lørdag den 26. maj 2018

Kenwood TS-440 error: dots-in-display

Kenwood TS-440 can develop an error where only dots are shown in the frequncy part of the display. When the microprocessor in TS-440 detects a PLL unlock condition, it blanks the display and shows a row of dots. See the picture below.

Kenwood TS-440 with dots in the display caused by PLL unlock.

There are 5 PLL's in the TS-440 and any of them can cause the "dots".

There are 2 PLL's where glue was added at the factory to protect the circuit against vibration. Over time the glue can become conductive because it absorbs moisture from the air. Conductive glue is poison to a VCO, which is highly sensitive to voltage changes.

VCO5 (PLL-unit) is used on all bands. It will affect all frequencies if VCO5 goes into the unlocked state.

VCO1 (RF-unit) consists of 4 separate oscillators. Together they cover the entire operating range of the radio. If one of the oscillators is unlocked, it will affect the range covered by that device.

What is the solution to the dots-in-display problem?

My solution is radical and labor intensive: I remove all components from VCO1 and VCO5 and clean the PCB thoroughly to remove all glue. Then I fit brand new components and adjust the VCO. The PCB is then reinstalled into the transceiver and a final alignment of the VCO's is performed.

The method above has shown good results, and I have done it twice. You can read more by visiting http://oz1bxm.dk/TS440/ts440-repair.htm

Vy 73, OZ1BXM Lars Petersen
Web-page: oz1bxm.dk

2 kommentarer:

  1. I have read with interest your, and many other, articles on the Kenwood 440 display problem, but I have been unable to see a problem similar to mine and wonder if you have an opinion.My TS440S,at power on, displays a frequency for about 500msec,.,then goes to steady dots.If any of the function buttons are pressed, a frequency is displayed,1/2 sec,then return to dots.The same thing happens when rit/xit turned,mode keys pressed, up/down and band buttons pressed. The display will also come up and change if the tuning knob is turned and remain on as long as it is moving.The potting material has been removed from both VCO's and the memory cell reads 3.4 volts. 73 .Richard.

  2. Hello Richard,

    I have seen the same behavior: A short moment of "display works all right" but then the "dots in display" error comes. This is probably due to an oscillator error (VCO1). The oscillator frequency is within range for a short time, then it gets out of range. The PLL stops working and "dots in display" is shown.

    My suggestion is to measure the loop voltage at TP10 (PLL unit). Is it within range? If not, the oscillator has a problem, and you have to troubleshoot it. This can be tricky! I hope my page on this problem can be of some help for you:

    73, OZ1BXM Lars