[Elecraft] [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: Elecraft@mailman.qth.net 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
Re: [Elecraft] [K3] KRX3 Installation R91 mod
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: Elecraft@mailman.qth.net 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 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
Re: [Elecraft] [K3] KRX3 Installation R91 mod
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:w8...@comcast.net] Sent: Saturday, January 24, 2009 6:14 AM To: elecraft@mailman.qth.net 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.
Re: [Elecraft] [K3] KRX3 Installation R91 mod
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 -- View this message in context: http://n2.nabble.com/KRX3-Installation-R91-mod-tp2208918p2210460.html Sent from the [K3] mailing list archive at Nabble.com. ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
Re: [Elecraft] [K3] KRX3 Installation R91 mod
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 ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
