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W4JBM's Hints and Tips

I've always loved those little bits of information that make working on radio and electronics easier. I remember when I was a kid, I built a small project on a very tight budget. It was housed in a small cabinet made of wood. I didn't have any feet for the project and the prospects of talking my mom into a trip to Radio Shack and out of the money to buy rubber feet seemed unlikely. I was looking through some old issues of QST, and in the Hints and Kinks column was a suggestion for cheap feet--the caps off of used toothpaste tubes. I brushed my teeth several times a day for the next few weeks and saved my caps. When I finally had four of them, I carefully drilled holes in the center and mounted them. And it looked--okay, well it looked like I'd used toothpaste tube caps for feet. But it sounded like a good idea...


One hint that I've found useful over the years is a way to clear the hole on a printed circuit board of solder so you can easily insert a replacement component. A lot of people use "solder suckers" or solder braid--and a lot of people wind up lifting traces off the circuit board. But a simple toothpick will do the trick. Heat the pad, insert the toothpick, then remove your soldering iron. After the joint cools, remove the toothpick and you'll have a hole clear and ready for the replacement component.


A lot of mass produced stuff is held together with rivets. It's not that intimidating to have to drill out a rivet and replace it with a bolt and nut--but sometimes it's harder than it looks. The sides of rivets are smooth and when you start to drill them out, they may start to spin in the hole.

If this happens, tilt the drill slightly to one side. Now as the rivet spins, you begin eating away the material on the lip. Just slowly tilt further and further to the side until the lip has been removed and only the shaft of the rivet remains. Push it out and you're in business...


Once I was trying to clear the solder terminals on a open-frame transformer. Using solder wick still left a fairly thick coat of solder on, so I decided to use a small, circular file to clear the solder. I put it in a chuck on my electric screwdriver and it did a great job--except every once in a while it would grab and (because of the way the groves were cut on the file) 'screw' into the terminal. After this, I'd have to spend some time working it back out.

It finally occurred to me to reverse the electric screw driver. Now the file tended to 'push out' instead of 'pull in'. I was able to quickly clear all the solder terminals.


If you have a small transistor radio that seems to eat batteries, you might want to check the on/off switch on the volume control. I once came across one that was stuck on. The volume was low (and the switch would seem to click into the off position), so there was no sound from the speaker. But it was constantly drawing current. I just happened to find it when I hooked it up to a the bench supply and saw that current was flowing even when the radio was "off".


A lot of techs have damaged boards trying to remove 40 or 24 pin chips. Heck, I've even lifted traces replacing 8 pin chips. Most of these chips only cost a buck or two. If you think about what a technician costs an hour (or what your time is worth), there isn't any point in taking an hour (or two or three) trying to carefully remove it.

Back when I was in college, I worked as a tech in a computer store. Once when I was about an hour into removing a bad 40 pin CPU chip the other technician said he'd show me a quicker way to do it.

He grabbed the board, set it on the bench, and covered it with a couple of rags so only the bad chip was showing. Then he got the Dremil tool with the cutting wheel and carefully ran it along the sides of the chip. That cut all the pins free and he handed the chip to me.

Then he got a pair of forceps, latched on to the top of one of the pins that remained on the board, touched the other side with a soldering iron, and pulled the pin out. He had all 40 pins out in two or three minutes.

There was still solder left on the board, so he used the desolder station to clear each hole.

In about five minutes, he'd done a job that would have taken me hours. And it's likely I would have lifted a few traces in the process and had to fix those when I installed the socket.

I've used this process hundreds of times since. In some of today's dense circuit boards I'd rather use dikes to cut the leads free if I can (and not risk the metal filings the Dremil can make). If I'm in a hurry or don't have a desoldering station (like when I'm doing field repairs), I'll even use this method to remove a resistor or capacitor that's gone bad.


It's always amazed me how many 'broke' pieces of electronic equipment can be fixed with a good cleaning and wiggling of parts. Over the years, probably 50% of the 'hard' failures and 90% of the intermittent problems I've worked on are fixed without changing a part.

I use a lot of rubbing alcohol and cotton swabs. Sometimes the cotton swabs aren't a good choice. If there are sharp points the cotton may pull lose.

Make sure you clean all the dust and lint that tends to accumulate out. Pull the removable cards out. Clean the edge connector (both on the card and where it plugs in). If there are chips in sockets, reseat them. (You'll almost always hear a 'creak' as you push on the chips--just shows they were lose.) Make sure all the ground connections are good. If they cards are screwed down once they are seated, use a lock washer to get a solid electrical connection.

At one point I managed a repair shop and our customers were always happy with our prices. The secret was having a couple of trained people do the cleaning prior to passing units to a technician. An hour of a cleaner's time was about half as expensive as and hour of a tech's time. The cleaner's also didn't need a bunch of expensive test equipment on their bench. Our average repair cost (in the mid-1990's) was around $35, while our competition had minimum charges of $50 or $75.


Need to change out a transistor or diode in the field and you don't have a heat sink? It sounds kind of silly, but putting a paper clip on the lead before you begin soldering will protect the device. It's not as good as a regular heat sink, but I've tried this several times and never lost a device doing it.


How many times have you torn something apart and then be left to wonder about some small detail when you went to put it back together? How was the string on the tuning dial ran? Which way was that spring installed?

Digital cameras have become popular--and reasonably priced--lately. These are great for documenting how things are found. You can take a dozen pictures and just save them on disk. If you need them later, you have them. If no, delete them.


I was recently involved in a field test program where we needed to run about 1,000 feet of coax cable between various point. After all the trouble we had keeping the 100 foot cables from getting tangled, the thought of unrolling 1,000 feet was kind of intimidating. The answer was found in the shape of one of those hose reels available at the hardware store.

The 1,000 feet went on with no hitch. One word of warning. Anyone who does much fishing knows that backlash can make for a nasty tangle of fishing line. You can have that same problem with this real. Keep tension on the cable as you reel and unreel it. Don't try to go too fast. It takes far longer to untangle the mess caused by a backlash than to just walk the 1,000 feet.


1000 feet of coax...

Here is about a thousand feet of RG-58 coax stored on a hose reel...

200 feet of coax...

If you don't need that much coax, here is about two hundred feet stored on an extension cord reel.


There are a variety of connectors that can be used with coax cables. My favorite crimp-on is the F connector commonly used with cable television (CATV) systems. It's cheap, easy to find, and easy to install.

One thing to be careful of with a lot of CATV cable is that the center conductor is not copper. Rather, it is stainless steel clad with copper. When stripping cable, it is important to not nick the center conductor. A nick can cause a discontinuity that shows up at higher frequencies. This can be avoided by using a stripping tool instead of trying to strip the cable with a knife.


I've used LEDs as pilot lights on lots of projects over the years. I typically had bought those nice chrome holders to put them in. I figured this would make it easier to replace when it burned out. In all honesty, I've never had an LED burn out. (Burn up, yes. But that's a different story...)

I finally tried the low cost plastic clips that Radio Shack has to hold LEDs. I didn't think I'd ever get that thing to fit in the hole. After a bit of struggling, I found a way that made this much easier. I took a nut driver that was large enough for the LED to fit up in easily, but small enough that the holder wouldn't. I then used the nut driver to press the holder and LED into the panel hole. This worked great!


Around the shack, I have several sets of headphones, external speakers, etc.. I have various adapters to hook these to different things. The problem was that I couldn't keep all the adapters straight. For example, the adapter to connect my 1/4" phone plug to a 1/8" plug looks just like the adapter that connects my stereo headphones (with a 1/4" stereo plug) to a 1/8" plug.

After having to test things with an ohm meter a couple times, I decided to use a color code. Now any adapter that accepts monouaral plugs has a band of blue tape and any that accepts a stereo plug has a band of green tape. I've also put bands around the plugs so I don't have to remember the color code--I just pick up the headset I want to use and plug it into an adapter with the same color tape.

Once I got everything straightened out and marked, it's worked great.


If you're wanting to practice Morse code and need a cheap practice oscillator, here's the easiest I've found. I turned on the continuity test feature of my digital meter, connected alligator clips to the key, and I was in business! I did find that I had to turn off the autorange function--otherwise it took a few seconds for it to range from the highest ohms scale (open circuit) to the lowest (a short).


I had trouble getting the insulation off of the enamel wire used in coils for years. Scraping with knifes seemed to lead to nicked wires. I used a fine sandpaper for years, but still wasn't happy with the results. Then I saw someone recommend using your soldering iron to burn off the insulation. After a few tries, I got this process down...

For most coils, I try to unwind it a bit so I've got some room to work with. I attach one of those clip on heatsinks (like you can pick up a Radio Shack) to the point where I want to stop stripping/tinning the wire. I then position things so the end of the wire is at a downward slope from where I have the heatsink attached.

Now I put my soldering iron on the cut end of the wire, add plenty of solder, and slowly work my way up the wire. As the enamel burns off, continue adding some solder. When the 'blob' gets too big, take a break to clean the tip and start again where you left off. Once the enamel is removed up to the heatsink, I usually clean the iron and starting from the heatsink 'tin' the wire down to the end.

CAUTION: Do this in a well ventilated area. I suggest using a fan to keep fresh air moving across the workspace and to keep the smoke and fumes moving away from you instead of up toward your face.

I've seen other people suggest similar methods and talk about having mixed success depending on the type of wire they're using. I think most people tend to start removing the enamel at the top of the wire (where I put the heatsink). If you do this, you have to boil off the initial enamel and then things go fine. But sometimes this is hard. My hypothesis is that by starting at the clipped end of the wire, you have access to the copper itself (even if it's only an area the size of the wire's cross section). When you apply the solder here, it seems to work up under the enamel and quickly boil it off. I've consistently had good results with this method.


I typically use traditional transformers when building power supplies for my projects, but a while back I bought several toroidal transformers at a hamfest. To mount these, you typically use a piece of solid material (I've used cut up CD jewel cases) and a piece of rubber material (I use some foam stuff from the craft store that is specified as being non-flamable) to 'sandwich' the transformer. You then bolt the assembly to the chassis. One thing I've been warned about is making sure the bolt is either non-conductive or that it is insulated from the chassis at one (or both) ends. What you want to avoid is having a 'loop' through the center of the transformer. This will look like a shorted turn and cause problems. I haven't personally had this problem, but was warned by someone who experienced a great deal of difficulty with a homebrew power supply because the toroidal transformer was sandwiched between the chassis and a PCB which were both at ground.


I'll be adding more as I can. If you have a favorite hint you'd like to share, e-mail it to me.


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