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KENWOOD TS-940S SERVICE MANUAL PDF

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Unplug all external radio connections.

Manual kenwood ts-940s pdf service

Remove top and bottom covers. Remove 4 screws holding the faceplate to the chassis on the right and left side of the faceplate. Gently pull the face away from the chassis about an inch for working room, but don't unplug anything.

KENWOOD TSS Service Manual download, schematics, eeprom, repair info for electronics experts

With unit sitting upright, locate Digital Unit B. It is on the right front corner right behind the faceplate.

Service pdf manual ts-940s kenwood

If you have a voice synthesizer unit the voice unit is mounted to the top of it. If not, there are 4 raised mounting holes on top to hold the voice synthesizer unit. Remove the 4 screws from the VS-1 board, and fold it out of your way to the left. Remove the 5 screws 3 on left, 2 on right from the Digital Unit B shielding. There is no need to disconnect any connectors.

Tip the Digital Unit B shielding case up from the right side. Use something to hold it up for you. Now simply look on the lower right hand corner of the board.

Locate IC Now look up and to the left and you will find D Snip one lead of D That's it. To test, attach a dummy load and transmit out of band. Now Go back through the steps and put the unit back together. Now find diode and cut it for all-band transmit. Remove jumper wire JP7 and replace it with the parallel combination of the 15 Kohm resistor and the 1S diode.

Pay close attention to polarity. You should know that it can be even better if you do some corrections. In these pictures the FETs are in the wrong position. I can assume that thousands of other TSS are also waiting to be corrected and perform Rx even better mistakes "hidden" for almost 20 years!

Check yourself with instruments, it can be probably more than 10 dB of gain and a better AGC performance. See the Level Diagram in the Service Manual.

With the FETs on the right position, we would have It would be interesting to measure these gains before the correction. With this measurement we would have an idea about the sensitivity losses due to the two errors. I laught a lot when I confirmed both errors! Almost two decades waiting to be corrected! As I never heard about this problem, I decided to reveal it to the whole world. My radio was working apparently well. This is the 1st TSS that I could observe and analyze in detail its circuits.

Kenwood TS-940S Service Manual

First I found the RF Preamp FET in a odd position, but only few days after I could focus and see that the cascode circuit was correct in the schematic diagram and wrong in the PC board.

It was also wrong in the PC board view pictures in the Service Manual. I also noticed that a FET was hotter than the other. Some FETs can be used either way around without any noticeable change in behaviour. However, most FETs are built with a channel wider at one end that the other. So, although you can use a FET with the drain and source leads swapped around, most of them don't work very well if you try it.

Therefore try to correct your TSS. Who knows that the 2SK can be swapped? The RF gain increased and the noise decreased. Very fine!

But, in the middle of the night, excited with this amazing discovery, I kept on thinking if this error was the only one.

This picture shows the FET in the correct position.

KENWOOD TS 940S MODIFS

By eliminating these "losses", my famous TSS "won" 10 dB more! Because of that, I had to made S-Meter adjustments. I suggest you to revise the famous TSS receiving performance to be even better, of course! Our next step will be identify different N-FET for replacement.

The 2SK is discontinued since Probably by using modern FETs, the receiving performance will increase.

Kenwood TS-940S Instruction Manual

Who knows? I recommend voltage measurements before and after the correction. In these pictures the FETs are in the wrong position. I can assume that thousands of other TSS are also waiting to be corrected and perform Rx even better mistakes "hidden" for almost 20 years! Check yourself with instruments, it can be probably more than 10 dB of gain and a better AGC performance. See the Level Diagram in the Service Manual.

With the FETs on the right position, we would have It would be interesting to measure these gains before the correction. With this measurement we would have an idea about the sensitivity losses due to the two errors.

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I laught a lot when I confirmed both errors! Almost two decades waiting to be corrected! As I never heard about this problem, I decided to reveal it to the whole world.

My radio was working apparently well. This is the 1st TSS that I could observe and analyze in detail its circuits. First I found the RF Preamp FET in a odd position, but only few days after I could focus and see that the cascode circuit was correct in the schematic diagram and wrong in the PC board. It was also wrong in the PC board view pictures in the Service Manual. I also noticed that a FET was hotter than the other. Some FETs can be used either way around without any noticeable change in behaviour.

However, most FETs are built with a channel wider at one end that the other. So, although you can use a FET with the drain and source leads swapped around, most of them don't work very well if you try it. Therefore try to correct your TSS. Who knows that the 2SK can be swapped? The RF gain increased and the noise decreased. Very fine! But, in the middle of the night, excited with this amazing discovery, I kept on thinking if this error was the only one.

This picture shows the FET in the correct position. By eliminating these "losses", my famous TSS "won" 10 dB more!

Because of that, I had to made S-Meter adjustments. I suggest you to revise the famous TSS receiving performance to be even better, of course! Our next step will be identify different N-FET for replacement. The 2SK is discontinued since Probably by using modern FETs, the receiving performance will increase.

Who knows? I recommend voltage measurements before and after the correction. The modifications were verified and tested by myself, so if you try this mod on your own equipment, it's on your own risk. Have fun, revise your TSS! All this can be avoided by substituting the relay with a transistor that can be mounted physically on the Remote Socket and only one resistor leg needs to be cut on the Control PCB: For use with a TL amplifier it is necessary to use a high-voltage transistor such as the MJE and a zener diode of V as it has a V DC relay coil that must be grounded for TX operation.

This modification will work on any amplifier requiring pull-down for TX. If the pull-down is only for 12V, the zener diode voltage can be lowered to 15V or eliminated all together if there is no relay. In case of damage, to replace these transistors you have to follow some tricky steps. To use low gain transistors, or to use high gain transistors different dot colors and modify the bias, etc.

In any situation you have big chances to blow up again the drivers. The first reason is because this transistors are high voltage transistors 29V We know that high voltage RF transistors has higher gain then 12V transistors, and the possibility of oscillations it is also bigger.

In the same time the design of the PA layout is not one of the best, which help to oscillate. This transistor is cheap used in most of CB radios. This could be a LM TO3 type. The input of 12V regulator was connected to 29V, from the same point where you disconnected the L7 inductor. I installed LM regulator on a small heat sink, outside of the PA compartment. Now you have to adjust the bias of the drivers. Good luck and I am not responsible for any mistakes you make!

If these transistors are installed without modifying the driver bias circuit there is a strong possibility that they will fail within a very short time frame. Recommendations: Use of Red, Orange, or Yellow hfe color rankings is recommend. These lower gain transistors work just fine and do not suffer from the circuit instability problem. During its production the TSS used two different varistor values. It was changed in mid-production to an SVYS. R15 was changed from an ohm resistor to a 1 Kohm resistor at the same time.

Therefore the countermeasure differs depending upon the serial number of the radio. After replacing the drivers check the bias current.