KRX3 Installation R91 mod

[Dave Van Wallaghen]

Hi all,
At first, I was only going to contact Ron with this as I was too
embarrassed to reveal that I had maimed the RF board on my K3. But, I
then thought maybe someone else could benefit from my experience and
public humility ;-)

I have an early serial number #338 and needed to make the modification
to R91 on the RF board as described on page 21 of the KRX3 Installation
Manual. In doing so, I was having a hard time getting the 27 ohm
resistor lead to tack onto the (looking at Figure 20) right pad of R91.
I made multiple attempts and couldn't get a clean connection until I
eventually lifted the pad. I was using a small but short soldering tip
at 720 degrees. In my zeal to get a nicer connection, I simply played
around with it too long and with too much heat, lifted the pad. Using a
longer, narrower tip (as I am now) would probably have worked better.

After the horror and high emotion subsided, I sat down to figure out
what could be done and hence a question as to my solution. Looking at
the schematic for the RF board, it looks like the only connection to the
right pad of R91 is pin 14 of U7. Does that seem correct to anyone else?
I removed R91 and was able to solder a 22 ohm 1/8 watt resistor to the
remaining trace of pin 14 of U7 and the pad next to R91 as outlined in
the directions. DMM measurements between U7 pin 14 and the left pad of
R91 show 22 ohms, so I'm pretty sure I was able to salvage the situation.

I will continue with the installation this morning, but would like some
concurrence that what I've done looks correct to someone else's eyes
before I power this beast back up.

BTW - Since I was going to install the KRX3, I decided to make the mods
for the K3 Synthesizer ALS, Rear RS232 and Audio RF mods, K3 Amp Output
Mod and the Front Panel Mic Mod. Having to somewhat disassemble the unit
for the KRX3 anyway made doing these mods very simple. And as usual,
Ron's documentation for these mods was nothing short of excellent,
including some nice tips for lining things back up to guarantee all
connectors and boards line up the way they are supposed to. As usual, my
impatience leads me to push ahead of the text to get the job done, but
if you follow everything Ron has written you will be guaranteed success.

Also, in my original K3 installation manual, the first KSYN3 board was
not mounted with split lock washers on the non-component side of the
board. Since I made the mod to it, I did remount it with the split lock
washers as described in the KRX3 manual. I assume there is no problem
with that?

Now, back to work...
Dave W8FGU

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[Bill N2BC]

Dave Van Wallaghen wrote:

> Hi all,
> At first, I was only going to contact Ron with this as I was too
> embarrassed to reveal that I had maimed the RF board on my K3. But, I
> then thought maybe someone else could benefit from my experience and
> public humility ;-)
>
> I have an early serial number #338 and needed to make the modification
> to R91 on the RF board as described on page 21 of the KRX3 Installation
> Manual. In doing so, I was having a hard time getting the 27 ohm
> resistor lead to tack onto the (looking at Figure 20) right pad of R91.
> I made multiple attempts and couldn't get a clean connection until I
> eventually lifted the pad. I was using a small but short soldering tip
> at 720 degrees. In my zeal to get a nicer connection, I simply played
> around with it too long and with too much heat, lifted the pad. Using a
> longer, narrower tip (as I am now) would probably have worked better.
>
> After the horror and high emotion subsided, I sat down to figure out
> what could be done and hence a question as to my solution. Looking at
> the schematic for the RF board, it looks like the only connection to the
> right pad of R91 is pin 14 of U7. Does that seem correct to anyone else?
> I removed R91 and was able to solder a 22 ohm 1/8 watt resistor to the
> remaining trace of pin 14 of U7 and the pad next to R91 as outlined in
> the directions. DMM measurements between U7 pin 14 and the left pad of
> R91 show 22 ohms, so I'm pretty sure I was able to salvage the situation.
>
> I will continue with the installation this morning, but would like some
> concurrence that what I've done looks correct to someone else's eyes
> before I power this beast back up.
>
> BTW - Since I was going to install the KRX3, I decided to make the mods
> for the K3 Synthesizer ALS, Rear RS232 and Audio RF mods, K3 Amp Output
> Mod and the Front Panel Mic Mod. Having to somewhat disassemble the unit
> for the KRX3 anyway made doing these mods very simple. And as usual,
> Ron's documentation for these mods was nothing short of excellent,
> including some nice tips for lining things back up to guarantee all
> connectors and boards line up the way they are supposed to. As usual, my
> impatience leads me to push ahead of the text to get the job done, but
> if you follow everything Ron has written you will be guaranteed success.
>
> Also, in my original K3 installation manual, the first KSYN3 board was
> not mounted with split lock washers on the non-component side of the
> board. Since I made the mod to it, I did remount it with the split lock
> washers as described in the KRX3 manual. I assume there is no problem
> with that?
>
> Now, back to work...
> Dave W8FGU
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
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>
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>
>
>  

Hi Dave,  I installed my KRX3 just yesterday.  No problem at all adding
the washers to the KSYN3 board - it 'looks' much better with the
additional spacers - now it sits parallel to the shield.

My K3 is a bit newer than yours (S/N 00929) and fortunately already had
the proper resistor on the RF board.  I was not looking forward to
making that change.

I will pass along one observation - you will get into this when you
place the KRX3 board into the lower half of the shield box.   There are
break-off tabs around the perimeter of the KRX3 board. These are
supposed to line up with holes in the side of the lower shield.  The
tabs on the left side of the KRX3 are no where near the holes....  left
= as the board will sit in the K3.   Reading further along in the
instructions it mentions filing the tabs as needed to ensure the board
does not cause the sides of the lower shield to expand too much & mess
with the fit of the upper half.  I ended up filing ALL the tabs flush.  
After noting that the tabs on the left did not match the holes, I filed
them off and proceeded to fit the board into the lower cover. I felt it
was just too tight, in fact had a heck of a time getting it out.  After
filing all the tabs flush it was still a snug fit, but the top cover
went on perfectly.

Another minor hitch...  cycle the K3 power after you enable the KRX3 and
update the firmware.  I really don't know if it was the KRX3 enable or
the KDVR3 I installed at the same time, but my K3 went a little batty
after loading the DSP2 firmware & a power cycle fixed it right up.

Oh - don't forget the mod to the KSYN3 board, my original board needed
the mod!   Easy one, no SMT!!    (smile)..

I did have one minor encounter with Mr. Murphy of Murphy's Law fame.  As
I started to learn and listen on the KRX3, I gave the AF gain a twist
and the knob split in half.  I found a knob I had salvaged from a Tek
scope years ago that is a perfect fit, but someone (me) had robbed the
setscrew & of course the ones in the K3 knob are different.  But the
crazy glue is all set up and I'll start my learning today!

Best 73, Bill  N2BC
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[AC7AC]

CONTENTS DELETED

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[Rich]

Ron's 3rd hint is very important!  Keep some handy.  Put some on the solderwick when trying to remove components or clear holes. If that little spool of solder wick is more than a few months old the flux in it has dried out and all you are doing is heating the board/lifting the pad. I don't know how kosher it is but I keep a tin of rosin-flux paste and dip the tip of the iron it and then re-dress the tip at the start of each evenings work. It seems like these newer plated tips (that you find on the temp-controlled models) don't hold their tinning and get a build up of invisable corrosion. With the older copper tips it was quite obvious they needed re-tinning.  


*** Don't use plumbing solder paste on your PCB.  ***


Rich,
KE0X

Ron D'Eau Claire wrote

3) A very small amount of rosin is very handy if you want to avoid adding
solder. Rosin pens that dispense a tiny drop are perfect for this but even a
bottle is fine if you use a tooth pick or bit of wire to add a drop just
before soldering. Rosin in pens and bottles are available from many on-line
resources and (for the lucky ones with one nearby) most electronics supply
houses.

Ron AC7AC

[Dave Van Wallaghen]

Thank you all for the great suggestions. The rest of the installation
went well except for one hitch that Bill had mentioned about the tabs on
the KRX3 PCB. In my case, I tried to get it to fit but found that all of
the tabs running from the front to back (right and left sides looking
from the front of the K3) were offset by almost 1/8" to the rear. All of
the other tabs (front and rear) matched just fine in the shield. I filed
the side tabs down and everything fit FB.

The setup went without a hitch and I'm sitting hear playing with it and
wishing I had a vertical outside right now to play around with some
diversity reception ;-)

Thanks again for the suggestions and hopefully this thread will help
someone else down the road.

73,
Dave W8FGU

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