TS-870 Mods  

Frequency expansion                                                                               MARS, CAP
  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.

              

4KC filter

The TS-870 has a 3KC stock filter (YK-88S2) located on the bottom side. By swapping out this filter for the Inrad 4KC filter (#475), you'll be able to have better sensitivity on receive with
less "hiss". On the transmit, you will gain better fidelity, the lows will be slightly richer, the mids and highs will be a little smoother and the separation between them are more noticeable. Furthermore, if you are using rack gear, you can push your EQ's and compressor harder without reaching the threshold of "tearings"
as quickly. You will NOT gain any more bandwidth by swapping out the stock filter to this Inrad however. This is a fairly simple mod to do. The most difficult part is the removal of the stock filter out of the filter board.
A note on removing the filter board: You definitely want to make a simple sketch as to which jumper goes to where or simply take a digital picture of the thing before you start un-plugging.

For more information Click on Here
TS-870 ACC2 Audio Input

C131 Capacitor Modification:
Source courtesy of LA4WAA - Original mod by W9AC

It has been documented by several Kenwood TS-870 owners that feeding audio to the ACC2 rear input, instead of the front panel mic input, results in lower distortion audio. This is because some of the speech amplifier circuits are effectively bypassed that are the source of the distortion, especially in the high frequency area above 2kHz.

However, because the ACC2 audio input of the Kenwood TS-870 was designed for data audio (such as that from a TNC using the digital modes), the audio characteristics of the ACC2 audio input are attenuated below about 200Hz.

The following modification addresses this issue by changing the value of the C131 capacitor that the ACC2 audio input travels through, allowing low frequency audio to freely pass through the circuit.


C131 IN THE SCEMATICS:

C131 Schematic
Click to enlarge

C131 Modification Procedure:

  • REMOVE BOTTOM COVER

Kenwood TS-870 Bottom Cover Removed

  • REMOVE METAL SHIELD FROM PCB

Kenwood TS-870 TX/RX Unit Exposed
Click to enlarge

  • REMOVE ALL THE WIRES AND RIBBON-CABLES AND SCREWS FROM PCB
    Look for IC-23 - Capacitor C131 is under the PCB in that area.

  • LOCATE THE CAPASITOR ON THE BACKSIDE
    C131 is on the solder side of the PCB. With a beeping ohm-meter, find the connection from pin 5 on IC-23 to the R137 (1K) witch is under the PCB, to the left of C131 on the picture.

C131 Mod Finished
Click to enlarge

  • SOLDER THE NEW CAPACITOR WITH "PIGGY-BACK" METHOD
    (DO NOT remove the original C131)

    Use a mini 4.7uF/35V from ELFA (67-195-20). This fits nice under the PCB. The positive lead to the direction of IC-23 and the minus lead toward the front, like seen on the picture.

C131 Mod Finished
 TDRM TS-870DRM TS-870 MOD

 

The modification described here has been documented by others, and by all means, I am not the inventor. However, this is the procedure I followed to modify my TS-870, and also, provide an external connector that I can plug into for the 12KHz IF. As you will see, I integrated this into the ACC jack of the radio, at the rear. Some mods on the Internet tell you to desolder the IF cable, and place this in its place. This is NOT needed! You can keep the IF cable, and do this mod easier.

The modification is very simple, does not require ANY De-Soldering, and there are no holes you need to drill in your radio!

The location of the 12KHz IF is located on one leg on C144 Capacitor, which is located on the TX/RX unit of the Radio (X57-4620-00 in your service manual). The Area of Interest is as this:

schematic

You will need: a 1K Resistor, a 1mF Capacitor, a Shielded Cable (RG-174 works great, and the Times Microwave LMR-100 is AWESOME!)

  1. Connect one end of the resistor to the capacitor, and leave the other end for connecting to C144 on the radio. Connect the other end of the capacitor to the center conductor of the coax. Shrink wrap around the area, so there are no shorts, as the shield is not needed.
  2. Open the radio, and locate C144 as per the diagram above. PAY ATTENTION to the side which the tap will be connected! Is in on the c144 side which connects to the Q16 and R150!
  3. Solder the free end of the resistor to this leg.
  4. Run the cable around the radio, and then solder the center conductor to the back of the ACC connector, on PIN #1 (PIN#8 Can be used for your Ground to this). Just simply tack the center conductor to the exposed pin (as seen in the next page).
  5. You are done!

The reason for the 1mF capacitor, is that this will provide proper coupling to the radio, and will PROTECT your radio in case you short out the cable pins! PLEASE use it!


This is where the cable assembly is connected

mod1

This shows you where PIN#1 on the ACC connector is located in reference to the chassis. Notice also how I routed the LMR-100 cable in the chassis. This mod works AWESOME!




Remember it is Illegal to transmit out of band. This Modification is for Informational purposes ONLY.
Doing such modifications on your radio may void any warranty and damage your equipment.
All mods found on this database are offered to me by other amateur radio hams or captured by Packet system. 
KB2LJJ  take no responsibility or liability for any damage done resulting from any modification.  

ATTENTION
The KB2LJJ takes no responsibility for any damage during the modification or for any wrong information made on this modification.