Sb: AMTOR MODS. FOR ICOM 720A

I PRESENT HERE AGAIN THE MODS FOR AMTOR OPERATION
FOR THE ICOM 720A TRANSCEIVER.
I RECEIVED THIS INFOS IN THE YEAR 1984-1985 !

ON MY ICOM 720A I DID THE FIRST SET OF MODS (BY G4ICM)
AND NOW MY ICOM 720A WORKS WELL IN AMTOR AND PACKET !

I HOPE THAT THIS INFOS ARE USEFUL FOR SOMEONE!

                              73 DE IK3BVD OP.ENRICO
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MODS FOR THE ICOM 720A:
THERE ARE 4 SETS OF MODS. SOME DUPLICATION WILL BE OBVIOUS.

BY G4ICM

MAIN BOARD:  CHANGE C40 C42 C43 C54 TO 0.1 MF
CHANGE C69 TO 0.01MF.

I.F. BOARD: C87 MAY BE 33MF, BUT SHOWN AS 0.0047MF, WHICH IS ON
PRINT SIDE.
CHANGE C87 TO 2.2MF, LEAVE 0.0047 ON PRINT SIDE.

R.F. BOARD: REMOVE C169 C127. CHANGE C165 TO 0.47MF.

NOISE BLANKER UPDATE. (CHECK IF DONE)
CHANGE C116 TO 10MF
CHANGE C171 TO 0.01MF

IF IN DIFFICULTIES CALL ENGLAND 2273 63859


BY KB9IS

DELETE C40 AND C43 ON MAIN UNIT

CHANGE C42 AND C43 (10MF AND 2.2MF) TO 1MF.

DISABLE A.F.MUTING- LINK SHORT-C69.

DELETE CAP. CT14 AT PIN 6 OF IC3 ON I.F. UNIT.

REARRANGE THE R9V TO TR Q22 ON I.F. UNIT
SO THAT IT IS CONNECTED TO UNSWITCHED "9VOLTS SUPPLY.

DO A SIMILAR MOD. TO THE "9 VOLT SUPPLY TO THE A.F. UNIT TO OVERCOME
SURGE PULSE.


GOOD LUCK DE " RON " GM3SAE


BY HB9XJ

MAIN UNIT: DELETE C40,C43
IF UNIT:   DELETE C87 AT PIN 6 OF IC 3
PICK UP AUDIO FROM ACCESSORY SOCKET (600 OHM)


BY PA3AXO

CONNECTIONS TO ACC. JACK ON THE BACK OF THE TANSCEIVER:

PIN 3 KEYLINE (NOTE THAT 200 MA CURRENT CAPABILITY IS REQUIRED
               SO A DIL RELAY MAY GIVE PROBLEMS)
PIN 4 AF TO CONVERTOR
PIN 9 FSK INPUT TTL LEVEL
PIN 8 GROUND

ON MAIN BOARD:REMOVE C40/42/43/54 AND REPLACE BY 0.1 UF
              REPLACE C69 BY 10 NF
ON RF BOARD  :REMOVE C169 AND 127 AND REPLACE C165 BY 0.68 UF
WHEN DESIRED THE RELAY TO CONTROL  AN EXTERNAL LINEAR AMP
CAN BE DISCONNECTED TO REDUCE THE CLICKING NOISES

GOOD LUCK AND BEST 73 DE JACK PA3AXO