HAM TO HAM - #2

Conducted by Dave Miller, NZ9E

In last month's issue of 73 Amateur Radio Today we inaugurated a new column, Ham To Ham, with yours truly as conductor. In HTH, we looking for interesting ham radio related tips, techniques, equipment modifications, workshop shortcuts, just about anything that would be interesting information to pass on to others, young and old alike. We very much need your input to keep the column vibrant, so jot down your ideas or discoveries and send them to me at:

73 Magazine's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

73 Magazine will generously pay you $10 for each idea that's published in this column, plus you'll be helping countless other hams worldwide who can benefit from your experiences. Every legitimate idea will be promptly acknowledged, and the author will be given an idea whether his or her tip will in fact be used in an upcoming column. We're looking for original ideas and suggestions, ones that haven't been published before and have been successfully used by the author - or others - and can be duplicated by our readers in their own station setups.

We also invite any comments on the column as well as suggestions on its direction and content. What format would be most valuable to you, the reader? Do you want strictly technical tips or a combination of both technical and operating ideas? Is the conversational style most helpful, or simply editing and printing each tip individually, with it's own bold heading followed by the tip, then the author's name and call? This is your column, so be sure to let me know how you would like to see it conducted, your comments will be extremely helpful in establishing the guidelines of this new medium of information interchange within 73 Magazine's pages...let's keep it Ham To Ham.

Too Much Trust?

We all tend to trust new parts a bit too much, I know I'm guilty of the same naivete at times. When I set out to build or repair some item of ham gear, I inevitably assume that the new parts that I'm using are good, will operate as advertised and will provide long life. The vast majority of the time, that procedure works just fine. Besides, what else can one do?

A friend of mine works for a manufacturer of electronic control panels, and they use lots and lots of off-the-shelf electronic parts every day. He has come across diodes with the cathode band imprinted on the wrong end (the anode end), resistors whose color codes don't always denote the actual value of the resistor and capacitors that are either misidentified or - for some reason - are open or even shorted, right out of the box! Just about every electronic part problem possible is experienced by any large manufacturing firm dealing in electronic circuit construction.

Please don't misunderstand, these abnormalities aren't necessarily everyday occurrences, but they can and do happen fairly often when dealing with tens of thousands of parts in the "real world" of electronic manufacturing. Here's the point of all of this, it pays to check the parts you'll be using in your next pet electronic project, before committing them to use, even if they're "brand new". And always check any parts that even appear to be suspicious, before installing them in the circuit. It's so much easier to check a part before soldering it in place and it's so much wiser to eliminate any problems before applying power to the circuit, possibly damaging more perfectly good parts.

So why don't we always do it? It's pretty boring stuff, checking parts ahead of time. It's also much more fun to just go ahead and build the circuit, hoping for the best. How much can you check and double-check, why not just put it together and save the "smoke test" for last? Of course, it's up to the individual, but after hearing some of my friend's findings in his commercial experiences, I'm far more inclined to check parts first now, especially if the circuit is critical, easily damaged by defective surrounding parts or looks like it will be particularly difficult to troubleshoot when it's done. It does take more time, to be sure, but it can also save time and dollars in troubleshooting later on. At least if you know that all of the parts were within their specifications to begin with, even if the circuit doesn't quite work as it should when fully assembled, you have the knowledge that the parts probably weren't the main problem initially. The small amount of self-discipline needed to pre-check the main parts - especially those whose markings or color codings might be questionable from the start - will often pay big dividends in the successfulness of the end results. It's one of those things that seems obvious, yet few of us actually do it regularly.

The Case Of The Non-Insulating Adhesives

Here's a really sneaky little gremlin that can creep into your electronic circuit boards, completely unnoticed! On several troubleshooting expeditions, I've encountered the adhesive mixture - the adhesive used in some equipment to hold parts down on the foil side of the PC board - becoming semi-conductive!

It's something that you wouldn't normally expect to happen, but it appears that some of these adhesive compounds tend to dry out over time. The condition can often be accelerated by the wide temperature variations that are encountered in mobile installations, but it can also occur in home-based equipment as well. As the adhesive dries out, it can become hydroscopic, picking up moisture from the air, which can then result in the adhesive compound itself becoming partially or semi-conductive. When bridged across the conductive pads on the foil side of a printed circuit board, this semi-conductive substance can wreak havoc on high impedance circuits with which it comes in contact. PLL feedback loops, high impedance oscillators and high voltage circuits are just a couple of examples of circuitry that can be profoundly affected by semi-conductive adhesive compounds.

I've also seen a few of these adhesives apparently change molecularly, eating through the colored protective board coating and then becoming semi-conductive so that they result in high to medium impedance short circuits. This can occur even if the adhesive is seemingly on top of the board's insulating coating. If the adhesive mixture is slightly acidic and left unaddressed, it could eventually even etch through the copper traces themselves.

When such insulating property changes are even suspected in a piece of malfunctioning equipment of yours, it would be advisable to remove all of the old adhesive compound from the foil side of the board as completely as possible, and then to clean up the surrounding area of the board as best you can before proceding with any other troubleshooting procedures, being careful not to damage the board any further than it may have already been affected. If you choose to apply another type of adhesive on the foil side of the board, be sure to pick one that you know will not wind up presenting you with the same or similar problem several years down the road.

Check For Loose Screws

Over a number of years of troubleshooting odd problems in ham-band equipment from various manufacturers, I'm still amazed at how many problems can often be solved by simply checking the tightness of the little philips-head screws that hold down the various individual boards in these radios. The equipment manufacturers will often use the mounting screws as pressure ground connections at the edges - or even sometimes in the middle - of a circuit board. If the board happens to have RF circuitry on it that requires a short, direct chassis ground connection, the loss of even one screw-hole pressure ground point can cause some very strange - often intermittent - problems to develop. Problems that defy most of the normal troubleshooting techniques.

I've sometimes failed to check this point myself, or a board may be hidden somewhere out of sight behind a wiring harness, and I've ended up spending many wasted hours of tracing down dead-ends, when all that I really needed to do was to make sure that those numerous little mounting screws were nice and snug.

Since quite often soldering flux from the factory wave-soldering machine will be deposited over the grounding pads on the foil side of these boards, there can often be times when it pays big dividends to just loosen the screws slightly, then re-tighten them, hopefully breaking any insulating barrier. It may not even be a total insulating barrier, just a high resistance ground connection, but where RF is concerned, even a higher than normal resistance ground will often cause unpredictable and frustrating problems.

At times, I've had to actually clean the grounding pads with a flux remover to restore proper pressure ground connection on some PC boards. Acetone and lacquer thinner will also work, but be sure to observe the exposure precautions and fire hazards on the labels. The use of toothed lockwashers under the mounting screws in critical areas is also sometimes advisable, just make sure that you don't lose any of the lockwashers "somewhere in the works" when removing the screws at a later date. You can indicate which screws have lockwashers under them by a small "star" drawn next to the screw with a permanent,sharp, felt marker pen.

So next time you experience some inexplicable problem in your radio, try the screw-tightening routine first. Good soild board-grounds are especially important in ham mobile equipment to protect against internal grounding problems due to both vibration and to the drastically changing temperature and humidity conditions often found inside of the mobile environment.

That's all for this month, but we'll be back next time with more tips, techniques and suggestions in Ham To Ham. Don't forget to send in your ideas to the address shown above and we'll publish half-a-dozen or so of the better ones in this column each month, plus send you ten of Uncle Sam's greenbacks for your time and trouble!

73, DE Dave, NZ9E

Note: The ideas and suggestions contributed to this column by its readers have not necessarily been tested by the column's moderator nor by the staff of 73 Magazine, and thus no guarantee of operational success is implied. Always use your own best judgment before modifying any electronic item from the original equipment manufacturer's specifications. No responsibility is implied by the moderator or 73 Magazine for any equipment damage or malfunction resulting from information supplied in this column.

Please send all correspondence relating to this column to 73 Magazine's Ham To Ham column,

c/o Dave Miller, NZ9E, 7462 Lawler Avenue, Niles, IL 60714-3108, USA. All contributions used in

this column will be reimbursed by a contributor's fee of $10, which includes its exclusive use by 73

Magazine. We will attempt to respond to all legitimate contributor's ideas in a timely manner, but

be sure to send all specific questions on any particular tip to the originator of the idea, not to this

column's moderator nor to 73 Magazine.