I’m excited to bring you another project from MARC member, Josh Brothers, KF4KQS. He gives great detail and photos as he moves through his project, so I’m sure you’ll enjoy this. As a heads-up for future reference, you can go to the Projects page and find a link back to this, and others, project for easy reference. Enough of this stuff; here’s Part 1 of the Kenwood 940S re-cap from Josh.
This recap job will contain some pretty hefty “surgery” to complete. A lot of wiring will have to be pulled, and a lot of soldering will have to be done.
*** Make sure the radio has been off and unplugged for quite sometime before doing ANYTHING to the power supply! ***
-#2 Phillips head screwdriver with magnetic tip
– 25-30 watt soldering iron with a medium to small tip
– needle nose pliers
– solder wick and solder sucker
– electronics solder, about .032 diameter or so. (Larger diameter may be troublesome on the PCB).
-small wire cutters
– masking tape or labels and something to write with I.e. pen or marker
-cheap wire ties
Kenwood 940S re-cap
Kenwood TS-940S HF transceiver. This is a big heavy radio capable of 150 watts output in SSB/CW. This radio is in dire need of a power supply recap job. A total of about 20 capacitors in all.
It is best to do this job in stages so as to not get carried away and forget something or mess anything up. Great care MUST be taken when dealing with the wiring in this radio so nothing gets broken or mislabeled.
Here is the capacitor kit I ordered from Canada.
This is the main power supply board located just under the top cover. Notice all of the wires coming in and out of the board.
Be sure to label ALL of the wires either with a marker where the wire meets the plug on the board and/or tape wrapped around the wires with the plug location marked on the tape. Not doing this could leave you with some major headaches during reassembly.
Once you have removed all of the plugs and wires from the PS board and labeled them, use some wire ties to GENTLY pull the harness out of the way. Then, remove the 4 screws holding the board down. Carefully remove the PS board from the radio. Note the bulging capacitor tops. There are 10 Electrolytic capacitors that need to be replaced on this board. BE SURE TO PUT THEM IN CORRECTLY!! Installing one of these capacitors backwards will be very bad and will destroy the board and possibly rendering the radio useless.
After all of the capacitors are replaced, go ahead and touch up the solder on the rest of the board to prevent having to go back into the radio later. It should look like this when finished:
Now it is time to get after the 22,000 uF filter capacitors that are located under the chassis where the main PS board goes.
There are 4 screws that hold the metal cover onto the radio chassis. Remove these screws and again, carefully remove the cover out of the radio taking care not to strain any of the wiring in the area.
With the cover removed, you will notice two large capacitors with three large wires attached to them. These will also be replaced.
These are soldered together with some heavy gauge bud wire and then one negative lead is soldered to the radio chassis. It will be a very tight fit, and care must be taken as to not melt any of the harness when removing these caps from the chassis. Use more wire ties to pull any wiring out of the way.
This pencil is showing the ground lug on the chassis that needs to be unsoldered:
I had to use a wire tie to move some wiring out of my way:
With the caps unsoldered from the chassis, you get this:
BE SURE TO OBSERVE THE POLARITY OF THE CAPS AND WHERE THE WIRING GOES! There is also a 4.7k ohm 1/2 watt resistor across one of the capacitors you should replace while you are in here:
Since I don’t happen to have that value resistor on hand, these will have to wait until later to be replaced.
I will get the correct resistor and have part two of the recap job coming soon. There is also one other PCB that must have some surgery done to it that I will also cover in the next segment.
Until next time,
I hope everyone is enjoying the projects stuff. Part 2 is in the chute and will be posted later this week. Thanks again to Josh for sharing this project with us. What project are you working on? Whatever it is. send it over to me and let’s show it off. Your project may inspire someone else to get started on one they’ve been putting off.
73s de K5RFL!