SERVICE BULLETIN. Description: VOX\ICS Tie Line Subassembly Document #: AMS44\603-0 Service Bulletin #: 002

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1 SERVICE BULLETIN NAT Part #: AMS44 Description: VOX\ICS Tie Line Subassembly Document #: AMS44\603-0 Service Bulletin #: Planning Information 1.1 Applicability All dual channel audio controllers: AMS42, AMS44, AA92H and AA Reason The ICS tie line is coupled to the mic audio before the VOX circuitry. The audio is present on the ICS tie line even if the VOX threshold is not triggered. When the audio controller is used in an installation that is comprised of more than one NAT audio controller the audio may be heard by others, but not by the person speaking. The introduction of an audio gate in the circuitry solves the above problem but also changes the impedance of the ICS Tie Line. The ICS Tie Line impedance must not vary whether the AMS-001 is active or inactive. 1.3 Description The audio path is modified such that the VOX threshold must be triggered to allow the audio on to the ICS Tie Line. This is accomplished with a small subassembly which contains a solid state relay. The relay provides an audio gate which is controlled by the VOX circuitry. When the relay is active the ICS audio path is switched on to the ICS Tie Line and the second ICS amplifier. When the relay is not active the ICS audio path is switched open and the ICS Tie Line is switched to a load to maintain its impedance. The NAT part number for this subassembly is AMS-001. C322 and R335 are combined onto the subassembly as C401 and R402 respectively. The sensitivity of the VOX detector was decreased to maintain the VOX range. To accomplish this R260 is changed from 100K to 47K. Document #: AMS44\ March 9, 1995 Page 1 of 6

2 NAT AMS44 Service Bulletin # Compliance Customer option. NAT recommends this change be accomplished on all dual controllers in installations which include more than one audio controller. Note: This Service Bulletin is applicable to MOD #8. MOD #7 and service bulletin AMS44\ apply to Rev 1.00 of subassembly AMS-001. MOD #8 and this service bulletin apply to Rev 1.10 of subassembly AMS-001. MOD #8 obsoletes MOD #7. Customers with MOD #7 should contact NAT customer service for upgrade procedure to MOD # Approval No change to existing approval. 1.6 Costing Labour One (1) hour estimated, includes required test time. Not warranty reimbursable Parts Mod Kit, NAT p/n , will be available for this modification. Consult factory for pricing and delivery. This modification incorporates a design improvement and does not constitute changes to correct a malfunction. The modification is therefore not subject to warranty consideration. 1.7 Special Equipment Required None. 1.8 Weight and Balance No effect. 1.9 Electrical Load Data No effect. Document #: AMS44\ March 9, 1995 Page 2 of 6

3 NAT AMS44 Service Bulletin # References SM01 Service Manual Other Publications Affected None The next edition of the service manual will include the changes described in this bulletin. 2. Procedure Instructions 2.1 Modification Procedure Both the top and bottom main PCB's will need to be removed from the chassis. Refer to Service Manual SM01, section 5, for details regarding disassembly of the audio controller. The audio controller contains components which are sensitive to discharge of static electricity. Follow the necessary precautions while performing these procedures Bottom PCB (see drawing number AMS44\972-0) - Remove C322 and R335 from the bottom PCB. - Solder the wire leads of P402 to the locations shown on drawing number AMS44\ On the solder side of the PCB, solder in the jumper shown on the drawing Top PCB (see drawing number AMS44\972-1) - Remove IC206 and its 14 pin socket. Cut the trace from pin 6 to pin 10 on the component side of the pcb. Solder in the new 14 pin socket supplied and insert IC206 (4001). If needed, there is a spare 4001 supplied in the mod kit. - On the component side of the pcb, identify the trace that goes from H204, pin 11 to the input of the VOX detector circuit (C242). Cut the trace near C On the solder side of the pcb, cut the trace that goes from pin 10 of IC206 to pin 8 of IC201. Solder a jumper between pins 7&8 of IC201 and between pins 6&7 of IC Remove R260 (100KΩ) and replace it with the 47KΩ resistor supplied in the mod kit. Document #: AMS44\ March 9, 1995 Page 3 of 6

4 NAT AMS44 Service Bulletin # Solder the leads of P401 and the strain relief wire to the locations shown on drawing number AMS44\ Installation of Subassembly AMS-001 to the Bottom PCB - From T301 and T302, remove the two lock nuts closest to the connector J301. Install the two supplied standoffs in place of the lock nuts. Attach the subassembly AMS-001 to the standoffs with the lock-washers between the PCB and the screw heads Clean all reworked areas, then recoat those areas with Conformal Coating Connect P401 and P402 to subassembly AMS-001 and reassemble the audio controller. 2.2 Testing Procedure Acceptance Test Procedure Amendment Perform operational tests of system in accordance with NAT Acceptance Test Procedure in Service Manual SM01. Special consideration should be given to the changed performance of the ICS TIE Line. With the test set configured to allow monitoring of the ICS TIE Line, set the unit for HOT MIC ICS operation and speak into the mic; audio should be observed on the TIE Line. Rotate the VOX control fully ccw (not PTT ICS) and speak into the mic; no audio should be present on the ICS TIE Line. Configure the test set to allow audio signal injection on the ICS TIE Line and monitor the headset output, at maximum volume. Inject audio on the ICS Tie Line, rotate the VOX control from ccw (not PTT), to fully cw, the headset audio shall not change more than 50 mv between the two VOX extremes. 2.3 Identification Procedure Blacken out # 8 on the MOD STATUS tag to indicate this modification has been incorporated. Document #: AMS44\ March 9, 1995 Page 4 of 6

5 NAT AMS44 Service Bulletin # Material Information Mod Kit is required to modify one dual audio controller to MOD 8 status. It contains the following parts: MFR. P/N IDENT DESCRIPTION OR VALUE PACKAGE NAT P/N QTY. IC206 CMOS Quad 2-Input NOR gate 4001 DIP R260 1/4 W 5% Carbon Film 47 KΩ RC SA1 VOX/ICS Tie Line Iso. Subassembly AMS M Pin Crimp DIP Socket #22 AWG Teflon (Blue) wire 10" #22 AWG Teflon (White) wire 8" #22 AWG Teflon (Blue) wire 6" #22 AWG Teflon (Yellow) wire 6" #22 AWG Teflon (Orange) wire 6" #22 AWG Teflon (Black) wire 6" #22 AWG Bus Wire with Teflon Insulation (strain relief) 1/4" #22 AWG Bus Wire with Teflon Insulation (2 X 1/2" jumpers) 1" 4. Diagrams Drawings for Service Bulletin # AMS44\ follow this page. DRAWING REV. DESCRIPTION TYPE AMS-001\ VOX/ICS Tie Line iso. subassembly Schematic AMS-001\ VOX/ICS Tie Line iso. subassembly Parts List AMS-001\ VOX/ICS Tie Line iso. subassembly Component Locator AMS44\ AMS42-3 (bottom board mods) PCB Modifications AMS44\ AMS42-2 (top board mods) PCB Modifications Document #: AMS44\ March 9, 1995 Page 5 of 6

6 NAT AMS44 Service Bulletin # 002 Drawings for Service Bulletin # AMS44\ precede this page. End Of Service Bulletin Document #: AMS44\ March 9, 1995 Page 6 of 6

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9 PARTS LIST NAT Part #: AMS-001 Description: VOX\ICS Tie Line Subassembly Document #: AMS-001\701-0 Rev: 1.10 MFR. P/N IDENT DESCRIPTION OR VALUE PACKAGE NAT P/N QTY. CAPACITOR C401 Tantalum, 16V 33 uf CONNECTORS J401 2 Pin 90 deg MTA Header J402 4 Pin 90 deg MTA Header P401 2 Pin MTA Connector P401 4 Pin MTA Connector INTEGRATED CIRCUITS U401 Solid State Relay AQW614A DIP RESISTORS R401 1/4W 5% Carbon Composite 2K R402 1/4W 5% Carbon Composite R403 1/4W 5% Carbon Composite R404 1/4W 5% Carbon Composite MISCELLANEOUS (MECHANICAL) PARTS M401 PCB Rev M402 1/4" x 3/8" 4-40 Standoff M Panhead Screw M404 Lock Washer Split Ring 3mm End of Parts List Rev 1.10 March 8, 1995 Page 1 of 1

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