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Icom IC- 3200A mods
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IC3200A.4
IC-3200A TX to RX DELAY FIX
FOR THOSE POOR SOULS WHO ARE TRYING TO USE THE IC-3200A ON PACKET HERE IS
HERE IS SOME RELIEF.
THE PROBLEM IS THAT WHEN GOING FROM TRANSMIT TO RECEIVE THERE IS A DELAY
IN THE RECEIVE AUDIO TURN ON, WHICH IS ON THE ORDER OF 500 MILLISECONDS
AND MAY BE TOO LONG FOR SOME PACKET SITUATIONS UNLESS EVERYONE HAD THEIR
TXDELAY SET TO 750 MILLISECONDS.
THERE ARE TWO WAYS TO RESOLVE THE PROBLEM. BOTH ARE FAIRLEY SIMPLE.
THE EASIEST WAY IS TO REMOVE THE MUTING ON THE AUDIO P.A. I.C.
THE INSTRUCTIONS FOLLOW:
1. REMOVE THE COVER THAT HAS THE SPEAKER ATTACHED TO IT
(BEING CAREFUL OF THE WIRES)
2. WITH THE FRONT OF THE RADIO FACING YOU, LOOK FOR THE
AUDIO P.A. I.C. IN THE RIGHT REAR PART OF THE RADIO NEXT TO
THE CHASSIS IT IS MARKED "UPC2002", LOOKS LIKE A TO-220
CASE TRANSISTOR, AND HAS FIVE LEADS ON IT
3. IMMEDIATELY TO THE LEFT OF THE "UPC2002" IS A DIODE STANDING
ON END, AND MARKED "D19" ON THE CIRCUIT BOARD THIS IS THE
DIODE THAT MUTES THE AUDIO P.A. I.C. DURING TRANSMIT
4. CUT ONE LEG OF "D19" AND THE AUDIO P.A. I.C. WILL NO LONGER
BE MUTED DURING TRANSMIT AND THE RECEIVER WILL RESPOND ALMOST
IMMEDIATELY.
THIS IS ALL THAT IS REQ'D AND MY TESTS HAVE SHOWN THAT THE IC-3200A WILL
WORK WITH OTHER TNC'S WITH TXDELAY'S SET AS SHORT AS 150 MSECS WHERE
BEFORE THIS MODIFICATION A TXDELAY OF ABOUT 600 MSECS WAS REQUIRED
OF THE STATION TRYING TO COMMUNICATE TO THE IC-3200A.
FOR THOSE INTERESTED IN AN ALTERNATE METHOD HERE IS WHAT HAS BEEN DONE BY
WB4FOW ON SEVERAL OTHER RADIOS:
SINCE ABOUT 1985 MOST ICOM RADIOS HAVE PIN 8 OF THE MICROPHONE CONNECTOR
WIRED TO THE SPEAKER. THIS IS CONVENIENT FOR THE WIRING OF A TNC
AND IS USUALLY EASY TO MODIFY SO THAT RECEIVE AUDIO IS TAKEN FROM
THE HIGH SIDE OF THE VOLUME CONTROL.
CONTINUED IN IC3200A.5
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