MGL Avionics User Forum

hi , getting frustrated and annoyed , i have in stalled a dicovery lit and rdac , power to both systems is good, rdac has a pulsating green light, both 9 pin plugs have resistors in them and voltage at efis end is showing 3 volts. problem is the efis is showing red x on all engine and radio displays . Does anyone have an idea what the issue is . thanks

Your RDAC should show a double flash every second - if it is a single flash it confirms what your EFIS is telling you - there is no data communication between the two. How did you wire your resistors and CAN bus and what are the resistor values ?

i have rwo resistors , one at each end in the 9 pin d sub the ar 12 kohms

i wired the across the 2 can hi lo wires at each end

Rocknrollrefugee wrote: ↑Mon Apr 22, 2024 10:29 am i have rwo resistors , one at each end in the 9 pin d sub the ar 12 kohms

They should be 120 ohms, not Kohms.

i will check i may have typo error but thanks

For the relatively short runs used in our aircraft I find just a single 100 ohm (or 120 ohm) resistor placed anywhere on the CAN bus is all that is needed. Make sure you wired that resistor between the two CAN bus wires and also make sure you did not swap the lines (CANH -> CANH and CANL -> CANL).
On some systems CANH is labeled CAN+ or even CANP and CANL is CAN- or CANM but that's all the same.

on further investigation can hi and lo are wired correctly, how ever the resistors that were given to me are 56 k ohm not 120 ,so i am oredering new ones as we speak , also does the rdan have to be earthed at the 9 pin as well as the earh slot on the right hand side of the rdac .thanks

Please refer to the RDAC installation manual with respect to grounding as this is very important.

In a nutshell - the RDAC must get its power supply ground directly from the engine block and nowhere else as otherwise it cannot measure any sensor that uses the engine block as ground accurately.
The ground terminals on the RDAC are normally not used but are available as convenient points to ground otherwise isolated sensors (so rather than grounding these to some unknown ground potential you ground them to the RDAC).