[Kenwood] RE: Request for info on TS-850 Tuner

[Randy Brothers]

Scott,

The mod is on the Yahoo TS-850/450/690 group, with photos.

73,
Randy
K9OR
--------------------------------------------
Text from VE3TMT:

Kenwood TS850S Tuner Mod Theory & Procedure.

The basis for the mod is quite simple.  When a received signal enters =
the
850=20
through the antenna connector it is routed through a small relay to the =
RF
board=20
where the receive signal chain begins, completely bypassing the internal
antenna=20
tuner.  Under transmit conditions the 100W signal is routed from the =
final
TX=20
amplifier on to the low pass filter board.  From here it is sent through =
the
antenna=20
tuner and then to the TX side of that same small relay and out to the
antenna. =20
This relay is located on a small LP filter sub-board  directly below the
antenna connector. =20
The simple solution to performing this mod is to move the position of =
the
tuner in the chain=20
from the TX only side to both the TX/RX side and the only place to do =
this
is between the=20
antenna connector and the TX/RX relay.

You will need one length of coaxial cable with a plug similar to the =
ones
that connect the=20
LP filter to the antenna tuner.  If you don't plan on using a station
monitor with your 850=20
you can "borrow" the cable used for that purpose. You do however have to
unsolder or=20
cut one end of this cable from the RF board on the bottom side of the =
radio.
If you plan=20
on using this method do the following:

Remove the bottom cover of the radio.  With the front of the radio =
facing
you, the RF=20
board is on the left.  Remove the 4 screws that hold the shield plate.  =
This
is the shiny=20
cover at the back of the board.  Look towards the rear right corner of =
the
board and you=20
will see a coaxial cable soldered to the board.  It is the only one =
there.
Just to verify,=20
follow the cable, the other end should plug into CN26 around the middle =
of
the RF board. =20
Either cut or unsolder the end near the rear of the radio. Save this =
cable
and set it aside for now.

Turn the radio back over, with the front facing you.  Looking to the =
rear,
directly under the=20
antenna connector you will see the small filter sub-board.  This is the
board we will be working=20
on.  Note the 2 coaxial cables on this board.  The one on the left is =
the
receive signal out, the=20
one on the right is the RF output from the antenna tuner.  Remove these =
2
cables from the board. =20
Unplug the small wire harness.  Unsolder the small wire and ground from =
the
antenna connecter=20
itself.  Remove the 2 screws and pull the board out.

Unsolder the small wire on the sub-board that went to the antenna =
connector.

Taking the "borrowed" cable from the RF board, strip and tin the cut =
end.
Solder the tinned=20
center conductor into the hole where the small wire came out of.  That =
is
all the work that=20
needs to be done on this board.  Reverse the disassembly steps above and =
put
it back in place.

Using the red banded cable from the tuner, it will now be used as a =
jumper
from the=20
LP filter board to the filter sub-board where the antenna tuner out was
connected. =20
Take the remaining cable and cut one end and prepare for soldering as =
you
did with=20
the first cable.  This cable will be soldered from the antenna connector
itself.  Plug the=20
other end into the TUN OUT jack on the antenna tuner board.  The cable
soldered to=20
the filter sub-board plugs in to the TUN IN jack on the tuner board.  =
Check
all your wiring=20
and replace the filter board cover and top cover off the radio.  Don't
forget to plug the internal
speaker back in first!!

To verify it is working, do the following:

Tune to WWV on 5, 10 or 15 Mhz.  Make sure the tuner function is off =
first.

Note the signal reading.  Tune slightly off frequency, then engage the
tuner. =20
After the tuner matches the antenna, tune back to WWV and compare signal
levels. =20
Unless you are using a perfectly resonant antenna to begin with, you =
should
see a=20
higher signal strength with the tuner engaged.  Take the tuner out of =
line
and the=20
signal should drop.

That's all there is to it.  Sorry about the quality of some of the =
pictures,
but the=20
digital camera is only a cheap one.  If you have any questions please =
e-mail
me=20
direct and I will try and answer them.

73,
Max  ve3tmt@yahoo.ca