RECOMMENDED MODIFICATIONS TO AFMIT TERMINAL FOR AUX 12VDC POWER SUPPLY
THESE RECOMMENDATIONS ARE PROVIDED "AS-IS" WITHOUT WARRANTY OF ANY KIND. READ ENTIRE INSTRUCTIONS BEFORE PROCEEDING. DO NOT PROCEED UNLESS YOU FULLY UNDERSTAND THE PROCEDURES
DESCRIBED, AND AGREE WITH THEM.
1.0 PURPOSE
The most common AFMIT Terminal failure is associated with the auxiliary 12VDC power supply subsystem for powering the WEFAX
downconverter. The failure is usually a blown fuse, caused by either a shorted cable, or failed power supply. Occasionally,
the unregulated power supply fails when operated for extended periods on 50 Hz power. Diagnosing this problem can be
difficult in the field without a multimeter. In addition, once diagnosed, because the fuse is mounted on the internal
receiver boards, field replacement requires disassembling the AFMIT CPU and removing the power supply. By making some
simple and inexpensive modifications to the AFMIT CPU, the following improvements can be made:
1.1] Addition of red pilot light on side of AFMIT CPU instantly verifies intact fuse and power supply operation without
multimeter.
1.2] Addition of bulkhead panel fuseholder on side of AFMIT CPU makes field replacement of fuse a trivial operation.
1.3] Internal wiring of fuse cartridge to both the PC-GMS and PC-137 receivers allows both internal receivers to be powered
and fused from either 9-pin connector. Since only one receiver is ever used at any given time, this eliminates the
requirement to connect the 9-pin 12VDC connector to the 'correct' receiver; either one will power either receiver.
1.4] Replacing the unregulated 12VDC supply with a Universal switched and regulated 12VDC supply improves the survivability
of the auxiliary 12VDC supply when used on foreign power mains.
2.0 PARTS LIST FOR MODIFICATION
NOTE: RADIO SHACK PARTS ARE LISTED BECAUSE OF THEIR UNIVERSAL AVAILABILITY AT OR NEAR ALL US BASES. YOU MAY SUBSTITUTE AVAILABLE EQUIVALENT OR BETTER IF AVAILABLE.
2.1 QTY(1) BULKHEAD PANEL FUSEHOLDER FOR 5x20mm GLASS FUSE
RADIO SHACK #270-362 OR EQUIVALENT. EST PRICE: $1.59
2.2 QTY(1) 12V RED LENS LAMP,
RADIO SHACK #272-345 OR EQUIVALENT. EST PRICE: $1.49
2.3 QTY(1)LOT/5 SETS, SNAPCONNECTORS FOR INTERNAL WIRING
RADIO SHACK #64-3085 OR EQUIVALENT. EST PRICE: $1.49
2.4 QTY(1) LOT 18G HOOKUP WIRE, STRANDED
RADIO SHACK #278-1226 OR EQUIVALENT. EST PRICE: $4.49
2.5 QTY(1) 180 OHM 1/2 WATT CARBON FILM RESISTOR
RADIO SHACK #271-1110 OR EQUIVALENT. EST PRICE: $0.49
==================
SUBTOTAL: $9.58
OPTIONAL POWER SUPPLY UPGRADE:
2.6 QTY(1) UNIVERSAL SWITCHING 12VDC REGULATED POWER SUPPLY
MOUSER ELECTRONICS PN# 552-PSA-30U-120
PHIHONG 12VDC 2.5A 30W UNIV INPUT
(TELEPHONE: 1-800-346-6873)
EST PRICE: $41.60
2.7 QTY(1) CEE/IEC-320 3-WIRE POWER CORD FOR POWER SUPPLY
RADIO SHACK #278-1257(FOR US NEMA 5-15P)
OR AS REQUIRED BY LOCAL MAINS. EST PRICE: $3.99
2.8 QTY(1) D-SUB 9-PIN CONNECTOR (MALE)
RADIO SHACK #276-1537 OR EQUIVALENT. EST PRICE: $0.99
2.9 QTY(1) D-SUB HOOD FOR 9-PIN CONNECTOR
RADIO SHACK #276-1539 OR EQUIVALENT. EST PRICE: $0.99
==================
SUBTOTAL: $47.57
TOTAL PARTS: $57.15
MISC: MULTIMETER, SOLDER, SOLDERING IRON, DRILL & DRILL BITS OR CHASSIS PUNCH TO MODIFY CPU CASE.
3.0 INTERNAL RE-WIRING PROCEDURE
GENERAL: USE ANTI-STATIC PRECAUTIONS WHEN DISASSEMBLING CPU AND HANDLING ADAPTERS. PERFORM AT GROUNDED WORKSTATION WITH
ANTI-STATIC MAT/WRIST STRAP IF POSSIBLE. MINOR DRILLING MUST BE PERFORMED ON CPU CASE. BE SURE TO ORIENT CASE AND SHIELD
INTERIOR FROM METAL SHAVINGS DURING DRILLING OPERATION. DRILL AFTER REMOVING INTERNAL ADAPTER CARDS. IF POSSIBLE, CAREFULLY
VACCUUM WHILE DRILLING TO AVOID DISPERSING METAL SHAVINGS INSIDE CPU CASE. NOTE THAT VACCUUM CAN GENERATE EXCESSIVE STATIC
DISCHARGE; GROUND VACCUUM NOZZLE IF POSSIBLE. GROUND CASE WHILE DRILLING.
3.1] STEP 1: DISASSEMBLE AFMIT CPU TO REMOVE ADAPTER CARDS PER INSTRUCTIONS IN BACK OF WEATHERTRAC MANUAL. IN ADDITION TO
RECEIVERS, REMOVE VGA AND MULTI-FUNCTION CARD. NOTE LOCATION OF ALL CABLES BEFORE REMOVING ADAPTERS.
3.2] STEP 2: READ THIS STEP CAREFULLY BEFORE DRILLING. NOTE ROWS OF EXISTING HOLES ON SIDE OF AFMIT CPU ABOVE ADAPTER CARD
RAILS, ON SIDE OF TERMINAL ON WHICH RECEIVERS ARE FOUND. NOTE INTERFERENCE WITH POWER SUPPLY ON TOP ROWS OF HOLES, ACCESS
TO ADAPTER CARDS ON LOWER ROWS. NOTE EXPOSURE OF HOLES WHEN PLASTIC CASE IS INSTALLED. ONE OF THESE HOLES WILL BE ENLARGED
TO ACCEPT THE FUSE CARTRIDGE. IT SHOULD BE ONE OF THE LOWER HOLES, CLOSEST TO THE MULTI-FUNCTION ADAPTER CARD, SO AS NOT TO
INTERFERE WITH THE RECEIVER CARDS OR VGA ADAPTER. (WHEN ASSEMBLED, THIS MAY MEAN THAT THE MULTI-FUNCTION CARD CANNOT BE
REMOVED WITHOUT FIRST REMOVING THE FUSE CARTRIDGE.) WHEN THE PLASTIC CASE AND ALL ADAPTERS ARE REINSTALLED, THE NEW FUSE
CARTRIDGE AND PILOT LIGHT SHOULD BE VISIBLE. AFTER CAREFULLY SELECTING AND CHECKING THE LOCATION OF THIS HOLE, PROCEED TO
STEP 3.
3.3] STEP 3: IF AN APPROPRIATE CHASSIS PUNCH IS NOT AVAILABLE(LIKELY)SELECT A DRILL BIT TO ACCEPT THE FUSEHOLDER BODY, AND
ENLARGE THE CAREFULLY SELECTED HOLE, BEING CAREFUL NOT TO SHED METAL SHAVINGS INTO THE CPU CASE. (TURNING THE CASE ON ITS
SIDE/UPSIDE DOWN, SO SHAVINGS DON'T FALL INSIDE CASE.)
3.4]STEP 4: THE 12V RED LENS LAMP WILL REQUIRE THAT A NEW 7/32" HOLE BE DRILLED IN THE CASE, IN OR NEAR THE LOCATION OF THE
FUSEHOLDER. SELECT A LOCATION THAT IS FAR ENOUGH AWAY SO THAT THE FUSEHOLDER AND LAMP BODIES WILL NOT INTERFERE WITH EACH
OTHER WHEN ASSEMBLED. ALSO PICK A LOCATION THAT WILL NOT INTERFERE WITH ADAPTER ASSEMBLY. CAREFULLY DRILL THE LAMP HOLE, AS
BEFORE.
3.5] STEP 5: BLOW OUT CPU CASE TO MAKE SURE METAL SHAVINGS HAVE NOT BEEN DISPERSED INSIDE CASE.
3.6] STEP 6: REINSERT MULTI-FUNCTION CARD AND CABLES.
3.7] STEP 7: PREPARE FUSE LEADS ON PC-137 AND PC-GMS RECEIVER CARDS. THE PROCEDURE FOR THIS WILL DEPEND UPON THE TYPE OF
FUSE ON THE RECEIVER CARD:
3.7.1] IF THE RECEIVER CARD HAS A 5x20MM FUSE CARTRIDGE:
REMOVE THE FUSE FROM THE CARTRIDGE. PREPARE TWO 12" LENGTHS OF 18 GAGE HOOKUP WIRE. USE TWO COLORS IF AVAILABLE. EACH WILL
BE SOLDERED TO A SEPARATE SIDE OF THE FUSE CARTRIDGE. ONE SIDE OF THE FUSE CARTRIDGE IS CONNECTED TO PIN 1 OF THE 9-PIN
CONNECTOR. THIS IS THE POWER LEAD-IN. THE OTHER SIDE IS CONNECTED TO THE CENTER-PIN OF THE BNC VIA A DC INSERTION CIRCUIT
(CAPACITOR TO GROUND AND INDUCTOR IN-LINE). VERIFY CONTINUITY OF EACH USING A MULTIMETER. ALTERNATELY, SOLDER THE LEADS TO
BOTH SIDES OF A "BLOWN" FUSE; THIS HAS THE ADVANTAGE OF NOT PERMENANTLY MODIFYING THE ADAPTERS. IF YOU USE THIS METHOD,
NOTE THAT THE LOWER LEAD(NEAR THE CARD EDGE)IS THE POWER LEAD-IN. NOTE ALSO THAT, WHEN SOLDERING THE LEAD ONTO THE 5x20mm
GLASS CARTRIDGE, THE GLUE WILL TEMPORARILY MELT, CAUSING THE METAL CAP TO WANT TO "SLIDE" OFF THE GLASS; APPLY LIGHT
PRESSURE UNTIL THE FUSE COOLS AND THE GLUE RE-HARDENS.
3.7.2] IF THE RECEIVER CARD HAS A SMALL GREEN PICO FUSE SOLDERED ON THE BOARD:
YOU WILL NEED TO REMOVE AND DESOLDER THE FUSE, LEAVING TWO CLEAN HOLES IN WHICH THE NEW LEADS WILL BE DIRECTLY RESOLDERED.
PREPARE TWO 12" LENGTHS OF 18 GAGE HOOKUP WIRE. STRIP ABOUT .25" OF INSULATION, TIN THE ENDS, AND TRIM. USE TWO COLORS IF
AVAILABLE. EACH WILL BE SOLDERED TO ONE OF THE FUSE HOLES. ONE OF THE FUSE HOLES IS CONNECTED TO PIN 1 OF THE 9-PIN
CONNECTOR. THIS IS THE POWER LEAD-IN. THE OTHER HOLE IS CONNECTED TO THE CENTER-PIN OF THE BNC VIA A DC INSERTION CIRCUIT
(CAPACITOR TO GROUND AND INDUCTOR IN-LINE). VERIFY CONTINUITY OF EACH USING A MULTIMETER.
3.8] STEP 8: ON THE OTHER END OF THE VERIFIED POWER-LEAD-IN, SOLDER(DO NOT CRIMP)A FEMALE SNAPCONNECTOR. YOU WILL NEED TO
TEMPORARILY PRESS THE PLASTIC SHIELD OFF OF THE METAL CONNECTOR TO SOLDER THE LEAD. ON THE OTHER LEAD, SOLDER A MALE
SNAPCONNECTOR. DO THIS FOR BOTH THE PC-GMS AND PC-137 RECEIVERS. YOU SHOULD NOW HAVE 2 LEADS COMING FROM EACH RECIEVER, ONE
FROM EACH POWER-LEAD HAVING A FEMALE SNAP CONNECTOR, AND ONE FROM EACH DC INSERTION LEAD HAVING A MALE SNAP CONNECTOR.
3.9] STEP 9: PREPARE TWO 6" LEADS USING THE SAME COLOR AS THE POWER-LEAD IN, AND TWO 8" LEADS USING THE SAME COLOR AS THE
DC INSERTION LEADS. ON THE 6" POWER-LEADS, SOLDER(DO NOT CRIMP)MALE SNAP CONNECTORS. ON THE 8" DC-INSERTION LEADS, SOLDER
FEMALE SNAP CONNECTORS. THESE ARE THE MATES FOR THE LEADS FROM THE RECEIVERS, AND SHOULD MATCH COLORS AND MATE GENDERS.
3.10] STEP 10: PREPARE TWO SHORT LEADS (3") TO CONNECT THE LAMP TO THE SIDE TAB OF THE FUSEHOLDER AND CASE GROUND VIA 180
OHM RESISTOR BY TINNING BOTH ENDS OF THE SHORT LEADS. SOLDER ONE END OF ONE LEAD TO THE 180 OHM RESISTOR. SOLDER OTHER END
OF 180 OHM RESISTOR TO LAMP LOCK WASHER. (THIS WILL GROUND TO CASE WHEN LAMP IS ASSEMBLED.) DO NOT SOLDER TO THE
LAMP/FUSEHOLDER YET. NOTE: 180 OHM RESISTOR IS OPTIONAL. THIS WILL REDUCE CURRENT DRAW/INTENSITY FROM ABOUT 60 mA TO ABOUT
40 mA, AND WILL CURRENT LIMIT DRAIN SHOULD LAMP SHORT.
3.11] STEP 11: ASSEMBLE FUSEHOLDER INTO CASE. TIGHTEN.
3.12] STEP 12: ASSEMBLE LAMP WITH GROUND LEAD/LOCKWASHER INTO CASE. TIGHTEN.
3.13] STEP 13: SOLDER GROUND LEAD/RESISTOR TO ONE SIDE OF LAMP.
3.14] STEP 14: SOLDER TWO 8" DC INSERTION LEADS AND OTHER STEP 10 SHORT LEAD(WITHOUT RESISTOR) TO FUSEHOLDER SIDE TAB.
3.15] STEP 15: SOLDER TWO 6" POWER LEADS TO CENTER TAB ON FUSEHOLDER.
3.16] STEP 16: REINSTALL RECEIVER'S/ADAPTERS. CONNECT COLOR CODED/GENDER MATCHED LEADS FROM RECEIVERS TO FUSEHOLDER USING
MATING SNAP CONNECTORS. TIDY-UP LOOSE LEADS.
3.17] STEP 17: WITH 5x20mm 1A FUSE INSTALLED, VERIFY CONTINUITY USING MULTIMETER BETWEEN THE FOLLOWING:
DB9 PIN 1 AND BNC CENTER PIN.
DB9 PIN 1 AND DB9 PIN 1 ON EACH RECEIVER.
3.18] STEP 18: CONNECT 12VDC POWER TO EITHER DB-9 CONNECTOR. VERIFY RED LAMP IS ON. (WITHOUT 180 OHM RESISTER, LAMP
BRIGHTNESS WILL BE MORE INTENSE.) VERIFY 12VDC ON UHF BNC CENTER PINS ON BOTH PC-GMS AND PC-137 RECEIVERS.
3.19] STEP 19: WITH 12VDC POWER CONNECTED, REMOVE 1A FUSE FROM FUSEHOLDER. VERIFY RED LAMP IS OFF AND 12VDC POWER REMOVED
FROM UHF BNC ON BOTH PC-GMS AND PC-137 RECEIVERS.
3.20] STEP 20: RE-ASSEMBLE AFMIT TERMINAL.
4.0] OPTIONAL 12VDC POWER SUPPLY REPLACEMENT
A DB-9 PIN MALE CONNECTOR MUST BE ASSEMBLED TO THE NEW POWER SUPPLY. THE (+)LEAD MUST BE CONNECTED TO PIN 1, AND THE
(-/GROUND)LEAD TO PIN 6. BE CAREFUL TO SELECT THE CORRECT LEAD. DO NOT REVERSE POLARITY.
4.1] STEP 1: CUT THE COAX POWER CONNECTOR OFF OF THE POWER SUPPLY, 1/2" FROM THE COAX CONNECTOR.
4.2] STEP 2: USING THE SHORT COAX CONNECTOR JUST REMOVED, VERIFY WHICH OF THE TWO LEADS IS CONNECTED TO THE CENTER OF THE
COAX. THIS IS THE (+) POWER LEAD. THE WIRE WILL EITHER BE MARKED OR UNMARKED. NOTE WHICH ONE IS THE (+) LEAD. THROW AWAY
THE SHORT COAX CONNECTOR.
4.3] STEP 3: PREPARE THE LONG LEADS ON THE POWER SUPPLY. TRIM APPROX 0.25" OFF EACH LEAD, AND TIN WITH SOLDER.
4.4] STEP 4: SOLDER THE (+) LEAD TO PIN 1 OF THE DB-9 CONNECTOR. SOLDER SHOULD FLOW INTO SOLDER CUP. AVOID COLD SOLDER
JOINTS.
4.5] STEP 5: SOLDER THE (-) LEAD TO PIN 6 OF THE DB-9 CONNECTOR, DIRECTLY BELOW PIN-1.
4.6] STEP 6: VERIFY NO SHORT BETWEEN PIN 1 AND PIN 6 OR ANY OTHER PINS.
4.7] STEP 7: ASSEMBLE DB-9 SHELL TO DB-9 CONNECTOR.
4.8] STEP 8: CONNECT 3-WIRE CEE/IEC 320 GROUNDED POWER CORD FOR LOCAL MAINS.
REPLACEMENT POWER SUPPLY PROVIDES REGULATED +/- 5% 12VDC OUTPUT OVER 0-2.5 AMPS FROM UNIVERSAL INPUT (90-264 VAC, 47-63 HZ)
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