There are still plenty of analog strobe light systems installed, some intermittent and others completely inoperative. While limited troubleshooting effort might be in order to determine if a fix is simple, we think you should use caution with old systems because the money might be better spent on either a drop-in replacement (we covered them in a roundup in the March 2024 Aviation Consumer) or a new install. For that, we think the uAvionix skySensor is a smart choice, and it’s one that doesn’t get enough consideration because many shops might not suggest it.
First, here’s a brief overview of what can go wrong with old systems with external power supplies.
Use it or lose it
Like many systems on the aircraft, long periods of inactivity are detrimental to strobe system health. A strobe power supply that has been left “off” for long periods—weeks or months—is subject to eventual failure because the electrolytic capacitors used in the device will lose polarity formation. When a voltage is applied across the device, electrical energy is stored in the polarized dielectric. Failure can occur any time the capacitor’s hermetic seal is broken, allowing dielectric to leak out. But failure also occurs when there is breakdown of the surface coating of the foil layers, which happens slowly and progressively during inactive periods.
During active use, the applied voltage usually causes enough redepositing (replating) to fully restore the foil—if the surface breakdown was not excessive.
After a long period of inactivity, however, the foil surface may not reform when a voltage is applied. Instead, the voltage is dissipated as heat and the capacitor dies. If the plane sits for a month or more, it might pay to at least exercise the strobe power supply for a few minutes every week. This obviously isn’t always practical, but it also means you should use caution when powering the system up for the first time because that’s when failures occur. Operate the power supply on a reduced voltage (75 percent of normal) for 10 to 20 minutes (even a weak battery in a non-running airplane will help prevent overheating of the capacitors as they reform).
What about merely turning on the strobes at full system voltage? There is an excellent chance of the capacitors overheating and self-destructing as you taxi out for takeoff with 14.4 or more volts hitting the capacitors from a running engine instead of 12.3 volts with a shut-down engine at low battery voltage. A more professional way is using an appropriately sized adjustable 12- or 24-volt power supply, of course.
Keep it simple
The first step in troubleshooting any strobe system is to determine whether the trouble is in the flash tube or the power supply. This is easy, if you can substitute a known good flash tube for the one in question. If a spare flash tube isn’t available, just turn on the strobe power supply and put your ear next to it. A properly working power supply emits an audible tone. Actually, it’s a high-pitched whine.
Most common strobe systems are protected against shorts or opens on the output and will, in essence, shut themselves off when subjected to a flash tube that won’t flash. But you—the troubleshooter—are not so protected; don’t let yourself get shocked. Strobes are high-voltage devices. Always let the power supply bleed down for five minutes before handling. Also, reversing polarity of the input power, even for an instant, will permanently damage the power supply. Such damage will not always be immediately apparent. Sometimes failure occurs later. Use care when detaching and reattaching wires to connector pins. It’s easy to assume that in the latest versions of these power supplies there would be reverse polarity protection—there generally is not.
Got a multimeter? A good place to start if you’ve ruled out the flash tube as the culprit is to determine whether there is appropriate input voltage (14 or 28 volts DC, as applicable) at the power supply. Next, check the power supply operationally by disconnecting the output cables and connecting an operable strobe head (or bench check unit) directly to the power supply outlet. Upon applying voltage to the power supply input, if the output is normal, look for problems in the interconnect cables. In aging aircraft left outdoors, it’s not uncommon to find corrosion at the connectors. And since many power supplies live in the tail section, moisture is certainly the enemy.
Continuity should be checked for each interconnect cable. (Check for continuity from pin one to pin one, or red connection to red connection, white to white, etc.) Check for shorts between white and red, red and black and black and white. Worth mentioning is that belly strobes need drain holes. Be sure they are installed and clear. Check for shorts from any non-black wires to aircraft ground. When connections for red and black, or white and black, have been reversed, the system will appear to operate normally. Flash tubes will fail prematurely, however.
You may begin to notice that a tube flashes normally with the engine running but stops firing when the engine is shut down and the system is running only on battery power. When a tube begins acting strange in this manner, it should be replaced.
If the wiring checks good and the appropriate voltage is getting to the power supply but the system won’t operate, it’s time to contact the manufacturer. Some have flat-rate repairs and some shops will swap out the power supply if it’s the problem.
Inexpensive solution
There are plenty of modern LED strobe systems to replace these aging ones, but one of our top-pick budget solutions comes from uAvionix. The company had great success with its skyBeacon ADS-B Out wingtip device that also has built-in lighting, and the companion (or standalone) product is the skySensor, which has integral LED strobes, an ADS-B In receiver and a green LED position lamp. At $795, it’s almost cheaper than a shop invoice for troubleshooting a vintage strobe system.
The fin-style skySensor matches the skyBeacon’s footprint and form factor and fits the teardrop-shaped three-hole-mount Grimes nav light. It has TSO-C30C approval for Type II (forward, green) position light and TSO-C96b approval for Class II anti-collision/strobe light functions. The ADS-B portion doesn’t have a TSO (nor is it required) because the weather and traffic data it receives is considered supplementary. uAvionix has TSO’d wingtip mounting adapters for installations where the skySensor isn’t a drop-in fit.
As a deal sweetener, the skySensor has a dual-band (978 and 1090 MHz) ADS-B receiver for weather and traffic, and the GPS feeds position data to cockpit tablets. The skySensor can send traffic data (not weather) to uAvionix’s AV-30 electronic flight display when equipped with the AV-Link WiFi dongle—now approved for certified aircraft.
Like the skyBeacon (and tail-mounted tailBeacon), the skySensor has a stone-simple three-wire (red, black and yellow) interface. The red wire connects to the existing position light’s switched power source and the black wire connects to airframe ground. If replacing a position light that has an integrated anti-collision strobe, the yellow wire connects with the existing anti-collision light’s switched power (this is aircraft power and not to a high-voltage strobe power supply).
Last, we like that the skySensor syncs up with a companion sky/tail Beacon’s strobe pulses (once per second) using GPS clock time.
This article originally appeared in Aviation Consumer Magazine.
