FOR 2U57- EXTENDED FREQUENCY RANGE MODIFICATION KIT Kit for modification of ARC Type 38A Communication System; (Extended COM Frequency Range: 8. to 36.975 MHz) Part Number Change: From: To: RT-38A - Standard: 456- Extended Range: 456- C-38A - Standard: 4567- Extended Range: 4567- Publication. No. 86M8 JUNE 993
2U57- MOD KIT LIST OF EFFECTIVE PAGES Issue Page Affected Date Title A 6/7/93 2 A 6/7/93 3 A 6/7/93 4 A 6/7/93 5 A 6/7/93 6 A 6/7/93 7 A 6/7/93 8 A 6/7/93 9 A 6/7/93 A 6/7/93 A 6/7/93 2 A 6/7/93 3 A 6/7/93 Page 2
2U57- MOD KIT TABLE OF CONTENTS Section Title Page - Title - List of Effective Pages 2 - Table of Contents 3 - List of Figures 4 - List of Tables 4. General Information 5. Purpose for Instruction Manual 5.2 Affected ARC Radios 5.3 Special Equipment Required 5.4 Reference 5.5 Theory of Operation 5-6 2. Kit Installation Procedures 7 2. C-38A Control Head 7 2.2 RT-38A Receiver Transmitter 7 2.3 Alignment 8 2.4 Mod Decal 8 2.5 Part Number Decal 8 3. Illustrated Part Identification Page 3
2U57- MOD KIT LIST OF FIGURES Figure Number Title Page 2- Side View of Control Head after Switch Replacement 8 2-2 Solder Side View of A3A Board 9 2-3 Part Number and Mod Decals in Installed Positions, RT-38A 9 2-4 Part Number and Mod Decals in Installed Positions, C-38A 3-2U57- Modification Kit 2 3-2 Modified Schematic for A3A Digital PC Board 3 LIST OF TABLES Table Number Title Page 2- Tuning and Frequency Codes 6 3-2U57- Modification Kit 2 Page 4
2U57- MOD KIT SECTION I GENERAL INFORMATION. Purpose of Instruction Manual The purpose of these instructions is to provide a brief description of the extended frequency range modification procedures for the 38A Communication System. Existing radios tune the frequency range of 8. to 35.975 MHz. After the modification kit is installed, the 38A will tune 8. to 36.975 MHz. The replacement parts are Sigma Tek, Inc. kit part number 2U57-. Section III of this manual contains an illustration of the kit parts. This information can be used for future reference, should it become necessary to replace a defective component in the kit. A copy of this instruction manual should be inserted in the maintenance manual of the affected ARC radio..2 Affected ARC Radios RT-38A Receiver-Transmitter C-38A Control Head.3 Special Equipment Required Installation of 2U57- kit requires no special tools or test equipment. Standard equipment such as a soldering iron, desoldering equipment, pliers, wire cutters, screw drivers, etc. is all that is necessary for installation..4 Reference Series Communication System Type 38A Service/Parts Manual - P/N 743, Revised Issue, August 3, 985..5 Theory of Operation.5. Channeling Code - The channeling code changes are as follows:.5.. C-38A Switch Replacement - The replacement switch upgrades from 8 positions to 2 positions with the 2 new positions at 36.xxx MHz. Codes for 8 to 35 remain the same as in the original switch..5..2 RT-38A Programmable Read Only Memory (PROM) Replacement - Integrated circuit A7U7 converts BCD code from the control head to binary code for the synthesizer and the tuning voltage generator. The program change in the new PROM shifts output code down one memory location, which results in a change in Tuning and Frequency Codes as shown in Table. This shift in code allows for the extra frequency 36.xxx MHz..5.2 Master Terminal Count - The master terminal count (MTC) is changed as follows: Original: Master terminal count is 23 for transmit and 24 for receive. Modified: Master terminal count is 23 for transmit and 24 for receive. This change is accomplished by using one of the extra inputs on the 8-input MTC NAND gate. The counter LSB is routed (jumpered) to this extra input which increases the terminal count. Example: At 36. MHz the PROM will send a zero preselect. The counters, A3AU and A3AU2 will start counting at the base count plus the preselect (96 + ). In transmit mode, the master terminal count is set for 23. From 96 to 23 is 36 counts. This times 4 counts from the prescaler 25, times per second yields 36. MHz. Page 5
Table 2- Tuning and Frequency Codes MHz Transmit Receive TUNE CODE (Binary) Frequency Frequency EDCBA Y8 Y7 Y6 8.xxx 9.xxx 2.xxx 2.xxx 22.xxx 23.xxx 24.xxx 25.xxx 26.xxx 27.xxx 28.xxx 29.xxx 3.xxx 3.xxx 32.xxx 33.xxx 34.xxx 35.xxx 36.xxx 28.xxx 29.xxx 3.xxx 3.xxx 32.xxx 33.xxx 34.xxx 35.xxx 36.xxx 37.xxx 38.xxx 39.xxx 4.xxx 4.xxx 42.xxx 43.xxx 44.xxx 45.xxx 46.xxx Page 6
2U57- MOD KIT SECTION II KIT INSTALLATION PROCEDURES 2. C-38A Control Head Reference Service/Parts manual Figure 7-, C-38A Exploded View. 2.. Disassembly Disassemble affected control head to gain access to S. It will be necessary to detach A and A3 printed wiring (pc board) assemblies as well as the front frame assembly (remove Items 39 and 4). Do not remove any any wiring between these assemblies. Remove old S switch and ensure all holes are free of solder. 2..2 Switch Installation (Mod kit part number 45659-2) Remove the new switch assembly from its protective packaging. Slide the shaft of the switch through the hole in the plate assembly (Item 38), through the supplied washer and nut, then through the holes in the plate and panel assembly. Guide switch assembly pins into their respective holes. Tighten nut onto switch. Replace screws and lock washers, (Items 39 and 4). Solder switch assembly pins in place. Replace A and A3 pw boards. See figure 2- of this document for a diagram of the installed switch assembly. 2..3 Assembly Assemble as specified in the radio maintenance manual. 2.2 RT-38A Receiver-Transmitter Reference Service/Parts manual Figure 7-, RT-38A Exploded View. 2.2. Disassembly Disassemble affected RT to gain access to the A7 and A3A pw assemblies. 2.2.2 A7 Modification (Mod kit P/N 4479-243) Reference Figure 7-28, RT-38A Logic, A7 PW Assembly. Note the location of A7U7 pin. Carefully desolder and remove A7U7. Ensure all holes are free of solder. Insert the new IC, and solder into place. 2.2.3 A3A Modification Reference Service/Parts manual Figure 7-6, RT-38A Synthesizer Assembly, A3, Exploded View and Figure 7-7, RT-38A, A3A PW Assembly. Remove A3A board from the main synthesizer assembly. Do not disconnect any wiring. Reference Figure 2-2 of this document. On the back of the pw board, carefully cut the trace connecting U3- and U3-2. CAUTION: Use extreme care in this portion of the procedure. Do not damage any of the surrounding traces when cutting the trace mentioned above. Verify open circuit between U3- and U3-2. On the back of the board, solder an insulated jumper (#22 to #28 AWG) from pin U3- to U4-5. 2.2.4 Assembly Assemble as specified in the Service/Parts Manual. 2.3 Alignment Page 7
2U57- MOD KIT Reference Service/Parts manual section 5-29 for receiver alignment. To properly align the radio, first set the channel frequency to 35.45 MHz and adjust A7R2 for a tuning voltage of.5 Vdc at A9P4-3. Then adjust AT, AL2, AL4, and AL6 for maximum audio output at 8.45 MHz and 36.45 MHz. Repeat maximum adjustments at lower and upper frequencies until no further improvement is obtained. Perform necessary functional tests and align any other circuitry as required. 2.4 Mod Decal (Mod Kit P/N 66A43- for RT- 38A and P/N 66A44- for C- 38A) Remove backing from decal and place as shown in Figure 2-3 and Figure 2-4. Stamp out the proper mod level on the existing modification plate (mod level "" for RT-38A and mod level "2" for C-38A). 2.5 Part Number Decal (Mod Kit P/N 66A38- for RT- 38A and P/N 66A39- for C- 38A) Before placing part number decal, clean affected area (existing nameplate) with isopropyl alcohol. Remove backing from decal and place over the top portion of the existing nameplate. Ensure decal covers the unit name and old part number (456xx-). Do not cover serial number. See Figure 2-3 and Figure 2-4. Figure 2- Side view of control head after switch replacement. Page 8
2U57- MOD KIT Figure 2-2 Solder side view of A3A board. Figure 2-3 Part number and mod decals in installed positions, RT-38A. Serial number of unit should be visible under part number decal. Page 9
2U57- MOD KIT Figure 2-4 Part number and mod decals in installed positions, C-38A. Serial number of unit should be visible under part number decal. Page
2U57- MOD KIT SECTION III ILLUSTRATED PARTS IDENTIFICATION This section contains a schematic of the components in Sigma Tek's 2U57- kit. Also contained is the illustrated parts breakdown of this kit. Should it become necessary to order replacement parts for the 2U57- kit, contact SIGMA TEK, INC. at the address shown below. Please specify that the parts being ordered are for use on an ARC radio and give the radio model number and serial number SIGMA TEK, INC. ARC PART SALES DEPARTMENT INDUSTRIAL ROAD AUGUSTA, KANSAS 67 TEL. NO. -8-458-8977 OR 36-775-6373 TELEX NO. 9-74-6856 FAX. NO. 36-775-46 Page
2U57- MOD KIT Table 3-2U57- Modification Kit Fig-Item Part Number Qty Description 3-- 45659-2 Assembly, Switch 3--2 4479-243 IC, PROM 3--3 66A38- Part Number Decal, RT-38A 3--4 66A39- Part Number Decal, C-38A 3--5 66A43- Mod Decal, RT-38A 3--6 66A44- Mod Decal, C-38A Figure 3-. 2U57- Modification Kit Page 2
2U57- MOD KIT Figure 3-2 Modified schematic for A3A digital pc board assembly. Reference Figure 7-3 in the Service/Parts Manual Page 3