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Icom IC-720A (IC 720 A IC720A) Amtor mods
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I present here again the mods for amtor operation
for the Icom IC-720A transceiver.
On my Icom IC-720A i did the first set of mods
and now my Icom IC-720A works well in amtor and packet !
I hope that this infos are useful for someone!
Mods for the Icom IC-720A:
There are 4 sets of mods. Some duplication will be obvious.
Main board:
Change C40 C42 C43 C54 to 0.1 uF
Change C69 TO 0.01uF.
I.F. Board:
C87 may be 33uF, but shown as 0.0047uF, which is on print side.
Change C87 to 2.2uF, leave 0.0047 on print side.
R.F. Board:
Remove C169 C127. Change C165 to 0.47uF.
Noise blanker update. (check if done)
Change C116 to 10uF
Change C171 to 0.01uF
If in difficulties call england 2273 63859
Delete C40 and C43 on main unit
Change C42 and C43 (10uF and 2.2uF) to 1uF.
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.
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
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