Rebuilding R-390A Power Supply Caps. Step by Step With Photos

Discussion in '"Boat Anchor" & Classic Equipment' started by KC8VWM, Apr 16, 2016.

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  1. KC8VWM

    KC8VWM Ham Member QRZ Page

    This thread is intended to document the reconstruction of R 390A power supply capacitors from start to finish.

    I haven't found any good sources explaining "how to" do this exactly with any significant level of clarity and step by step detail. So I am creating this thread as a reference for those wishing to rebuild their power supply caps in their cherished boat anchor rigs.

    This information is not only limited to the R390A, but could be used to demonstrate how to rebuild caps in any boat anchor for that matter.

    It would be great if we could all go out to Radio Shack and buy direct replacements for our boat anchors but since this is not possible, we are required to rebuild them ourselves.

    I recently picked up an R390A on the cheap. It was in good physical condition. Super clean inside but the seller said it didn't power up so I got it at a rock bottom price. With a little knowledge and know how, it is possible to save a lot of money buying non working boat anchors and restoring them to work again.

    So I brought it home and threw it on the bench to see what was wrong with it. Tried to power it up but no go. No tubes were lighting up and it appeared dead. So the first thing to check are all the fuses. I grabbed the Fluke meter and pulled all the fuses and they checked out ok.

    Then I remembered that the R390A has a quirk with the power / standby switch on the front panel. There is a micro relay switch located on the back of this switch and it sometimes sticks preventing the rig from powering on. The micro switch sticks because the relay contact arcs inside and they recommend never placing the rig in "standby" because of this quirk. So to get the micro switch working again, you have to use some old fashioned and unconventional technology to fix the problem and here is the solution...

    You simply use a small hammer and a wooden dowel stick. Yes, you heard me right. :) Now locate the power on / standby micro switch behind the panel of the R390A and rest the dowel on top of it. Give it a light tap or two and Viola! The R390A immediately powered up just like magic!

    So the result is now I have an R390A that was apparently sold to me a few hours ago as completely dead as a door nail for a $100 bucks. It is now powering up and working again thanks to Mr. hammer and wooden dowel. :)

    All the tubes were lighting up so all the modules inside the R390A were getting power. This one already had the solid state conversion done to the power supply so that's good.

    I suspect this one is also a "depot spare" rig that never seen much use at all since it was originally first decommissioned and here's why I have come to this conclusion.

    It's clean as a whistle inside! Even the gears are spotless and they have no wear on them. There is also no grease on the gears at all. Incidentally, the depot never greased any R390A gears when servicing them. It wasn't listed as part of the service schedule.

    There is still evidence of the yellow stripe on the front panel of this R390A. They did this to all R390A's when they were decommissioned from service. Most of the stripe has been removed by it's previous owner but it doesn't look like any attempts were made to do anything else whatsoever with this rig since it was acquired.

    The meters are "still missing" Again, more evidence absolutely nothing has been done with this R390A since it was first decommissioned.

    There is clear evidence it was serviced at a depot before. It has a Stewart Warner RF deck, The IF deck is an EAC. The panel has been repainted before. There is a small scratch about a 1mm in size on the bottom corner of the front panel and it was filled in and painted over and it's not a touchup job. Same goes for where screws were previosly used to hold the front panel inside a rack. Small "circle rings" are evident but were painted over. Looks like it was repainted by a depot in the past.

    The solid state conversion to the power supply module has already been completed. The rectifier installed inside is "green" military grade with military numbers stamped on it and it's been "professionally" wired and mounted to the chassis. The old tube rectifier holes in the power supply have been plugged and the entire solid state conversion looks far too professional to be anything else but a depot repair service job.

    I also have an "original" copy of the R390A manual. It is not a reprint, but 100% original. The only place an original manual for an R390A would come from is a service depot. This also suggests the rig was stored inside a building along with the manual which is in the same physical condition as the R390A itself.

    So moving along I powered up the R30A hooked up an antenna and my 600 ohm headphones to the phone jack on the front panel. I tuned it into to listen to WWV. I noticed the the frequency display was right on the money. Then I tuned around and heard brother Stair :) Put it on 40m and played with the BFO on SSB signals and listened to a few DX'ers calling CQ. So it seemed like it worked. :)

    However after a few minutes a "hum" was noticed in my headphones. I tapped on the power supply caps with my wooden dowel stick and this would make the hum disappear and come back again. So it was evident the power supply caps must be leaking and in need of replacement.

    Of course they are probably quite old and need replaced anyways. If you don't do anything else with your R390A, at the very least you should rebuild the power supply caps.

    So let's get started rebuilding the power supply caps shall we? .:)

    These caps are located on the AF chassis on the bottom of the rig. Marked on the AF module as C 606 and C 603.

    R390a caps_zpsgys3uf7f.jpg
    Last edited: Dec 4, 2017
    W5INC, KD2JPO, AF6LJ and 1 other person like this.
  2. KC8VWM

    KC8VWM Ham Member QRZ Page

    Lets start by removing the AF deck located on the bottom of the R390A

    There are 4 green colored screws on the corners of the module indicated by the green arrows in the photo.

    Disconnect the two wiring harnesses from the AF deck marked as J 619 and J 620.

    Grasp the connector shells with your fingers and avoid the idea of pulling them off using the wire. The connectors might be stuck a little so just wiggle and rock them back and forth to get them off.

    AF deck_zpsz06jsyne.jpg

    The green screws holding the deck to the chassis cannot be completely removed from the deck, they have retainers attached on the screws to keep the screws there. Just loosen them enough so the deck will slide out of it's chassis.

    After removing the deck from the chassis you will be left with this...


    ( Pretty clean inside there huh? :) )
    Last edited: Dec 4, 2017
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  3. KC8VWM

    KC8VWM Ham Member QRZ Page

    When removing the deck be careful where you put your fingers. Do not let them touch anything on the underside of the chassis. Remove and carry the deck to the bench using the two big square transformers at the top.

    Place the deck on the bench and remove the capacitors. They are held to the deck by a single screw.

    Do not under any circumstances touch any of the pins on these plug in capacitors!

    In fact, immediately after they are removed from the deck they must be discharged.


    Discharge them by touching ALL the pins of the capacitor to your station ground, or to a ground rod outside.
    Last edited: Dec 4, 2017
  4. KC8VWM

    KC8VWM Ham Member QRZ Page

    Once the capacitors have been discharged bring them back inside and remove the clamps from them.


    Place the capacitor clamps and screws back on the deck so they won't get lost. :)
    Last edited: Dec 4, 2017
  5. KC8VWM

    KC8VWM Ham Member QRZ Page

    Next locate the edge of the capacitor can where it meets and transitions to the plug assembly near the bottom of the capacitor.


    Next we are going to use a Dremmel tool with a cutting wheel attached, set to around speed #12 to cut a "clean line" along this edge for the entire diameter of the capacitor.


    Think of it like you are using the Dremmel tool as a can opener. :)

    Last edited: Dec 4, 2017
  6. KC8VWM

    KC8VWM Ham Member QRZ Page

    Once the clean line is cut around the bottom of the capacitor you must pull off the plug from the rest of the capacitor can.

    This can sometimes be difficult because there are metal rods that extend from the plug pins that are glued into the black tar mystery goo that's inside the capacitor can.

    However with some perseverance, wiggling back and forth and a few swear words this plug will break free of the main capacitor can and you will be left with this piece in hand



    Now it's time for a well deserved break. :) I'll be back to explain how to remove the black tar mystery goo from inside the capacitor can.
    Last edited: Dec 4, 2017
    KE5OFJ and K9ASE like this.
  7. KB4MNG

    KB4MNG Ham Member QRZ Page

    Great thread, very interesting. I always take the option of mounting the caps under the deck and not cut the caps...
    KD2JPO and KC8VWM like this.
  8. KC8VWM

    KC8VWM Ham Member QRZ Page

    Thanks for the comments. :)

    I have also taken this approach when replacing caps before too. But it usually depends on the equipment you are recapping.

    Power supply capacitors in particular can generate a lot of heat. This means they need a lot of physical clearance around them to dissipate the heat they generate.

    Installing them in direct proximity or even touching any wiring or other components like resistors may cause other unintended issues.

    Rebuilding your caps is also the more preferable route to take if you are trying to maintain the equipment in as original condition as possible.

    However, in this particular case it is actually necessary to rebuild the original power supply caps. The clearance available from the very top of the AF deck to the bottom where it meets the chassis of the R-390A is 1".


    Because of the rather restricted and limited space available on the bottom of the AF deck of the R-390A. There's simply not enough physical room to accommodate 5 rather bulky HV capacitors and therefore the original caps must be rebuilt. :)
    Last edited: Dec 4, 2017
  9. K8CCA

    K8CCA Ham Member QRZ Page

    If ya wanna double your money, I am your guy lol
    KC8VWM likes this.
  10. KC8VWM

    KC8VWM Ham Member QRZ Page

    Well he rolled it into the hamfest on a push cart, set it down on the table and started the sale as a "non working" R-390A with a sale price of $250

    The second day of the hamfest the $250 price was crossed out and it was marked down for $200

    By the end of the hamfest, he was going to throw in another non working Hammarlund receiver and the R-390A both together for $150.

    I threw $100 bucks down on the table just for the R-390A and I walked away with it.

    I had it powered up and was listening to station WWV in less than 3 hours after loading it into my car. :)
    Last edited: Apr 17, 2016
    K8CCA, WB4WHJ, AE5DX and 1 other person like this.

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