garyvanremortel(at)gmail.
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 Posted: Sun Jan 19, 2025 8:00 pm Post subject: KLX-135A and other issues |
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Many RV builders in the ‘90s installed a Bendix/King KLX 135A Nav/Comm as part of their avionics suites, right up until everything changed and sophisticated Glass Panel Displays from Dynon, Garmin and the like started to become available. I’d like to get just a few more years out of my 6-pack steam gauges, original VM1000 and conventional radio stack setup before I fully upgrade my panel. I have ADS-B in/out and use a Samsung Galaxy S9FE tablet running Avare for navigation these days, with my smartphone and KLX 135A moving map as backup.
I’ve had a few issues with the KLX 135A that many may soon experience. My unit, originally installed new in 1997, now has ~1100 operational hours. I have a copy of the Maintenance Manual to reference for replacement parts, however Honeywell Bendix/King has been somewhat less than accommodating of end users in this regard, instead allowing only shops like South Eastern Aerospace to buy parts and do their repair work. Don’t get me wrong, SEA is a great shop, but boxing up and sending my unit off to FL for 6wks is not always a good option. Since retiring, I no longer have access to test equipment necessary for proper troubleshooting, but I am a USAF trained technician, comfortable with SMD defense electronics repair. So when I see a simple circuit with a simple problem, I assume I can fix it straightaway, if I can get the part(s).
The KLX 135A was a solid Nav/Comm at the time, but like all electronics, some components are inherently life-limited. Tadiran TL-5135 battery on digital board requires periodic replacement, Aluminum electrolytic filter capacitors on power supply and audio boards dry out, LCD display on main board bleeds out and reflector photo interrupters on frequency tuning dials get weak. Heat that the unit sees when parked on the ramp non-operating may also contribute significantly to limited life.
My internal battery has been replaced twice, once by LAC in San Jose, CA and more recently by SEA, but it is a relatively simple DIY job. LAC replaced the power supply and audio capacitors after having to go NORDO into KLVK one day, and more recently SEA replaced the LCD. When tuning of the decimal digits in the radio section began to get sluggish and didn’t always increment/decrement properly during rotation, I examined the unit and reviewed the simple circuit. My EE buddy told me the IR LEDs in the photo interrupters were likely getting weak due to age. After buying the last B/K 007-08094-0000 parts I could find in the states and replacing them, the unit now operates 5x5. The unit should last another 5 years.
-GV
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