Kenwood 940s re-cap Part 2- KF4KQS

Ok, time for part 2 of this adventure.
We will start with the filter caps. Remove the bus wires from the old caps. Check the 4.7 K ohm resistor to be sure it’s still in tolerance. This one wasn’t.
If you don’t have the correct 4.7 K ohm @ 1/2 watt resistor, you can take four 4.7 K resistors @ 1/4 watt and wire two of them in parallel, then wire the other two in parallel. Then you take the two parallel resistor bundles and wire them in series. That will give you your 4.7 K ohms @ 1/2 watt. Wire them across one of the new filter caps, then take your two bus wires and wire the caps together. Should come out like this:

KW21

Now, since the leads on these puppies are WAY shorter than the original ones, I did some modifying to the ground lug that solders to the chassis. That is the copper strap soldered to the right ground lug. It will also give a bit more room to get the iron down inside the radio to solder to the chassis. If you don’t have any copper strap, you can use a bit of Romex wire if you’d like.

Next it’s time to start connecting the HV wires to the caps. BE SURE TO SOLDER THE CORRECT WIRES TO THE CORRECT LUGS ON THE CAPS!! You don’t want to blow up your rig!

Once the wires are securely soldered to the filter caps, it’s time to rotate them back into the chassis and solder the ground strap to the radio. Be sure to get a good flow of solder onto the strap and chassis lug.

Now that that is finished we can screw the cover back over the caps.

Carefully get the cover back into the radio making sure not to pinch any harness wires and also double checking that the wires on the caps aren’t going to short out on the chassis cover. Install the four screws that hold the cover on.

Next we will install the PS board. Carefully maneuver the board back into its place and secure it with the four screws that hold it down to the filter cap cover. Then start, one by one, reconnecting the harness wires back onto the board. Be sure they all seat correctly and that they are back in their original spots.

Next it’s time to recap the DC-DC board located under the speaker. The speaker sits on a shelf held down by four screws:

Remove the four screws and mark the three plugs that are attached to the assembly:

Then carefully unplug the harnesses and flip the entire assembly over to the right. The little board is the DC-DC board:

It is held down by two screws. There are three plugs, all of which are different, so there is no need to mark these. Remove the board. You will notice some factory modifications on the back of the board. Two jumpers, a resistor and one capacitor:

The resistor on mine checked out ok, so I’ll leave it. Replace the electrolytic on the back, and the rest on the front:

Once all the caps are replaced and all solder reheated, it’s time to reverse the process and get the radio back together.

The radio power supply has now been recapped. You will have to go through the service manual and find the voltage adjustments and go through that procedure. I did this one, but needed both hands, so pictures weren’t available.
This radio still has other problems I have to address before it will work again. Both memory batteries need to be replaced, and it has plenty of bad solder joints underneath on the IF, RF and Control boards. I will pull each one by one and resolver them at a later date, so stay tuned for part 3!

I hope you are enjoying this adventure as much as I am. ‘Till next time,
Best 73!
De,
Josh KF4KQS

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