Dale Lamm is with WHBC(AM) in Canton, Ohio. Our recent column “When Components Fail, Use Your Ingenuity” reminded him of one of the first hacks he had to do several years ago, after taking his current engineering position, when he had to repair a failed FM exciter power amplifier board.
C-44, a 1.0 μF surface mount capacitor on the PA board, shorted. The adjacent 15 amp SMT fuse also blew but not before the board was scorched, as seen in Fig. 1.
He removed all traces of the failed components and cleaned the board. Dale found a 0.22 μF Orange Drop capacitor, which he tacked on the board to replace the failed 1.0 μF. An inline fuse holder with a 15 amp automotive fuse was installed in the wiring harness feeding the PA board. This replaced the destroyed surface mount fuse.
Dale noted in his logbook, “Operations back to normal on 12/28-inch.” The exciter manufacturer quoted a new board at $1,815, a replacement board with trade-in of the old board was $464. Dale’s cost to repair was under $5.
As it turned out, this was not the last failure for this exciter. After two failures in the associated switching power supply board, Dale bit the bullet and traded in the board for a factory-rebuilt version. The replacement board has lasted since November 2013 without incident.
Responding to a photo of the distended ends of defective capacitors, engineer Duke Evans writes that he has repaired many a circuit board trace with bare wire.
Duke adds that some older electrolytics do not have the top crease in the aluminum, and when they explode, they explode downward through the rubber base. This then blows a hole in the circuit board! Not fun.
On one board Duke was able to fill the hole with E-6000 epoxy from Tap Plastics, not to mention lots of wiring. But his ingenuity saved the day.
Engineer Brad Johnson dropped a note saying our tip on the “automatic bypass for UPS AC power” was very useful. Glad to help, Brad!
If you have a mod or adaptation to improve your facility, share it with other engineers in the pages of Workbench.
I hear often that “Everyone knows that trick!” Not only is this not true, but best practices and fundamentals are becoming even more important given the number of younger IT folks involved in engineering who don’t have years of troubleshooting and transmitter experience.
Email your submissions, along with high-resolution photos to email@example.com. Published submissions qualify for SBE recertification credit.
Audio over IP brings a lot of features to the studio. One of the best, in my opinion, is the automatic mix-minuses that can be programmed for each channel. This foolproof feature eliminates the echo, feedback and general confusion caused by a phone hybrid feeding its audio onto itself when the wrong selector button is depressed.
Engineers still working with analog consoles have to depend on console labels to ensure the “right” bus pushbuttons are selected on the hybrid fader. Bill Frahm of Cumulus in Boise, Idaho, came up with a neat solution on his analog Arrakis consoles to prevent mix-minus foul-ups.
As you can see in Fig. 3, the UTIL (utility) bus is used for the mix-minus bus. The mix-minus is the mix of all the other faders on the console, minus the telephone hybrid audio.
To achieve this, the UTIL pushbutton on the “A PHONE” fader pictured in Fig. 3 cannot be depressed. Bill removed the module and inserted a plastic tie wrap around the UTIL pushbutton switch section, preventing it from latching on that channel. The mod is seen in Fig. 4, with the Philips screwdriver pointing to it.
Most mix-minus foul-ups occur when the operator inadvertently depresses the wrong button. With Bill’s mod, operators can depress the UTIL button for that fader but it will not latch. What’s nice about this modification is the module can be restored quickly to normal operation by removing the tie wrap; but in its present form, there’s no way the operator can select that bus accidentally.
Workbench is your column. Share your ideas with fellow engineers and qualify for SBE recertification credit while you’re at it. Send tips and high-resolution photos to firstname.lastname@example.org. Fax to (603) 472-4944.
John Bisset has spent 48 years in the broadcasting industry and is still learning. He handles western U.S. radio sales for the Telos Alliance.