Fluctuating EGT's

[fabjab]

Any ideas; I assist at a local avionics shop and we they have the following problem.

EFIS D100 DSAB linked to EMS D120 for about 6 months now. No problems with EGTS's. During current visit to the shop added a serial connection between the two as well as connected SL30 and Garmin 296 connection to EFIS.

With serial null modem in place EGT's (and only EGT's) fluctuate through about 150F in flight. I am not sure but the switch to disconnect serial port from SL30 connection might be wrong, so we might have SL30 and serial port connected in parallel ( I will check tomorrow)

Any ideas

Blue skies,

Carl.

 

[dynonsupport]

Re: Fluctuating EGT's

The first thing to do would be to pull apart the new serial connections to see if that's what's causing things to go haywire. If they do, start checking pinouts. A serial connection going to the wrong pin could produce some strange effects.

 

[fabjab]

Re: Fluctuating EGT's

The problem was the fact that the SL30 and the serial port of the EFIS was always connected. Installed a switch to isolate FLIGHT MODE - EFIS to SL30 or UPDATE MODE - EFIS to D9 serial port; and problem solved.

 

[dynonsupport]

Re: Fluctuating EGT's

Of all the weird things, given our schematic, this makes sense. If the EMS RS-232 transmit port is getting really messed with, it messes with other voltages inside the unit and can cause EGT and/or CHT problems.

It doesn't permanently hurt the unit, so no worries there.