Modifications for the Kenwood TM-221
General Coverage XMIT - TM-221/A
Remove top and bottom covers, remove locking ring on mic connector.
Carefully remove plastic cover.
Pull front of radio off (plug in connector)
Locate the control unit (xx53-3040-xx)
Remove the small resistor chip from r25, this gives you xmit from
(142.000 thru 151.995)
Replace the same resistor chip from last step on to the same board
at r24 which is empty, this gives you xmit from (138.000 thru 154.000)
Each set will give diffrent range depending on the vco setting, some
Well xmit higher than 154.000 and some will shut off lower. This
can be changed by resetting the vco.
TM-221A Final Module Hints
When the Final module is replaced in a TM-221A, there is a
possiblity that the transmit power will not go higher than
47 watts, even witht he APC turned OFF. This is due to
variances in input impedance of Final Modules. To correct
this condition, an 8 pF capacitor can be added between the
input of the module and ground. With some modules, a value
between 8 pF and 15 pF will be required. Try to choose a
value as close to 8 pF as possible to prevent oscillation.
The capacitor should be designated as C19 on the Final Unit
8pF Ceramic Capacitor Part # CC45CH1H080D
This modification may be performed under warranty.
Turn the APC off (TX-RX unit VR-6: Clockwise).
Adjust TC3 TC4 (TX-RX) for maximum power supply current.
Since the APC is off, the Final will produce very high
power output. It is important to perform this step as
quickly as possible.
Adjust the APC for 45 Watts.
Time required for this modification is 0.25 hrs or less.
TM-221A No TX in High Power Due to Voltage Drop
Some TM-221A transceivers may intermittently not transmit in
the high power mode. This condition may be the result of a
voltage drop at the fuse terminals on the power cord. To
prevent a voltage drop, solder the terminals by following
the procedure below.
This modification may be covered under warranty.
Disconnect the antenna and power supply.
Open and remove the plastic fuse holder.
Remove the fuse from the terminals.
Flow solder between the terminals and the exposed
strands of the cable.
Allow the terminals to cool and then reinstall the
fuse and close the holder.
Time required for this modification is 0.24 hrs or less.
The get your 221A to recieve from 138-174 Mhz you need to remove the front panel and gain access to the chip resistors and re-arrange them as follows:
R22 R23 R24 R25
X O O X X = Connected
O = Left out
If you are running a vk version removal of R24 is all that is needed. The TX will remain at 144-148 Mhz even after the mod.
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