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[CQ-Contest] TS-850 contest mods (long)

Subject: [CQ-Contest] TS-850 contest mods (long)
From: k6ll@juno.com (David O Hachadorian)
Date: Tue Jun 3 23:22:00 1997
There was a huge number of requests for the TS-850 mods, so
I'll just post them here.


BY: N7EX (ex-N0DH), Dave Henderson

One of the minor draw backs to the TS-850 as a CW contest machine is the
inability to use the internal keyer in conjunction with an external
keying circuit such as a personal computer or auxiliary memory keyer. As
designed you must manually throw a switch from internal to external
keying to switch between one or the other. To make matters even more
inconvenient this switch is on the back of the unit and is not readily
accessible during normal operation. 

Simply said this modification involves running a new keying line from
the junction of S1 and D51 on the IF Board. For convenience this
additional keying line can be wired to the DSP1 and/or DSP2 RCA  phono
jacks if you do not use the external DSP unit.

The modification to the unit to resolve this problem takes less than 30
minutes to accomplish and can be done without "permanently" modifying
the unit which would detract from its future resale value. If you don't
use the external DSP unit then the two RCA phono jacks marked DSP1 and
DSP2 can be used as additional keying input jacks as will be outlined
below. If you use the external DSP unit then the modification can still
be accomplished by running the external keying line out on a "pigtail".
I highly recommend the purchase of a service manual which will greatly
improve your  ability to indentify the circuit points involved in the
modification.  Considering that the radio costs $1500 what's another $30
to keep from messing it up! By the way compared to the two TS-930's that
I nursed through the 80's, this radio is a breeze to trouble shoot and
repair which I have had to do twice through no fault of Kenwood  (long
stupid story ~8>).

>From here you proceed at your own risk, if you fry the radio DON'T CALL
ME. A precision low wattage solder pencil for doing surface mount
soldering is recommended, If all you have is a 150 watt Weller solder
gun then read no farther your better off taking the unit to an expert
rather than "melt" the circuit traces.

I assume no risk for the accuracy or completeness of the enclosed
information. All yee who enter here embrace all hope for you may likely
have a better contest radio when you are done.

1) Turn the unit upside down with the back of the TS-850 toward you.

2) Remove the bottom cover.

3) In this position the IF board is on your left.

4) Remove all the screws holding the IF board to the chassis.(put them
in a jar or something for safe keeping).

5) Unplug enough of the cabling to allow you to tilt the board up so
that you can access the bottom side of the board underneath S1 the
"External/Internal" keying switch.

6) On the bottom side of the board directly underneath S1 you will see 6
solder pads arranged in two rows of three pads each.

7) The middle pad on S1 nearest the back of the radio should be GROUND,
solder the braid of an approximately 9 inch piece of small audio style
shielded cable to this point, being careful to dress the coax so as not
to short  to  other circuitry.

8) The middle pad on S1 in the next row up of three pads is the keying
line. Solder the center of the shielded cable to this point.

9) Route the other end of the shielded audio cable   through the chassis
in the vicinity of the DSP jacks above.

10) Carefully inspect all solder joints for shorts, etc. Replug the wire
harnesses unplugged in step 5 above and reassemble the board to housing.
Reassemble the bottom cover.

11) Turn the unit over and remove the top cover. 

12) Find the DSP input board with the three RCA phono jacks on it at the
rear of the unit. The two DSP jacks are on the right when facing the
rear of the unit. There are two connectors on this board (a 2pin and a
4pin). Unplug the 4 pin connector. Obtain another 4 pin connector and
connect as follows (or directly solder to the underside of the board as
follows) If you only need one additional CW jack then ground is pin 2
(closer to center of the radio)connect the braid of your new key line to
this pin. The input from the middle RCA phono plug is pin 1 connect the
ceneter conductor to this pin. Like wise if you want two additional CW
jacks then do as above plus add a short between pins 1 and 3. If you
want a small RF choke or some ferrite beads on the center conductor of
the audio cable may prevent keying problems in high RF field

14)Close the unit up and switch S1 to INTERNAL keying. You should now be
able to key the unit via the internal keyer (Via the standard key input
jack) or with an external keyer or computer via the old DSP jacks,
without having to switch S1!

TS-850 front panel cw sidetone level adjustment mod by
N6TR. Refer to NCJ, Vol 22, Issue 2, Page 23.

TS-850 Separate Receive Antenna Modification #1.
This modification was developed by Brian WA3WJD

Make a short loop of white telfon cable with a male and female BNC

Loop it out of the back of the rig so just enough of the coax sticks
out so the BNCs can be joined with a barrel connector.

Locate the little header connector on the filter board in the TS-850 that
on the receiver side of the TS850 antenna relay.  Pull that connector

Spend a little time tracking down male and female header connectors
that match what Kenwood uses.  Install those on the ends of the white
teflon coaxes sticking in the back of the radio.

For normal use, just connect the BNCs with a barrel connector and the rig
is normal.  For Beverage use, connect an extra antenna switch common and
ant #1 to the BNC connectors, and put ur Beverages on the other


TS-850 Separate RX antenna input mod #2.
This mod was developed by N6TR.

This is near the top of everyone's list when they are asked "What things
bug you about the TS-850S".  I initially overcame this deficiency by 
modifying my amplifier so I could connect a different receive antenna
to the TR relay.  However, I wanted to change things so there wasn't as 
much RF getting into the RX antenna due to close proximity to the 
amplifier's output.  This became a problem when using the same receive
antenna on a second radio (you know two radio operating was going to work
its way in here somehow).

Ville, OH2MM had provided me with instruction on how he modified his
TS-850S to have a separate RX input and this inspired me to try it.
Here are some simple steps to hopefully inspire others:

It took me an unrushed two hours to do all this.

1. Remove the top panel (you don't need to take off the bottom one.

2. Remove the plate which sits between the fan and the back of the
radio.  This covers the output filter PC board.

3. Unsolder the connections to the SO-239 output connector.

4. Remove the three cables from the PC board next to the SO-239.  This
includes two coax and one 3 conductor harness.

5. Remove the two screws holding in the PC board and remove it.

6. Locate the trace that goes from the relay's normally closed contact.
You can use an ohm-meter to find it - probe from the wire that went to
SO-239.  You will find a short trace on the back of the board which runs
to a chip capacitor.  Cut this trace and solder some very small coax
to each side of the cut - connect ground to the nearby ground trace.

Make the cables about 4 inches long.

7. Remove the antenna tuner. There are 2 screws in the back and front
will need a magnetic screw-driver) and one on the side.  You will need to
carefully unplug two wire harnesses and one coax connector.

8. Drill two holes for phono jacks on the back of the radio.  Be careful
not to obstruct the screw hole for one of the screws in the back of the 
antenna tuner.  The best place is between the RF output connector and 
the groundpost.  Put them on top of each other and as close to the bump
on the back panel as possible.  I used a vacuum cleaner while drilling to

make sure no metal chips went anywhere.

9. You will find a small hole under the SO-239 where you can feed
the two coaxs through.  Solder them to the phono jacks and reassemble
everything.  I put back to back diodes on the RX antennas input, but
you may not want to do this.  A better thing would be to add a relay to
disconnect the RX antenna input when transmitting.  I took care of 
that in project #2.

10.  Obviously, you will need a jumper cable to make your receiver 
work again.

PROJECT #2 - The switch box:

Parts list - 4 position rotary switch
             DPDT 12 VDC relay
             1 K Ohm pot (optional)
             12 phono jacks (or you can get by with 9)
             mini box for above and knobs.
             Clamp diode for relay coil if not included in relay

This box does two things: disconnects the receive antenna input when 
transmitting and allows selection of the transmitting antenna or one
of three RX antennas when receiving.  The pot can be used for RF 
attenuation if your rig doesn't have one.

The relay gets controlled by the PTT output from your rig that normally
would go to your amplifier.  Then one set of the contacts is used to 
key your amplifier.  Don't forget to put a diode across the coil of
your relay if there isn't one internally.  Otherwise, you will have 
undesired arcing across the contacts of the relay in your radio.

The other set of contacts disconnect the output of the rotary swtich
when transmitting.  The rotary switch selects either the signal
coming from the transmitting antenna (from the TR relay in your rig)
or one of three receiving antennas.  I use two phono jacks per RX
antenna so I can feed them to other boxes for other radios.  I also
use two jacks for +12 volts so I can jumper power to another box.

You can build up one of these boxes in an hour or two.  You can epoxy
the relay to the mini box.

If you want the pot there to act as an attenuator, I just hook it
up like you would a volume control:  one end is ground, the other end 
goes to the output of the rotary switch and the wiper goes to the 
output.  Use shielded cable as much as possible to avoid stray 
Computer Interface for the TS-850, without using the IF-232
Level Converter. Mod developed by N6TR and possibly others,
with zener idea added by K6LL.

                    470 ohms
DB9 PIN 3 (TXD)>----/\/\/\/\------------<TS850 ACC 1 PIN 3 (RXD)
(DB25 PIN 2)                   |
                              ---- 5 VOLT ZENER DIODE
                              /  \
DB9 PIN 5 (GND)>------------------------<TS850 ACC 1 PIN 1 (GND)
(DB25 PIN 7)

DB9 PIN 2 (RXD)>------------------------<TS850 ACC 1 PIN 2 (TXD)
(DB25 PIN 3)

                                   -----<TS850 ACC 1 PIN 4 (CTS)
                                   -----<TS850 ACC 1 PIN 5 (RTS)

TS-850 Power Output Control - VR7 on the RF Board (bottom side
of radio). 125 watts or so on cw is safe. Do not exceed 100 watts
on SSB, since distortion will broaden the transmitted signal.
TS-850 Level Attenuator for DRU-2 playback audio. Mod by

1. Remove the little hatch on the top of the radio.
2. With the front of the radio facing you, find connector
   CN505. It is a five pin connector near the filter
   DIP switches. The white wire on the leftmost terminal
   carries the DRU audio output.
3. Cut the white wire and insert a 100K ohm micromini pot,
   shunted with a 220 pf capacitor. Adjust the pot until
   DRU playback level matches live microphone level.

Dave Hachadorian, K6LL

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