Kenwood TS-850s Noise Blanker Mod - G7SYW's amateur radio bits & bobs...
 

Kenwood TS-850s Noise Blanker Mod

| Posted in Technical Topics

Most owners of this radio would agree that the Kenwood TS-850 is a very good radio except for the noise blanker.

The most common modification for the noise blanker circuit is well documented.
This modification requires the removal of two SMD capacitors. While this is a very quick and easy task to perform, finding the correct components to remove can be awkward if you’re not sure where to look.

The second method involves adding a couple of components to the board upon which the front panel controls are mounted.

I have performed both methods and these are shown below with photographs to make component identification easier.

As with all modifications I accept no responsibility for any damage to you or your equipment through following, or attempting to follow, the information given here. This information is for reference purposes only.
If you don’t feel confident working inside your radio – find someone with enough experience to carry out any work for you.

In both methods, I shall assume that the radio’s covers have been removed.

Capacitor removal method

With the radio up the correct way, and the left-hand side facing towards you, locate the noise blanker board. It is located roughly beneath the speaker and is approx 5cm x 8cm in size.
Kenwood TS-850 NB board location

This unit is held in place by four screws. It’s possible to remove the board far enough to gain access to the capacitors on the bottom of the board without disconnecting any cables.

With the board removed located the two capacitors that require removal. These are C618 and C619 – found on the schematic in the service manual.
Kenwood TS-850 NB-Board

The capacitors may be removed by heating them up with a soldering iron, then gently using the tip to remove them from the board.
A small amount of adhesive is used in production to hold them in place during manufacture. The heat from the soldering iron is enough to soften the glue allowing easy removal.

Ensure that there are no solder bridges once removed. The glue may leave some residue which looks unsightly but is harmless.

Reinstall the noise blanker board and any connections you have removed. Finally replace the radio covers, being careful not to trap any wires when reassembling.

Component addition method

Just two components are required for this method, a 2.2K ohm resistor and a 3.3uF 10v tantalum capacitor.
Begin by facing the radio towards you, and up the correct way. Remove the two top screws holing the front panel, one from either side. Loosen the bottom screws just enough to allow the front panel to drop forward. You need just enough room to remove the small board holding the Notch/squelch and noise blanker controls.

Remove the inner and outer knobs from the controls, followed by the nuts holding the controls to the front panel.
Carefully withdraw the board from behind the front panel. This modification can be done without removing the board fully.

Solder the positive lead of the capacitor to the wiper terminal of the inner noise blanker control. Solder the negative lead to the ground side of R6.

The resistor is soldered in the position shown, effectively across R5. It is easier to solder the resistor in the location shown than trying to literally bridge it across R5.
Kenwood TS-850 NB controls

A physically small electrolytic capacitor could be used if the tantalum type is not available. Keep both components as close to the board as possible as there isn’t much room between this board and the switch board once reinstalled in the radio.
Kenwood TS-850 NB controls in situ


Please leave any comments below if you have tried this mod and had success or otherwise…


Leave a Reply

Your email address will not be published. Required fields are marked *