DRM 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:
You will need: a 1K Resistor, a 1mF Capacitor, a Shielded Cable (RG-174 works great, and the Times Microwave LMR-100 is AWESOME!)
- 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.
- 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!
- Solder the free end of the resistor to this leg.
- 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).
- 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!