ts 930 cos.pdf

W6NL Mods for the TS-930

Introduction

The Kenwood TS-930, while many years out of production and lacking many of the technology

developments of the past twenty years, continues to be an excellent HF radio with a unique ability

to hear multiple signals in a pileup. This particular performance advantage has, for whatever

reason, eluded the designers of more modern radios. As a partner in the new HC8 contest station

on Isla San Cristobal, I undertook to obtain and refurbish a number of 930s, but we were

disappointed by the lack of reliability we experienced.

The problems we observed included

1) Several radios experienced outright power supply failure, and one had a difficult-to-trace low

frequency oscillation in the 28V circuit that involved the output amplifier, and destroyed amplifier

driver bias transistors (this was cured by replacing the 2N5885 regulator transistors).

2) One radio experienced intermittent loss of receiver sensitivity, and another experienced loss of

microphone input on SSB.

3) AGC overshoot made reception difficult of signals in the range of S9+20 dB.

I aligned each radio and ran it for a four-day period at high transmitting duty cycle on CW and

SSB, using computer logging software to transmit into a dummy load (which itself required a

cooling fan). At the end of the burn-in period I checked for unchanged sensitivity, power output

and fan operation. Despite this we experienced failures in contests, with the requirement to return

the radios to the US for repair.

I was aware of the change of TS-930 design at S/N 310XXXX that responded to the many early

problems (digital board through holes, amplifier through holes, receiver muting, sidetone, etc.)

that are well documented in listings of modifications, as well as in Kenwood's application notes.

Our radios have serial numbers ranging from 4M to 8M. All have been standardized to the same

configuration, so we would be able to separate the sources of any problems. All our radios have

the stock CW and SSB IF filters (TS-930 SSB filters are wider than the pin-compatible ones for

TS-940/850) and the PIEXX digital board, both for reliability, new functions such as main tuning

knob control of RIT when dial is locked, and to be able to use computer logging and control.

It should be noted that the power situation at the end of a long rural line is not favorable, nor is the

fact that our radios experience the rough handling as airline baggage (even in the excellent foam-

lined Pelican cases) and then sit idle for extended periods in the foggy and humid equatorial

mountain-top air. In order to minimize our exposure to line voltage variations and surges, we

configured all the radios for 240V operation and used professional-grade surge protection. The

short line cords are a unique color and are firmly attached to the radios so other equipment in the

shack cannot inadvertently be connected to 240V through the standard EIA connector. We have

the option to switch to 220V if the line voltage sags, although that has not been necessary.

With the modifications outlined in this note, our TS-930s now exhibit excellent reliability, and

have worked well for the entire preparation and contest time in both modes of the recent CQWW

contest. I thought there might be some interest in what I found was required to make them

bulletproof.

- 1 -

Replacing TS-930 Resistors and Shunt Zeners with Series Regulators

The TS-930 power supply for serial numbers higher than 310xxxx generates two voltages, 28.5V

for the power amplifier and antenna tuner, and 21.7V for the digital board and the signal board.

The 28.5V is regulated by the two TO3 pass transistors on the heat sink, and the 21.7V is

generated by separate transformer secondary taps and diodes that generate 31.9V which is reduced

to 21.7V by the TO220 transistor on the power supply heat sink.

Diode

Quad

XFMR

40V

Org

+28.5V

31.9V

Yel

+21.7V

The power switch has a pole that opens the +28.5V to most of the radio, including the circuit that

runs the 21.7V regulator. This is apparently so the radio will just turn off without the time delay

and rude noises of the filter capacitors discharging.

The power supply uses high-wattage resistors and zener diodes in the power supply fan case to

reduce the 21.7V secondary supply voltage 7.5V and 15V for the digital board (which has 5V and

12V regulators) and for the signal unit, which has an 18V regulator. The 21.7V is distributed by

the yellow wires via a black terminal block between the antenna tuner and the filter unit; this block

also has the switched +28.5V orange wires. The original circuit looks like this:

82 W

Gray

82 W

21.7V

22 W

15V

Yel

White

7818

18V

470 uF

On signal

unit

resistor that is the third

supply voltage for the digital board connected to the 21.7V instead of the 28.5V line.

The dissipation in the resistors and diodes is above their ratings, and this could be a reliability

- 2 -

The main schematic diagram of the radio is wrong, it shows the 33

problem. This new circuit replaces the resistors and diodes with 78xx 1 A. TO220 regulators

mounted on the power supply heat sink. In addition to having less dissipation, the regulators are

short-circuit proof. There are holes in the heat sink, and the TO220 tabs can be bolted with 4-40

small-pattern nuts and bolts. I use a locking compound on the bolts so they won't vibrate loose

later.

7808

Gray

0.33 uF

50V

1 uF

50V

21.7V

15V

Yel

7815

White

1 uF

50V

7818

18V

470 uF

On signal

unit

The regulators need capacitors near them, especially if they are driving the PIEXX board, which

has switching regulators with inductors at the input. The regulators should be prewired, and the

wires are connected to the voltage points inside the power supply fan case.

To make the change, proceed as follows (the same steps are necessary to replace the pass transistor

with an NTE377, if the original is burned out).

1. Unplug the radio and remove the top cover .

2. Remove the four black screws holding the fan case onto the heat sink, and unplug the fan wire

from the power supply board so it won't break at the fan connection. Free the tab from the case

bottom, and tip the case down and put something under it to hold it horizontally to work on.

3. Remove the remaining two black screws holding the power supply heat sink to the radio. You

will find the heat sink will not tip out without additional work.

4. Unscrew the screw holding the diode bridge to the heat sink. This screw will be retained by the

heavy wires from the transformer, so you don't need to pry it out completely, just free the diode

quad from the heat sink so the heat sink can move.

5. Remove the two lugs and heavy red wire from the TO3 pass transistors by unscrewing the two

middle screws while holding the nuts with long-nose pliers on the inside. Leave the screws in

place in the transistors to hold the insulating washers.

6. Now you can tip the heat sink forward far enough to be able to reach the screw that holds the

pass transistor. This transistor has had loose screws in some radios, so tighten it up while you

can. If you unplug the pass transistor, be sure to note which way the plug goes on (some have

plugs, some have the blue, green and violet leads soldered on and covered with heat shrink tube).

- 3 -

7. Locate the field of small holes near the upper edge of the heat sink, near the outside edge of the

radio. As viewed from inside the radio, the two regulators mount to the holes in the bottom row

(the top row is also OK, and easier to reach if you are not removing the heat sink). Before you do

anything else, route the wires from the regulators beneath the heat sink so they can be connected to

the terminal strips in the fan case.

7815

7808

1 uF

0.33 uF

1 uF

Gray

Blk

8. The 4-40 small pattern nut just fits between the heat sink fins. Use a thin tool that can hold the

nut on the end, and orient the flats of the nut to go between the fins. It's helpful if the parts are

magnetic, so you can recover a dropped nut (be sure to cover the holes in the chassis with tissue or

a rag). Use a 4-40x3/8" screw to fasten the regulators to the heat sink. The same nuts and screws

are used in DB9 and DB25 connector shells. I use some heat sink compound on the back of the

regulators. No insulation is required. Check again to be sure the screw for the TO220 pass

transistor is tight and the transistor is oriented up so you can get to the terminals.

9. Reconnect the lugs to the backs of the TO3 pass transistors, holding the nuts with log-nose

pliers and using a drop of retaining glue or Loctite. Reattach the diode quad to the heat sink.

10. Attach the heat sink to the radio with the middle black screws. Check that there are no wires

being pinched between the heat sink and the chassis. Now you can hook up the regulator wires to

the terminal strips in the fan case.

11. The resistors to be replaced are inside the power supply fan case. You will notice that the

resistors will have lost their color coding from overheating, and the terminal strips may be

somewhat charred, from overheating. Cut out the two 82

resistors and their zener diode, and cut

resistor and its two zener diodes. You can save these in case of trouble, but the new

circuit should be more reliable.

- 4 -

Yel

out the 22

Blk

Org

FAN

Be sure White

wire is not broken

23V

Yel

7.5V

Gray

Brn

Red

Yel

21.7V

Org

28.5V

7.5V 15V

Digital Board

Dial

Lights

The fan case should now look like this:

Blk

Org

Yel

Blk

FAN

Be sure White

wire is not broken

23V

Yel

7.5V

Gray

Brn

Gray

Yel

Blk

Red

Yel

21.7V

Org

28.5V

7.5V 15V

Digital Board

Dial

Lights

- 5 -

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