Modifications for the Kenwood TS-850

TS-850S observations

Observations of KC2CT

Having lived with Kenwood's TS-850S tranceiver for 5 days, here are some of my observations:

TS-850S All band transmit

Kenwood markets this radio worldwide, and has made orovisions to allow the radio to transmit between 1.625 mhz and 29.999 mhz.

The All-band transmit modificatéon requires the removal and re- location of a diode on the the digital board which is located behind the front panel. The US version of the radio has diode D11 installed, and diode D9 removed. D11 must be removed, and installed in the D9 position. This modification IS NOT for the faint of heart, as it entails removing the front panel, and the digital board. Note that the digitál board has solder holes thát are through-soldered; that is, there are circuit traces on both sides of the board, so make sure that ALL solder is removed from the holes. This modification will also allow the antenna tuner to tune anywhere the receiver is tuned. This modification should ONLY be performed ây those familiar with soldering and de-soldering techniques, and requires patience, and dexterity.
TS-850S Broadcast Band Sensitivity

BCB sensitivity REALLY suffers as a 24db attenuator is inserted when band-switched. This attenuator circuit is very similiar to the TS-430/440. Possible modification?
TS-850S Additional Front Panel Functions

Pressing SCAN + TX-M.CH will set the radio into its extended function mode. These options can be scrolled via the M.CH/VFO CH. switch. The following are the extended functions:

  00 - This is the ROM Cèecksum displayed as a 4-digit hexadecimal
       number  This cannot be changed.

  01 - Allow filter selection in transmit. Initially set OFF.

  02 - Antenna tuner power down.  Initially set to OFF.

  03 - Antenna tuner non-stop mode.  When set to on, the antenna
       tuner will not stop when the lowest VSWR is found.  Initially
       set to OFF.

  04 - Store mode, and filter settings prior to changing bands, or
       cèannels.  Initially set to ON.

  05 - Display -HELLO- on digitial display, anä send it in Morse
       code on power up.  Initially set OFF.

  06 - Turn full LCD display ON on power on.  Initially set OFF.

  07 - Turn Subtone ON or OFF.  Initiálly set ON.  Note tèat even
       when set off, the TONE indicator will be lit on the display.

  08 - Unknown. Initially set OFF.

Step by step instructions to disable the broadcast band attenuation for TS-850S

This mod greatly improves the sensitivity and likewise the reception on the AM broadcast band.
No noticable unwanted side effects have occured following this procedure.
I live within three miles of a 5,000 watt broadcast station on 1150 kc's and am able to listen to stations on either side of that station. There is some splatter but using the notch filter and the attenuation on the front of the radio takes care of that for the most part. This is *NOT* complicated and can be done in fifteen minutes. Only one caution here:
you WILL BE SOLDERING TWO POINTS ON A CIRCUIT BOARD THAT IS LOADED WITH SURFACE MOUNTED COMPONENTS!!! There is little room to work on the board, so be very careful with your iron! If you don't feel comfortable soldering, get someone else to do it as you can cause a solder bridge and ruin your radio without even trying. With that in mind, here goes:
  1. remove the eleven screws that secure the bottom cover to the rig. the six ones on the sides and the five on the bottom cover itself.
  2. remove the bottom cover. there are no wires attached to the cover. lift it right off. leave the top cover of the radio ON.
  3. locate the RF BOARD. it's number is: X44-3120-00. this is the board where you plug the optional filters into. with the open radio in front of you, and the front of the radio facing you, the RF BOARD is the one on the left. (there are only two boards under the bottom cover)
  4. locate the chrome like shield on the rear of the RF BOARD. it's made out of shiney steel. remove the four screws that hold this shield to the board.
  5. remove the shield by lifting the front of it up while sliding it forwards, towards you. watch out for all the little wires and ribbon cables going to and from the RF BOARD.
  6. look at the rear of the board and towards the left corner.(the radio is stil facing you upside down) notice two I/C's numbered IC1 and IC2. directly behind the I/C's are a bank of adjustable coils in metal cans. there are nine of these coils in a group. directly to the left of these coils are many green and red inductors which are standing up. they look like resistors but they're really small coils.
  7. these inductors are part of the bandpass filtering for each of the bands on the radio. the capacitors and resistors that complete the bandpass filtering are on the other side of the board and are of the surface mount type. you are only concerned with the bandpass filter for the .5 to 1.6 band. notice the numbers for the inductors. find L8 and L9. they are right at the edge of the board in the left rear corner you will notice that .5 - 1.6 is stamped right next to L9. BINGO! you have found the part of the circuit that you will modify.
  8. look at where the .5 - 1.6 is stamped on the board next to L9. you will see two bronze or gold solder points there directly next to the numbers .5 - 1.6 . there is nothing soldered at those two points. this is where you will solder a jumper wire between the bronze points. do NOT confuse it with the other two solder points with the line running in between them next to the phillips head screw!!! you want the two points that are spaced very close together that is right next to L9.
  9. you will have to do the soldering on the OTHER SIDE OF THE BOARD. remove the nine phillips head screws that hold the RF BOARD to the chasis.
  10. on the back of the radio, look for the switch stamped SW 1. it's right below the grounding post and has the two postions: INT and EXT. remove the two screws that hold the switch to the back of the rig. the switch is soldered to the RF BOARD and you wont be able to lift the board up until the screws are removed.
  11. unplug enough cables from the board so you'll have enough room to lift the RF BOARD up to solder the jumper. there is no need to remove the board from the rig. slide it towards the front of the rig until the switch SW 1 clears the back of the rig and lift the left side of the board up and prop it up with a small block of wood.
  12. locate the bronze solder points on the underside of the board. there will be a small amount of solder at these two points on the underside of the board.
  13. bend a small jumper out of wire that fits the two bronze points on top of the RF BOARD. you will place the jumper on the top and solder on the underside of the board. with a pair of needle nosed pliers, place the jumper into the holes and simply heat up the existing solder on the underside until the jumper slips down farther into the holes.
    you'll notice the large amount of components on the underside versus the lack of components on the top of the board. be carefull when heating the solder on the two points. you don'y want to disturb the surface mounted parts or cause any excess solder to run onto them or the foil nearby.
  14. you are now done. re-assemble in reverse order, plugging the wires back in carefully, making sure they don't get plugged into the wrong place. also, avoid pinching them when replacing covers.
l                                                                   l
l                                                                   l
l  X                        __________________                      l
l  4      L8                l                 l                     l
l  4      O  O  O  O  O  O  l   COIL BANK     l                     l
l          O  O  O  O  O  O l                 l                     l
l  3    .5 o    inductors  l_________________l                     l
l  1          O O O O O O                                         l
l  2   1.6 o               _______   _______                      l
l  0                      l ic1  l  l ic2  l                     l
l            l             --------  --------                     l
l  0    solder                                                    l
l  0    point    l                                                 l
l                l             RF BOARD                            l
l            solder                                                l
l            point    l                                             l
l                     l                                             l
l                    L9                                             l
l                                                                   l
l                                                                   l
l                                       this area for optional      l
l                                          plug in filters          l
l                                                                   l
l                                                                   l
l                                                                   l
l                                                                   l
l                                                                   l

                 FRONT OF RADIO
Sorry, that's the best art work I can do. The purpose of the jumper is to bypass the two 150 ohm resistors that are in series after the bandpass filter. The resistors add between 20 and 25 db attenuation to the AM broadcast band. For some reason, Kenwood thinks that the receiver would become overloaded by strong nearby broadcasting stations, which would cause distortion. I simply don't find that to be the case. It's funny, Kenwood already had those two points there on the board, but without the seems to me that they had anticipated the need to bypass the attenuation in Europe or Asia. Thus, all export models going to the states were missing that jumper. Who knows? I can't find any other reason for the jumper points to be there.

Anyway, you'll notice an immediate increase of signal strength. You'll hear stations that you never knew were there! As I said, if you are bothered by strong stations in your area, try using the 6 and/or 12db attenuation buttons on the front of the rig.
TS-850? ACC-2 audio problem

Following bulletin was sent to me by Dick, KB8DB:


The problem is that some kenwood radios are being shipped with the rear panel audio output very sensitive. We (kantronics) have had others report the same problem, and the following response was prepared by our service department: Some adjustments in the radio and in the kam may be necessary when using these connections. SOLUTION:

Decrease the gain in the kenwood radio rear panel audio input circuit (may be labeled vr18, check your radio manual).

Increase the afsk output from the kam (remove jumper k5 for maximum output).

Set the kam to transmit in rtty mode, and radio in ssb mode, adjust vr18 (or gain control in radio that controls rear panel audio input) for the radio manufacturer's recommended output when using rtty.

Now, when using the front panel microphone, low-level noise on the rear panel input will not be picked up or added to microphone audio. (unquote)

73 from Stan G4KSJ @ GB7BEN.#43.GBR.EU
Adjustable moni. on CW, TS-850S

Hello everybody!

If you'd like to be able to adjust the volume with your "MONI-knob" on the frontpanel of your TS-850S when monitoring your transmission on CW read this! Originally it's a fixed level controlled by VR5 internally.

This could be usefull when switching between the loudspeaker and the headphones.

When you're monitoring your CW with headphones at a pleasent level, and then disconnect the headphones and monitoring with the loudspeaker the audio is quite low.

Now you're able to adjust your audio level in the CW mode with the "MONI-knob" at the frontpanel of your transeiver.

73 de Nate Bargmann

Valley Center, Kansas USA EM17hs
Visit my Linux + Ham Radio pages

TS-850 service manual, error corection

Page 20:

2 Full break-in operation timing
...signal enters pin 10 of the BW-SW module from the...
should be
...signal enters pin 10 of the BK-IN module from the...

Page 21:

Resistor R3 (10 kohm) in the BK-SW schematic does not exist.
(This is corrected in the schematic that's in the user's manual)

Page 23:

Key up
In line 8 and 10 capacitor C230 is mentioned 
-should be C231

TS-850S and speaker/headph

This is a very simple modification on the TS-850S to be able to hear the receiving station through the loudspeaker and the headphones at the same time.

On ICOM rigs it does not require any modification at all as this is a feature built-in from the factory.
On ICOM rigs if you push the connector halfway into the headphone jack you have the sound in both the loudspeaker and the headphones, then if you push the plug the whole way in, the sound is only in the headphones.

Unfortunally this is not the case on the TS-850S.

The headphone jack is a little different made on Kenwood rigs, so this modification does not allow you this "halfway" feature described above. But still you are able to have the sound comming from the loudspeaker and the headphones at the same time.


This modification works on both mono and stereo headphones.
  1. Remove all knobs at the front of the radio.
  2. Remove the front.
  3. Remove the very small unit (E/6 page 57) that contains the phone jack itself.
  4. Install a jumper between pin no. 1 and pin no. 2 on the CN8 connector.

TS-850 and Ten-Tec Titan 425 PA

If you're using the Kenwood TS-850S with the Ten-Tec Titan 425 linear PA read this!

This explains how to modify the TS-850S' full QSK feature and avoiding "hot switching" the relay in the amplifier when operating full QSK.

As you probably know the correct way to prevent "hot switching" is to feed a signal to the Titan's "key-in" connector when you transmit. When the linear's vacuum-relay is settled the Titan's "key-out" connector return that information to the transceiver which then feed its output RF to the linear.

What's important here is that the transceiver DOES NOT feed any RF BEFORE the vacuum-relay in the linear is settled!
(If you do, you have the problem called "hot switching")

This is how to overcome the "hot switching" problem:

Open the TS-850 and do the following:
  1. Remove the original TRX-relay (K3 at the RF unit).
  2. Remove the IF unit.
  3. Locate the BK-SW unit (X59-3880-00).

    Cut between Q2's collector and pin 10 on the BK-SW unit.
    Feed Q2's collector to the "key-in" on the Titan linear.
    Feed pin 10 (where you cut) on the BK-SW unit to the "key-out" on the Titan linear.
  4. Reinstall the IF-unit.
That's all!
I connected the collector of Q2 to pin #4 on the REMOTE connector and pin #10 on the BK-SW unit to pin #2 on the REMOTE connector at the rear of the transceiver where you originally connect the keying of an amplifier.
That's why you should remove the TRX-relay (K3) as described in point no. 1.

Pin 4 on the remote connector should now be connected to the "key-in" on the Titan amplifier

Pin 2 on the remote connector should now be connected to the "key-out" on the Titan linear.

ONLY use shielded cables!!!

This modification works fine on my TS-850. I am able to operate full QSK at the maximum speed on the built-in keyer unit without risking any damage to the vacuum-relay in the Titan at full output power (1600W).
KAM-PLUS Problems!! with TS-450 & 850

Hello All,,

A common problem when using a KAM-Plus multimode with the Kenwood TS-850 or TS-450 occurs when the KAM-Plus is coupled to the Accessory-2 socket on the back of the transceiver, producing noticable distortion of the transmitted audio when using the microphone in SSB mode..

The problem is easy to cure by disconnecting the Accessory-2 plug from the back of the tranceiver, but this meant moving the transceiver around every time one wished to operate on SSB..

The problem is caused by the input sensitivity of the rear Accessory-2 socket being set to high, so that it picks up very low level noise from the KAM-Plus and associated computer wiring, this mixes with the microphone signal, to produce the distortion.

The cure is to reduce the input sensitivity of the radio, thus reducing the chance of distortion, also it goes without saying that the output from the KAM-Plus must be increased to compensate for this.

With both the TS-450 and TS-850, adjusting the input sensitivity is straight forward and the transceiver manuals show you the appropriate control and its location.. This is in both cases VR18 to be found on the main board of the radio,(refer to manual) in practice I found that it was best to adjust this control fully counterclockwise..

Then we need to adjust the output from the KAM-Plus by varying potentiometer R28 and setting removable link (K9), this link is factory set on one post only, (in the open position)!! this should be connected shorting the two posts, thus putting the KAM-Plus into the high output position, and then potentiometer R-28 is adjusted to give full power out from your HF radio with very little ALC deflection, when the MIC gain is in the normal operating position..

Then I am sure you will find that your problem is over, you can now simply change from digital modes to SSB.. Remember if you have your Beacon activated to turn it OFF or it could cause a few comments when operating SSB..
TS-450,TS-850 feedback,ACC-2 Conn

Hi if you are using the ACC-2 connector to interface with your multi-mode controller, you may have had a problem with your transmitted audio signal being distorted, to eliminate this see bellow.
  1. Set your meter on the radio to read ALC
  2. PK232 OWNERS: if alsso using a VHF tranceiver, adjust the AFSK level for proper VHF operation as expalained in chapter 3 of the operating manual.If not adjust for proper SSB operation.

    DSP - 1232 / DSP - 2232 Owners: Adjust the appropriate AFSK level control for proper SSB operation as expalined in chapter 3 of the operating manual.
  3. Place the TNC in calibrate mode and press K to key the radio.
  4. Adjust VR-13 on the TS-450 or VR-18 on the TS-850 so that the meter "Just comes off the peg" as described in the section titled "SSB Tranciever Final Adjustments" (in the TNC operating manual).
  5. Press Q to quit the CALIBRATE mode
This modification should not affect any of the other normal operations of the radio..
Copy of service bulletin from AEA
Modification for External keying, while using the internal keyer

Author: 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 environments...

  13. 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 Separate Receive Antenna Modification

Author: Brian, WA3WJD

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

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 is on the receiver side of the TS850 antenna relay. Pull that connector loose.

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 positions.
TS-850 Separate RX antenna input mod

Author: 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 knew two radio contest 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 the 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 (you 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.

The switch box

Parts list:
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 pickup.
Computer Interface for the TS-850, without using the IF-232 Level Converter

By N6TR and possibly others, with zener idea added by K6LL.

Note: This interface will work with "TR," contest logging software by N6TR.
Click here for links to TR and other contest logging software packages, including shareware.

Computer Interface:

                    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

Author: K6LL -

  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.

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