

0 to 10 W: Greater of 90 mW or 10% of setting 10 to maximum setting: 10% of setting Greater of 1 W or 10% of setting

2000 Environmental: Operation: 50oF to 104oF (10oC to 40oC); 10-95% Relative Humidity, non-condensing Storage: -40oF to 158oF (-40oC to 70oC); 0 -95% Relative Humidity, non-condensing Output Ratings: Mode, W

Power, max

Load, Ohms

Voltage, KV(p-p)

Pulse Rate, KHz

HI LO BI

35 20 35

1000 500 500

8.0 3.0 3.0

24.2 32.3 32.3

Duty Cycle: Intermittent, 30s/30s active/idle Output Waveform: Clipped, damped sinusoid with 450 +/- 50 KHz dominant frequency repeated at pulse rate shown above. See section 5.1.4 for RF output oscillograms. 2.3 Service Precautions WARNING: Shock Hazard Hazardous voltages are accessible when the enclosure is opened. Mains component terminals and components in the HV power supply and RF Power Amplifier present a lethal shock hazard. • Disconnect the mains cord during any service action which does not require power. • High voltage on the PRHV filter capacitors may require more than 90 seconds to bleed down to 10V after mains power is removed. Wait until the red LED A2DS1 becomes dark before working in this area of the Power Board. • High voltage in the intermediate circuitry is well isolated from earth and thus presents negligible risk, EXCEPT when this circuitry is earthed via test probes or to avoid a burn hazard. (See below.) WARNING: RF Burn Hazard DO NOT touch RF output terminals or internal components while the unit is activated. This unit is intended to produce thermal lesions (burns) in living tissue. These effects will be produced inadvertently if the RF output circuitry or related components are touched while the unit is activated. The intermediate circuitry, including the mains transformer frame, is isolated from earth and is lightly coupled via stray capacitance to the RF output. Therefore, mild but alarming burns or “shocks” may occur if intermediate components are touched during activation. This risk may be avoided by connecting the GND test point A2TP1 to earth ground while troubleshooting. However, this action also increases the risk of a shock hazard from HV components. CAUTION: Thermal Burn Hazard Hazardous temperatures may appear on some component surfaces. During and after activation, power conversion devices, especially those bearing heatsinks, may develop surface temperatures hot enough to burn skin. Burn risk may be minimized by avoiding contact with these components until they have cooled, and by minimizing activation time and duty cycle.

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2000 CAUTION: Component damage is possible during service. Improper service practices may destroy sensitive components in this unit and may void the warranty. Observe sound, conventional electronic service practices, with particular attention to the following: • Electrostatic Discharge (ESD): This unit contains ESD sensitive components. Use effective ESD suppression techniques during all service actions. • Common-Mode High Voltage: Whenever mains power is applied, and especially when the unit is activated, high common-mode voltages will appear on all parts of the intermediate circuitry. Connect circuit common A2TP1 to earth ground before making measurements. Even small currents drawn through earthisolated test probes or body capacitance may destroy some sensitive semiconductors. • Minimize Activation Time: This unit will overheat during continuous activation, especially with low impedance loads. Observe rated duty cycle. Restrict activation into short circuit loads to less than 5 seconds. • Component Replacement: Replacement components should be as specified in the parts lists in Section 5 of this manual. Consult CONMED Technical Services for custom components or acceptable substitutes. • Housing fasteners: To avoid stripping threads during reassembly, rotate housing screws counterclockwise with light pressure to find the original threads in housing bosses. CAUTION: Test Equipment damage possible during service. This unit produces voltages which may exceed common test equipment ratings. To avoid damage to your equipment, ensure that their ratings are adequate, with particular attention to the following: • The common mode peak RF voltage in the intermediate circuitry may rise as high as several kV during activation. Connect A2TP1 GND to earth to avoid this hazard. • Peak RF output voltages with respect to earth may exceed 8000 V. Common oscilloscope probes will arc over at this level and may destroy your oscilloscope input circuits. Do not attempt to measure RF output voltage unless your oscilloscope probe is adequately rated. • Use only heavily insulated test leads in good condition on RF output connections. Ordinary test leads may break down and allow output current to flow through unintended paths.

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2000 2.4 Mains Voltage Strapping This unit may be field-strapped to any of the rated mains voltages shown in Section 2.2 of this manual. Use the following procedure: 1. Unsolder the zero-ohm resistors from the A2 PWB, JP1 through JP5 and reinstall them for the desired mains rating according to Table 1 in Figure 5.8. Insulated, solid hookup-wire jumpers may be used instead of zero-ohm resistors. 2. Replace mains fuses A2F1 and A2F2 per Table 2, Figure 5.8. 3. Use an indelible marking pen to alter the mains voltage and current ratings on the nameplate according to Section 2.2 specifications. DO NOT alter the model number or serial number. 4. Reassemble the unit, connect it to the new mains voltage source and perform Mains Leakage and RF Power Output testing according to Section 4.2 of this manual. 2.5 Environmental Protection At the end of its service life, the Hyfrecator® 2000 should be disposed of locally in accordance with local regulations. Component materials are: • Thermoplastic enclosure and stainless steel mounting plate. • Thermoset printed wiring boards containing miscellaneous electronic components. • Power transformer made of steel and copper. • Mains cord and pencil accessory made of thermoplastic and copper. • Accessory electrodes are stainless steel and thermoplastic. • Electrodes contaminated with biological waste should be disposed of as biologically hazardous material. • Shipping container and packing material are a combination of cardboard and plastic film.

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2000 3.0 THEORY OF OPERATION The Hyfrecator® 2000’s fault detection and Fault Code displays expedite troubleshooting. However, the biomedical technician must understand more fully how the unit was designed to operate in order to isolate and repair less common problems. This Section is intended to provide that background. 3.1 Overview The Hyfrecator® 2000 electronics comprises two printed wiring board (PWB) assemblies, the Display/Control Assembly (A1), and the Power Assembly (A2). Refer to Figure 5.6 for a block diagram of the system. Component reference designators are formally listed as the assembly first, the component second, then the pin number. Example: Pin 5 of U3 on the Power board assembly would be referred to as A2U3-5. The A2 Power Assembly contains most of the power supplies, the Radio Frequency (RF) Power Amplifier (PA), the RF output circuitry, the accessory switch isolation, the volume control, speaker amplifier and speaker. These functions are controlled and monitored by the A1 Display/Control assembly, which contains the Control microcontroller, the Monitor microcontroller, calibration and power memories, LED displays, mode selector switch, some of the power supply, and the power setting encoder. The following sections detail the circuit operation of each of these blocks. With the exception of the line voltage side of T1 and the monopolar (HI & LO) patient connection circuitry, all of the Hyfrecator® 2000 circuitry is isolated from ground. The patient connections are capacitively RF referenced to earth ground. As a result of the circuitry isolation, an external safety ground (earth) lead must be connected to the intermediate circuit signal common ground to make meaningful measurements and to avoid damage to components, test equipment and yourself. 3.2 A2 Power PWB Refer to Figure 5.8 for a schematic diagram of this PWB. The “A2” reference designator prefix for components may be assumed, as it is not used in the following description for clarity. 3.2.1 Power Supplies AC mains power is isolated and converted to several low voltage and one high voltage (HV) source of DC power used by other circuitry. 3.2.1.1 Mains & Isolation AC mains (line) power enters through a detachable cord and is routed through the power switch on the side of the unit. From the switch, mains power passes through Fuses F1 and F2, which guard against overcurrent faults. The fuse ratings correspond to the unit’s mains voltage rating (See Figure 5.8, Table 2). Earth ground is connected directly from the mains inlet connector to the patient circuitry on the A2 assembly. Its main function is to provide a functional earth return for monopolar RF current when no patient plate is in use. Interruption of the earth conductor does not create a shock hazard, but it may allow the patient plate voltage to become high enough to cause a burn to the user or patient.

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2000 The Hyfrecator® 2000 is powered from the 50-60 Hz AC mains at one of four strappable voltage ratings. The factory selection appears on the nameplate on the rear of the enclosure. Mains voltage selection is made on the A2 Power PWB using jumpers JP1-5. See Figure 5.8, Table 2. The procedure for changing the mains voltage is in Section 2.4 of this manual. Transformer T1 provides mains isolation and converts the AC mains voltage to those AC voltages required by the internal DC power supplies. Note that the secondary windings are protected by embedded, nonreplaceable thermal fuses. These fuses will open only if an unusual overload fault causes the winding temperature to become dangerously high before the mains fuses can open. 3.2.1.2 Low Voltage Supplies Low voltage DC power, +24UNREG, is derived from the full wave rectified and filtered output of the low power secondary, T1-16 and T1-18. VR1 produces the +12 volt regulated power, +12V. A low current source of regulated +5 VDC for A2 circuitry, +5VR, is provided by U2-14. +24UNREG and +12V power the A1 Display/Control PWB as detailed in Section 3.3.5.3. 3.2.1.3 Pre-Regulated High Voltage (PRHV) Supply Unregulated high voltage dc power, PRHV, is derived from the full wave rectified and filtered output of the high power secondary of T1-13 and T1-14. Resistor R15 and LED DS1 act as an indicator that high voltage is present, and as a bleeder to discharge filter capacitor C13. PRHV provides about +150 VDC bulk power to the High Voltage (HV) Switching Regulator that feeds the RF Power Amp. 3.2.1.4 High Voltage Switching Regulator RF output power varies approximately as the square of the HV voltage. The value of HV during activation is set by A1 signal VCON, in accordance with the user’s power setting for a given mode. See Figure 5.5 for nominal HV voltage vs. power setting. Switchmode controller U2 and power FETs Q2 and Q4 are the major active components of a buck switching supply that chops PRHV down to the RF PA supply voltage, HV. HV is regulated to (R33+R31)/R31, or about 20 times VCON when /HVEN is low. When /HVEN is high, the power supply shuts off, and HV bleeds off to under 1V over several seconds. R20 and C7 form part of a freerunning sawtooth oscillator which sets the switching frequency to approximately 1/(R20*C7), or about 90 kHz. Q2 and R37 drive the gate of P-channel MOSFET Q4; when Q2 is on, Q4 is on. R36 provides Q4 turnoff gate bias, and diodes D5 and D6 protect the gate of Q4 against over voltage. This DC drive combination allows Q4 conduction duty cycles to vary over a much greater range than would be possible with a gate drive transformer. When Q4 is switched on, the current through L1 and into C12 and C18 ramps up, causing HV to rise. When HV reaches a voltage set by VCON and a sawtooth waveform at U2-5, Q4 is switched off by U2. D4 then conducts the inductor current, which then begins to ramp down. The conduction duty cycle of Q4 is roughly proportional to the ratio HV/PRHV. Thus if PRHV increases, the Q4 conduction time decreases, or as VCON increases, the on-time increases. R34 is the first stage of a voltage divider for the High Voltage Sense (HVSENS) monitoring circuit located on the A1 PWB.

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2000 3.2.2 RF Generation Voltage-controlled DC power from the HV regulator is converted to radio frequency (RF) output power by the RF Power Amp and coupled to the RF Output jacks through the patient circuits. The output power of the unit is determined by the gate pulse width and frequency, and the high voltage supply, HV, to the RF Generator. All of these parameters are set by the Control microcontroller on the A1 PWB. 3.2.2.1 RF Gate Drive & Monitor The 24-33 KHz RF gating waveform /GATE from the A1 PWB is amplified and inverted by U1A to drive the gate pin of RF PA MOSFET Q3. The /GATE waveform is fixed by the mode selection and does not vary with power setting, except that no gate drive is generated at zero power settings. R6 feeds a sample of the Q3 gate waveform, GATEMON, to a duty cycle monitor on the A1 PWB. 3.2.2.2 RF Power Amplifier (PA) When /GATE is low, Q3 switches on, and current ramps up in the primary of T3, building energy in its magnetic field. When /GATE goes high, Q3 turns off, and T3’s magnetic energy is released into the resonant RF output circuits. Capacitor C20 and the primary inductance of T3 form a resonant circuit which determines the 450 KHz component of the RF output. Unconstrained, this ringing RF waveform would normally swing negative and forward bias the slow intrinsic diode in Q3. This power-wasting process is averted by fast recovery diodes D7 and D8 which clamp the ringdown voltage to ground and shunt the swinging current back into the HV supply. These diodes are responsible for the clipped appearance of the RF output waveform. 3.2.2.3 Patient Circuits T3 steps its primary RF voltage up to the final levels for effective surgical use. Capacitor C37 provides the connection for return RF current through the earth lead in the mains cord for use in monopolar mode with no return plate. Coupling capacitor C36 and J8 provide a return path for the optional patient plate. Accurate RF power measurements may be made using either the patient plate connection or earth. C31, C32, and C38 provide additional high pass filtering to reduce neuromuscular stimulation and to provide some load regulation curve shaping. Bipolar (BI) RF output is developed by a separate T3 secondary to output jacks J6 and J7. This circuit is isolated from both earth and the patient plate connection, thus providing a fully isolated bipolar output. 3.2.3 Isolated Switch Detector The push-button switches in the handswitching accessory share a common conductor with the RF output voltage. The Isolated Switch Detector conveys switch closure information to the intermediate circuitry on the A1 PWB while maintaining common-mode electrical isolation via a combination of magnetic and optical coupling. This circuit also operates with the optional footswitch.

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2000 T2 and Q5 form a self-oscillating power inverter which converts +12 VDC into a 45 KHz AC voltage across the primary of T2. Q5-b is biased into initial conduction by R38 & R39, aided by feedback winding T2-2&3. When T2 primary current rises to about 200 mA, the T2 core saturates, and the feedback winding reverses polarity, switching Q5 off. T2’s energy then rings with C25 for 1/2 cycle, after which Q5 turns on again for another cycle. The 45 KHz AC secondary voltage, T2-5&6, is rectified and filtered by D9 and C30 to produce the Isolated Power Supply (IPS) of about 5.3 VDC with no load. Connector J2 is located on the bottom of the unit and accepts the plug from either a handswitch accessory or a footswitch. When the footswitch is used, only the /ACTIVE signal and IPS- are used, and there is no connection to the RF lead. When the handswitching accessory is used, IPS- is connected to the RF lead and acts as a common lead for the power increase (/HPUP), power decrease (/HPDN), and activation signals (/HACT). Each of these switch closures connects IPS power to the LED of an associated optoisolator (U3, U4, or U5), the phototransistors of which which develop signals /ACTIVE, /POWUP and /POWDN via +5V pullups on the A1 PWB. 3.2.4 Tone Generator and Monitor Activation and alarm tones are developed on the A1 PWB as a 5V CMOS signal, /TONE. The A2 Tone Generator amplifies /TONE and delivers it at an adjustable volume level to loudspeaker LS1. Buffer U1B inverts /TONE and boosts it to 12V. Screwdriver-adjustable volume potentiometer R47 and R14 set the level of the tone signal fed to emitter follower Q1, which then drives 60 Ω speaker LS1. Tone Monitor circuitry samples the LS1 audio voltage and develops a proportional analog signal TONEMON which is used by the A1 monitor to determine activation tone presence. TONEMON varies from about +0.12 V at minimum volume to about +4.5 V at maximum. 3.3 A1 Display/Control PWB Refer to Figure 5.7 for a schematic diagram of this PWB. The A1 Display/Control Assembly performs the following functions: User Interface: • Power setting display for selected Mode. • Power adjustment by front panel knob and up/down switches on the 3-button accessory. • Non-volatile (EEPROM) storage of power settings. • Generation of button clicks and activation tones. • Activation in response to hand or foot switch closures. • Illumination of the blue Activation LED. • Fault code generation and display. RF Output Control: • PA drive waveform generation per selected mode. • HV Supply voltage control per the power setting.

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2000 Fault Detection: • Stuck activation or power adjust button on power-up. • Incorrect waveform frequency or duty cycle. • Incorrect HV voltage. • Activation tone failure. • Corrupted EEPROM calibration data. • Incorrect LED power display. • Microprocessor malfunction. Fail-Safe RF Shutdown: • Two redundant PA drive shutdowns. • Two redundant HV shutdowns. Service mode: • Tools-only access via internal jumper. • Mode switch selection of Calibration, diagnostics (Pseudorun) or Last Fault Code recovery. • Two-point calibration for each Mode from user controls; no trimming potentiometers or selected components. • Protected EEPROM storage of last calibration settings. 3.3.1 Dual-Channel Architecture The A1 assembly incorporates two independent microcontrollers for Control (U1) and Monitor (U2). Both microcontrollers are single-chip Microchip® PIC16C RISC devices, each incorporating program ROM, RAM, clock oscillator, reset generator and 5-channels of 8-bit analog-to-digital conversion (ADC). Each microcontroller operates with its own 1K bit serial Electrically Erasable Programmable Read Only Memory (EEPROM), U3 and U4. All of the Hyfrecator® 2000’s normal functionality is provided by the Control microcontroller. The Monitor microcontroller serves only as a “watchdog”, searching for combinations of signals appearing in the control channel which are indicative of potentially hazardous faults. Except during Power On Self Test (POST) and upon detection of a fault, the Monitor microcontroller’s function is transparent to the Control microcontroller. The only normal user function provided by the Monitor microcontroller is illumination of the Active LED. The two microcontrollers and their associated hardware are well isolated from one another, such that no single component failure occurring during a procedure can allow a hazard to persist for over 1/2 second. For example, each microcontroller has its own +5V regulator, each supplied from different sources. Input signals provided to both microcontrollers are resistively isolated to prevent a shorted input pin on one microcontroller from corrupting the signal read by the other. This dual-channel architecture and fault detection process has successfully passed IEC 60601-1-4 Functional Safety testing and virtually guarantees that no patient or staff injury can result from a single system component failure.

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2000 3.3.2 A1 Signal Descriptions This section describes all signals present on the A1 PWB. 3.3.2.1. Mnemonic Conventions Signal mnemonics use the following conventions: • A leading slant (/) indicates a logic signal which is active low. • A “.C” or “.M” suffix indicates a signal specific to the Control or Monitor microcontroller, respectively. • In general, a leading V indicates an analog signal. The “A1” reference designator prefix for components may be assumed, as it is not used in the following sections for clarity. 3.3.2.2 Signal Levels All logic signals are nominal 5 V CMOS rail-to-rail levels (GATEMON excepted). All analog signals fall in the 0.0 to +5.0 V range. Microcontroller ADC reference voltages are identical to the local Vdd (+5C or +5M). All signal voltages are referenced to A1 signal common (GND A1TP3). 3.3.2.3 DC Power Signals Control power is provided by unregulated +24 V (+24U) from A2 and feeds TO-220 +5V 2% regulator VR2 to supply +5C (A1TP4). Monitor power is supplied from +12V, and is regulated down to +5.0 V +/- 2% (+5M) on A1TP5 by TO92 regulator VR1. 3.3.2.4 External Input Signals /ACTIVE - Activation hand or foot switch closed. /POWDN - Accessory power down button closed. /POWUP - Accessory power up button closed. HVSENSE - Analog signal proportional to HV (42.3 mV/V). R5 forms the lower half of the HV voltage divider string. TONEMON - From A2 tone drive monitor. +0.10 V minimum with tone active. GATEMON - Same as PA GATE drive (0/+12V). 3.3.2.5 External Output Signals VCON - HV setpoint voltage (19.66*VCON); +5C x HVPWM duty cycle. /GATE - CMOS-level PA gate drive (active low). /TONE - Audible tone drive signal. /HVEN - HV power supply enable.

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2000 3.3.2.6 On-Board I/O Signals • /φ1, /φ2 - Two-bit grey-coded rotary encoder output (power adjust). • SDA, SCL - IIC serial EEPROM data and clock signals (.C & .M) • VCAL - Three-state analog signal representing Service jumper (J2) presence (0.0V), normal run (+5.0V) or Monitor microcontroller fault status (+2.5V) to Control microcontroller. • VGATE - Driven by GATEMON analog duty cycle monitor signal. Nominally +2.1 to 2.6 V, GATE active. • /GATE.M - Isolated version of /GATE; used for PA drive frequency monitor. • GATENA - Monitor GATE enable; forces PA drive off via Q3 when low. • PSETO.0:7 - LED segment drive and Control-to-Monitor settings/fault code signal bus. • LED1:8 - LED anode drive, current limited by RN1. • LED1S - Ones LED digit drive. • LED10S - Tens LED digit drive. • /GATEPWM - PA gate drive signal; frequency and duty cycle determined by Mode selection. • HVPWM - Variable duty cycle CMOS signal; same frequency as /GATEPWM. Sets HV voltage per power setting. (see VCON above). • VMODE - Three-state analog representation of Mode switch position. 3.3.2.7 Control/Monitor Communication The two microcontrollers communicate with one another via three paths: • Functional ESU Signals: i.e, HV voltage, gate frequency, duty cycle, and tone generation. Direction is from Control to Monitor. • 10-bit LED drive bus (PSETO0:7, LED1S, and LED10S): Direction is from Control to Monitor during normal Run Mode. During POST and Fault Code display, the direction is from Monitor to Control. • VCAL Signal: From Monitor to Control. Upon detecting a fault,the Monitor pulls VCAL.M to ground, and through the voltage divider formed by RN4A and RN4B, causes VCAL.C to go to about 2.5 VDC. 3.3.3 Power-Up Behavior When power is applied, +5M and +5C will rise towards their regulated voltage levels. These voltages are presented to the /MCLR (Master Clear) inputs of each microcontroller. After reaching about +4.2 Vdc, and each microcontroller 4 MHz clock oscillator has started, the microcontrollers begin executing their programs stored in on-board program memory. These programs set up I/O ports, read and validate data from their respective non-volatile EEPROMS, and perform some error-detection processes, such as stuck-on faults on any of the three accessory button signals, /ACTIVE, /PWDN and /POWUP. Both microcontrollers then check their VCAL inputs to determine which operating mode to enter. 3.3.4 Operating Modes The Hyfrecator® 2000 can power up in either of two modes, Run or Service. • Run Mode: Used in normal clinical service. • Service Mode: Accessible only when the unit’s enclosure is opened.

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