Mark Ward of WTSN(AM) in Dover, N.H., writes on the subject of Sage Endecs. In a previous column we published a tip that Sage Endec memory batteries were coming up on 10 years of age and should be replaced. Installation of fresh batteries would eliminate the need of reprogramming the unit should the batteries and AC power fail.
(click thumbnail)Fig. 1: Replace electrolytic capacitors every five to seven years.
Mark offers another important reminder. If the memory batteries are 10 years old, so are the (wall-wart) power supply filter caps. After he replaced the memory battery, Mark's Endec went into an endless loop of "self-tests" after power-up. Sage tech support advised that this was a symptom of excessive power supply ripple.
A new supply is $55 from Sage via Harris. Mark located a Radio Shack supply that should work, but he thought that there must be a less expensive way.
Mark's solution was carefully to cut with a hacksaw, along the seam of the wall-wart and pry the case open. Inside, Mark discovered a transformer, fuse, two diodes and a 2200 uF/25 V radial cap that had been toasted to a golden brown from its original aquamarine blue. Fig. 1 shows both radial and axial electrolytic capacitors.
Replacement of the cap with one from shelf stock restored the Endec to normal operation, and the case was closed with two cable ties.
If your technical budget is tight or non-existent, you might want to consider Mark's solution. Mark Ward can be reached at email@example.com.
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Electrolytic capacitor replacement should be automatic every seven and 10 years. In audio gear, the annoying hum will signal the bad caps. In audio processors or exciters, capacitor failure is more pronounced, producing whistles and bizarre operating behavior.
I remember a question on the FCC license examination: "Which component has the highest failure rate?" Answer: the electrolytic capacitor.
Mark's experience leads us to an important troubleshooting tip: When a piece of gear isn't working properly or behaves in a strange manner, check the supply voltages first. Measuring the voltage with a scope will show you excessive AC ripple, caused by bad power supply filter caps.
Don't have a scope? With the equipment powered off, clip-lead an electrolytic of similar size across the suspected power supply cap.
Two things to remember here. First, the working voltage of the replacement capacitor must be as much or greater than the one it will be replacing. Also, for this test, the "new" capacitor must be connected in parallel with the old one. This is, "+" to "+" and negative to negative.
Turn the unit back on, making sure the clip leads aren't shorting before applying power, and see if the problem goes away. If it does, your power supply capacitor is bad; replace it, and any others.
When one electrolytic goes bad, the others won't be far behind. Shotgun replacement of all power supply electrolytics is a good practice. Like Mark, make sure you have a good stock of replacement electrolytics. Kits are available from Mouser and Digikey with the most popular values.
Also remember these devices pack a charge. Once you've unplugged your equipment, make sure you short the leads before touching. Throwing a charged electrolytic to a college classmate in electronics lab was always a good way to wake someone up. But depending on the size of the capacitor, the charge can be deadly, so beware.
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(click thumbnail)Fig. 2: Supervise tower work to prevent this kind of damage.
Fig. 2 shows a good reason to supervise any tower work done on your tower, even if it's the installation of a temporary line. Funny how the word "temporary" is a synonym for "permanent" in the broadcast world.
Not only were hangers missing in this case, but the crimp in the line weakens it - to say nothing about the reflected power issue.
Take the time to walk your tower site before inclement weather sets in. Inspect everything. If you have a digital camera, snap pictures; the visual record could be valuable later on.
And how do you keep riggers from cutting corners like this? Tell them at the onset that you'll be inspecting their work.
I had a friend who was given an old climbing belt. He kept it in his trunk, and pulled it out when the tower riggers began their work. Whether it was a paint job or work on the tower, he intimated that he would be climbing to inspect the work. He never climbed a tower, to my knowledge; but he never had problems with work being done improperly on his towers.
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(click thumbnail)Fig. 3: Keep the tools at home as you travel by air to the convention.
Off to the NAB Radio Show in San Diego? If you plan on bringing carry-on luggage, watch what you pack.
Keep the tools at home, as well as "weapons" like cans of Adkins Shakes! Better yet, with the reduction of lost luggage claims, check your bag and eliminate the hassle.
Don't lock the bag, though. If the TSA inspectors see that wrench or hammer on the X-ray, they'll want to get inside your bag for a further look. They will break your lock to get inside. Also keep in mind that film transported in checked baggage can be fogged. Carry your film with your camera bag, and have it hand-searched.
OK, so you forget that your prized screwdriver or pocketknife are traveling in your shirt pocket, and you get nabbed as you pass through security. Rather than have the tool relegated to the trashcan, ask to check it.
Yes, you'll have to leave the security area, go back to the ticket counter and use one of the airline's small parcel bags or boxes, then pass through security again; but you won't lose your tools. The airlines will "check" these small items as baggage, so there's no charge, just the added time. But then, that's why you arrive two hours before your flight.
As you plan your NAB visit, hang around for the sessions. The NAB is sponsoring a number of digital tutorials this year, and I'll have an hour-long troubleshooting seminar for non-RF engineers on Thursday afternoon. Hope to see you there!
Submissions for this column are encouraged, and qualify for SBE recertification credit.