MGL Avionics User Forum

My Challenger lite eifis isn't displaying the EGT's and CHT's properly when both RDACs are online.

To sort it out a bit, I tried powering up with the ULP RDAC not connected, the RDAC XG gives perfect thermocouple readings and the tach, oil temp and press are X'd out. Conversely, with the RDAC XG disconnected, the engine data is perfect but the thermocouple readings stay active with odd numbers like -147.
With both RDACs on line, the engine data is fine but the thermocouple info is all 32(F) with TC1 sometimes going off on it's own.

I've set the thermocouple sections of the screen and RDAC XG to RDAC2. All system setup menu items are set to custom screens.

I do wonder if the RDAC1 and RDAC2 TC channel scan setup's are correct. RDAC2 has the first 4 set to EGT and 5-8 set for CHTK but what about the RDAC1 settings? Currently, I have them all set on TC UNI 1 because they don't appear to be in the scan chain if I do that but I don't know if that's correct.
Any assist is much more than appreciated.

You would use scan chain 1 EGT and scan chain 1 cht for all of your RDAC TC channels.

EGT and CHT maintain independent scan chains. Scan chains are only relevant for numeric readouts that scan through the channels. This was the EFIS knows which channels belong together and they can cross RDACS.

TC Uni channels are "universal" channels that are neither EGT or CHT but could be used for other purposes.

Make sure both RDACs are correctly identified as RDAC 1 and RDAC 2 - if both RDACs are set to be RDAC 1 for example you will have both RDACs feeding in their measurements to a single display item (for example EGT channel 1).

Simple solution presented by Adam O'Connor was to toggle DIP switch 6 of the RDAC CAN to "on". Works perfectly now!