Kenwood TS-430S Repair and Restoration. November 2018

Overview of TS-430S transceiver and faults

The TS-430S is an iconic HF transceiver from the mid-1980s. Despite having had several owners, this particular radio is in moderately good condition, with all knobs and markings intact.

However, in recent times, the radio has developed various issues in both receive and transmit functions, rendering it completely useless. These are common problems not only with this model but also with many similar models from the same era. The radio exhibits slow startup and stabilization, along with an unstable tone in the receive audio. The receiver's sensitivity has significantly decreased across most of the band pass filter groups. Additionally, the transmitter experiences intermittent power level variations, and the VFO is unstable.

After undergoing a comprehensive restoration and repair project, all operational faults of the radio have been successfully resolved. General maintenance and a thorough cleanup were also performed, resulting in a radio that feels as if it were new and is a pleasure to operate.

List of issues requiring attention:

• The radio is slow to start up and stabilise.

• There is an unstable tone present in the audio.

• Receiver has low too very low sensitivity on most of the band pass filter groups.

• The transmitter has intermittent power output.

• The S meter is very unresponsive in most receive modes except FM.

• The VFO is often unstable.

• The S meter back light failure.

• Superficial paint damage.

Measure Receiver Sensitivity and Maintenance of the Filter Unit Board Repair

The receive issues were tackled first, and the first step involved measuring the current MDS (Minimum Discernible Signal) level on all bands to establish a benchmark for any improvements. Receiver sensitivity figures are typically expected to be better than -120 dBm, while MDS levels of -60 dBm indicate extremely poor performance, effectively rendering the receiver deaf.

The TS-430S Filter Unit board switches various bandpass filters using relays, and the MDS results obtained below clearly indicate that the tested frequency groups correspond to the various bandpass filter ranges. This provides strong evidence that oxidized relay contacts are the likely major cause of the poor receiver performance.

Table 1  MDS (Minimum Disenable Signal) measurement results.

Receiver Sensitivity Repairs

The Filter Unit (X51-1290-00) was removed from the radio for detailed inspection, and the contacts of relays RL1 to RL15 were cleaned by wiping them with a small sliver of gloss paper soaked in contact cleaner. Gloss paper was used to avoid being too abrasive on the silver-plated contacts, and the choice of gloss paper ensured that no paper fibers would be left behind to disrupt ideal electrical contact.
 
All plugs and sockets on the Control Unit (X53-1290-000), IF Unit (X48-1370-00), Control Unit (X53-1290-00), RF Unit (X44-1510-11), and FM Unit (X48-1340-01) were unplugged, cleaned with contact cleaner, and re-plugged. This process was repeated several times to ensure good electrical contact. Additionally, the RL1 relay on the RF Unit (X44-1510-11) was cleaned, similar to the Filter Unit relays.
 
The results of eliminating all the poor contacts within the radio were significant: the radio regained full receive sensitivity, and the power and signal strength meter started providing meaningful readings again. Furthermore, the transmitter regained stability.

 Fig 1 Filter Unit (X51-1290-00) board layout

 Photo 1 Filter Unit (X51-1290-00) board layout

 Fig 2 Filter Unit (X51-1290-00) relay section schematic 

Unstable tone present in the audio during start up.

The receiver experiences a strong, unstable, and highly irritating tone during start-up, which gradually diminishes over a period of 5 to 10 minutes but never completely disappears. During this time, the tone registers around S10 on the signal strength meter, and the receiver's sensitivity is significantly compromised.
 
Upon conducting the initial inspection of the radio, it was observed that the IC9 5-volt regulator chip on the IF Unit (X48-1370-00) was excessively hot to the touch. The IC9 regulator is responsible for supplying power to the frequency Display (X54-1630-00) board. By touching the area surrounding the IC9 regulator and the wiring connected to the Display board, it was found that the annoying tone would change in both amplitude and frequency.

Repair

All the electrolytic capacitors on the Display (X54-1630-00) board have been replaced, but there has been minimal improvement in the tone. However, the tone now completely disappears after the 5 to 10 minute period, whereas previously there would often be a small residual tone remaining. The replacement of the electrolytic capacitors is generally beneficial, as they can be potential failure points in older radios.

Table 2  Display (X54-1630-00) board capacitor replacement.  

Fig 3 Display (X54-1630-00) schematic 

The electrolytic capacitors C118 and C119 on the IF Unit (X48-1370-00) board have been replaced and the IC9 AN7805 5 volt regulator has also been replaced with a LM7805CT.

Table 3 IF Unit (X48-1370-00) board capacitor replacement.  

Fig 4 IF Unit (X48-1370-00) 5 and 8 volt regulator section schematic 

The replacement of the above-mentioned electrolytic capacitors has resulted in the complete disappearance of the unstable tone during start-up, and the radio now starts up perfectly without any signs of instability. Surprisingly, the instability with the VFO has also completely disappeared.

Replacement of the TS-430S meter backlight with new bright LED

Photo2 TS-430S backlit display

The incandescent meter backlight had failed and required replacement. While a simple like-for-like replacement was possible, a much superior solution was available with bright LED (Light Emitting Diodes) lamps. LEDs have many superior characteristics compared to traditional incandescent lamps, particularly in terms of reliability. However, they may not always be an ideal solution. One key performance difference is that LEDs radiate light forward in a narrow beam of between 10 and 20 degrees, unlike the more omnidirectional pattern of most incandescent globes. Therefore, if the backlight relies on a more omnidirectional light, the replacement process is not as straightforward as simply replacing the existing incandescent globes with newer LED lights.
 
Fortunately, the TS-430 radio is well suited for LED backlighting for the meter. The 5mm LED is a good physical fit, and the tight angle of the LED is well suited to the display light guide. The TS-430 radio's dial light is powered by a 13.8V DC supply. It was found that using 1.2k ohm 0.25 Watt resistors in series with the 5mm White, 45000mcd LED provided good results and a lower running current. The 1.2k ohm current limiting resistor should provide a very reliable, long life for the LED. 

The 5mm LED snugly fits into the existing rubber grommet and can be slightly adjusted for optimal effect.

Photo3 The 5mm LED fitted in the exiting rubber grommet and mounting bracket.

LED details

Size (mm) 5

Colour White

Lens Waterclear

Viewing Angle (Degrees) 15

IF Typical (mA) 30

VF Typical (V) 3.2

IV Typical (mcd) 45000

IF Max Continuous (mA) 30

The above calculation is for maximizing LED performance. However, during the fitting of this LED with the TS-430 radio, it was determined that a 1.2k ohm 0.25W resistor for this particular LED was sufficient. This resistor choice will greatly improve the life of the LED, and it was observed that the 0.25W resistor did not even get slightly warm.

Photo4  Fully Repaired and Restored Kenwood TS-430S

Video of the Kenwood TS-430S Repair and Restoration

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Page last revised 12 September, 2024