From    : G1YYH @ G1YYH.GB7CRG.NW.GBR.EU
To      : MODS @ GBR
Date    : 891214/2038
Msgid   : BF 206@G1YYH, 14568@GB7YHF $THX5AT.PT3
Subject : Kenwood TH-x5at Mods - 3/4
Path    : GB7YAX!GB7CHS!GB7CRG!G1YYH


Here is the function of the diodes and pull up or pull down
resistors (for both the TH-25AT and the TH-45AT unless otherwise
specified):

D4selects the display type.
installed:channel display
removed:normal frequency display

You probably don't want to install this.

R6 is the pullup resistor for D4.  Do not remove it, so that
if D4 is removed, pin 44 of IC2 will be properly pulled up.

D3selects VHF or UHF.
installed:VHF
removed:UHF

You definitely don't want to change this!

R7 is the pullup resistor for D3.  Do not remove it, so that
if D3 is removed, pin 45 of IC2 will be properly pulled up.

R25selects automatic offset selection.
installed:automatic offset selection enabled.
removed:automatic offset selection disabled.

R25 seems to have no effect on the TH-45AT.

R23,27frequency selection step size.

Frequency selection step sizes is only known for TH-45AT.

R23R27frequency selection step sizes:
--------------- --------- ---- ------
outout 5 and 10   kHz
inout 5 and 25   kHz (TH-45AT default)
outin 5 and 12.5 kHz (author's preference)
inin10 and 20   kHz

R23 probably has no effect on the TH-25AT.  I never checked.
I was quite satisfied with the 5 and 10 kHz step sizes for
the TH-25AT.  I never tried changing R27 to see what would
happen.

R24? something with the CTCSS tone ?
installed:When a TX offset is selected, the CTCSS tone
is always transmitted.  The TONE button does
not work correctly.  When the TONE button is
depressed, the display goes to 430.000 c, and
nothing seems to work.  (A "c" is displayed
in the channel number position.)  The action
of the TH-25AT is unknown.
removed:CTCSS tone selection works correctly.  Both
the TH-25AT and the TH-45AT are delivered
this way.

You probably don't want to install this.

R19function unknown.
R19 is not installed in the European version.

R20function unknown.
R20 is not installed in the European version.

R21function unknown.
R21 is not installed in the European version.

R19, R20, and R21 are all in parallel.  Thus, if any of them
is installed, it is like all of them are installed.

R26function unknown.
R26 is installed in the European version.

On the TH-25AT:

R22,28select RX and TX frequency range.

R22R28RX rangeTX range
-------- ------- -----
inout144-148141-163(USA default)
inin144-148144-148
outout100-200100-200(only where
your PLL
locks up.)
outin142-151???-???