1. Remove top and bottom covers.
2. Remove the top screw from each side of the front panel assembly.
3. Carefully rotate the front panel forward to gain access to the control board(x53-3560-11 a/4). This board is mounted vertically against the body of the transceiver. It is not the board that is mounted in the front panel assembly.
4. Locate and remove resistor R244 from the control board. R244 is below IC12 ROM and above IC23. There are two chip resistors, one on top of the other -carefully remove or break the top one..it is easily fractured -that's R244.
5. 5. Reassemble and then perform the cpu reset by holding the A=B button depressed as power is turned on.

1. Remove the bottom cover of the TS-870S
   
   
2. Remove the shield that covers the TX-RX board which is located on the right side of the bottom of the transceiver.
   
   
3. Carefully remove IC4, IC5, & IC6 from their sockets and replace them with the new parts listed above.
   
   
4. reset the transceiver by holding the [A#B] key depressed as power is turned on.

1. Make sure the pins of the new EPROMs are properly aligned before insertion. New EPROMs tend to have the pins spread aout wider than the socket. The pins can be beat in by pressing each side of the EPROM against a static free work surface.
   
   
2. Avoid touching the EPROM pins. Graps the device from the top and bottom epoxy body ands between thumb and forefinger.
   
   
3. Avoid inserting the EPROMa backwards.

RF PCB:
R157         1,8K  to  560      RK73FB2A561J
R160,161     2,2K  to  1K       RK73FB2A102J
R164         1.5K  to  560      RK73FB2A561J
R169         1K    to  330      RK73FB2A331J
L76,79       3.3u  to  0        R92-0670-05

TX-RX PCB:
R332         2.2K  to  6.8K     RK73FB2A682J
C340         .022u to  .01u     CK73GB1C104K
VR1          470   to  3.3K     R12-6737-05 (optimal)

1. Remove the bottom cover and shields anclosing the RF board and TX-TX board.
   
   
2. Replace L76 and L79 on the component side of the RF board.
   
   
3. Replace C340 and R332 on the component side of the TX-RX board.
   
   
4. Access the bottom side of the RF board and replace R157, 160, 161, 164 and 169.
   
   
5. Perform S-Meter alignment step 8, on page 95 of the Service Manual. If you cannot obtain "05" of the display, replace VR1 on the TX-RX boardwith the part listed above.

I loved the TS-870 when I first got it. Size is ideal for expedition radio, light weight, fits in carry on luggage. Features and computer controls are excellent, until I used it in the contest on 160m. Bloody thing got overloaded with signals 4 kHz away. Everybody was QRMing me! What a piece of blinking junk! Liking the radio otherwise I inquired at Kenwood about the problem of overload. They came up with modification to remedy the gain distribution in the RF and mixer stages, which was implemented in later production models. After I received the service manual, I started to dig into the radio and came up with few more improvements.

Earlier production units before S/N 801xxxxx had problem with front end overload and consequent distortion and crossmodulation in the later stages, including DSP, especially noticeable on low bands. To remedy that on those earlier units see the Overload Modification.

There is an absence of 2nd RX antenna switching (Beverages, etc.). When I inquired at Kenwood, they supplied modification instructions that required some drastic modifications, including cutting the traces. When I obtained service manual, I figured very elegant modification using just plug in diode. See 2nd RX Antenna Switching modification.

Examining the circuits and filtering arrangement, I have found that Kenwood engineers decided to rely on obtaining the selectivity mainly by using the DSP. Theoretically it is great, except when strong signals blow by the mediocre crystal filters used in stock TS-870, they modulate the following stages, including DSP circuits. The biggest improvement that puts this radio one class higher, is to replace the stock 2nd IF crystal filter and 3rd IF monolithic ceramic filter with high quality International Radio or other filters. Any better shaped filters make tremendous improvement to the selectivity, overload and DSP performance. Depending on intended use, you can use 2.7, 2.4 or 2.1 kHz bandwidth filters. I chose 2.1 mainly for contesting purposes. It is possible to use narrower filters for CW operation, but selectivity selection scheme via microprocessor controlled switching makes it complicated and throws the controls off their markings. I found that 2.1 filters work very well even for CW and are significant improvement over stock arrangement. See Filter Modification.

Overload Modification

NOTE: the changes do not apply to radios with S/N 801xxxxx and later.

Adjustment:

2nd RX Receive Antenna switching modification

Kenwood TS870 has two antenna jacks ANT1 and ANT2 and external receiver antenna jack (RCA type) that can accommodate external receiver when activated through the program menu. This adds some attenuation to TS870 receiver signals. There is no provision for external receive antenna switching (Beverages, preamp., etc.) When I inquired Kenwood about this option, they sent me modification instructions that required cutting the traces and rewiring the ext. RX connector. When I received my Service manual and had a look at the circuit, I came up with this simple modification:

Parts needed: 1 diode (any type) I used rectifier diode, generic NTE125

1. (In the following references the front panel of the rig is facing you.)
   Remove the top cover.
   
   
2. Remove 7 screws holding the cover over the FILTER and RELAY unit (in the middle) and remove the cover. (Where the ANT1 and ANT2 connectors go.) This exposes two PC boards.
   
   
3. Locate the connector CN301 on the RELAY unit (adjacent to ANT1 and ANT2).
   It is about 1 inch back and 1 inch left from the ANT1 connector and has three wires going to it - two gray, left and one black, right.
   
   
4. Take the diode, clip the leads to about 0.5 inch length, bend them down and form them so they are spaced about 1/8" and parallel (kinda forming letter Y).
   
   
5. Plug the diode into CN301 connector from the top, pushing the diode wires between the plastic housing and the metal contacts of the connector. Cathode (the end with the band marking) of the diode should go to the middle contact (gray wire), the other end to the left contact (gray wire). Make sure that diode makes good contact with terminals of the connector. Black wire should be free.
   
   
6. That completes the modification. Replace the covers, do not pinch the wires going to the antenna tuner!

Operation:

Connect your transmit or main antenna to the ANT2 connector. Connect your receive antenna or preamp output to ANT1 connector. Now you can transmit only through ANT2 connector.
Front panel button ANT now allows you to select ANT2 (receive/transmit on ANT2) or ANT1 (receive on ANT1, transmit on ANT2). Antenna tuner would always see the impedance on ANT2. The way the switching works, whenever you transmit, you will switch ANT2 on transmit, regardless of ANT1 or ANT2 selection. Much better use of connectors than originally devised by Kenwood

Notes on TS870 usage: Normally there is enough gain on the receiver for beverages. In case that you need to use the preamp or preselector, than turn the AIP on TS870 on, and if needed add the attenuators. Try to keep the noise level peaks close to low end of the Smeter scale. Helps with intermods. If using DSP, play with different settings and different levels of AGC setting, it has effect on overall behavior.

Filter Modification.

Major improvement in selectivity and DSP performance can be achieved by replacement of 2nd and 3rd IF filters with sharp crystal filters, like from International Radio. The 2nd IF 8.83 kHz filter used in TS870 is the stock Kenwood crystal filter, while the 3rd IF 455 kHz filter is little ceramic Murata filter.

I have ordered set of 2.1 kHz filters (8.83 and 455) from IR. The modification involves removal of printed circuit boards where the filters are located, unsoldering the old filters. In their place solder short piece of miniature coax to connect new IR filters. IR filters can be mounted between the circuit boards and the metal chassis using double sided sticky tape. Coax from old filter connections is then connected to new filters. Tweaking the matching IF transformers next to the filters ensures proper match and gain.

Other filters with wider bandwidth can be used also. For contesting I found 2.1 filters to be the best and the mod works very well on CW also. Selectivity improves as well as functions of DSP. Now it is a decent radio, matching those costing thousand(s) more.

Good luck and I am not responsible for any goofups you make! :-)

When I got the TS870S first I was really not amazed about the selectivity, also not about the quality of the build-in front end. But the filter-mod and also Kenwoods front-end-mod helped to solve these problems. But there was one additional possibility to improve something. When I reduced the output power to drive a bigger linear, I found, that the ratio is changing between SSB in comparison to modulate with a single-tone. If the percentage was 50% between voice and CW using 100W output before, the ratio is dropping down if you are running only 10W (measured with a peak-meter).
That is not very helpful, because its not easy to drive the linear correctly in that case. And you cant improve that using higher microphone gain or processor. The reason is Kenwwods ALC-curcuit (its like the TS50S) which can be found on the RF-unit. In the curcuit diagram its named "Reserve Current Prevention". This part is directly controlling the TX-amplifier Q39. And this part has normally nothing to do with the power adjustment or regulation. But using lower output its more sensitive and therefor more effective.

Turn your TS870 on its head (foots up) and remove the cover. If the display is looking into your direction, the big curcuit board on the left-hand-side (underneath an additional metallic shielding) is the RF-board. Remove all connections carefully and afterwards the complete board. There are 3 electrolyte capacitors named: C286, C287, C289. Place a small resistor (I used a small chip-resistor) with 1 KOhm in parallel to C289, which is in the middle. Best is to do that on the soldering side (not component side).
Thats it ! Bring the TS870 back to live and afterwards you will see the improvment in SSB-mode and you can easily measure it. Everyone told me afterwards, pumping effects are gone and my voice sounds fresh and clear (is that possible with an age of 40 ?)
If you are only running your rig with full output, its not neccesary to realize this mod. In my case I am going down to 5 Watts - afterwards I´m driving an attenuator going down to 20 mW (-24dB) and this is driving a commercial russian linear with the possibilty of 2KW out (+50dB). Therefor its absolutly necessary to have stable conditions.