If you've got the right resistance across R91, you're good! Golly Dave, never be embarrassed to stumble over a problem. To paraphrase an old saying, "If you haven't damaged a trace, you haven't worked on enough pc boards..."
That pad was chosen because trying to solder directly to the IC with it's very close spaced leads is much harder, so you're soldering skills are quite redeemed for having succeeded! You bring to the group a good lesson though: work for performance, not "pretty". When reworking boards it's quite easy to get all caught up in a beautiful solder joint that looks like the original production soldering (which was done by machines on perfect boards) and end up messing about too much. In your case the only damage was minor to a trace. Too much heat can damage I.C.s and even resistors like the one shown. You don't always get really smooth flow all over the pad. All you care about is good flow into the existing solder joint. Note the left end of the added resistor. You can see that the solder there did not completely flow to the edge of the pad although it flowed well into the existing solder. Leaving it like that comes directly from experiences like yours :-) Here are few things for everyone to be aware of when doing changes like this: 1) If you notice that you're having more trouble than you recall in the past getting good solder flow, check your iron. Many temperature-controlled irons are actually measuring the temperature of the heating element and corrosion building up where the tip connects can drastically reduce the amount of heat reaching the tip. As you know, if it takes more than two or three seconds for the solder to melt, the tip is not hot enough, no matter what the temperature setting says. 2) A tiny dab of solder added to the old joint and fresh "tinning" of the new lead before trying to join them help a lot. You end up "sweating" the two fresh solder joints together when you connect and heat them. You still need a little fresh solder, but more for its rosin to deoxidize the surfaces than for additional solder. 3) Solder does not smoke. The puff of smoke that commonly rises when soldering a joint is the rosin burning away. When that happens there's no more rosin cleaning the surfaces. If the solder is molten, fine, but if not there's nothing left to clean it until you add more solder and rosin. That's why it's so easy to get too much solder on small joints and why it's so important to use fine solder. I generally use 0.015" solder for this work, and *never* anything bigger that 0.031" solder. 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 -----Original Message----- From: Dave Van Wallaghen [mailto:[email protected]] Sent: Saturday, January 24, 2009 6:14 AM To: [email protected] Cc: Ron D'Eau Claire Subject: [K3] KRX3 Installation R91 mod 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: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
