I installed the new rcmc board friday evening and tested again with the 2 aux smoke units disconnected. As expected all other functions worked correctly.
I plugged in only the whistle smoke unit to the sfc board and powered up....the chip on the sfc board began heating. So I removed this smoke unit from the engine again and went over every wire with a fine tooth comb. Could not find anything amiss visually. Went ahead and ohmed out each pin again to each other and compared the readings to what I got when doing the same on the main smoke units.
Ah ha....finally found something different. On the main units between the HTR pin and COM pin I had open line or a high reading of like 2 megaohms which is basically no connection. However, on BOTH of the aux smoke units I was getting a reading of around 29 Ohms between these 2 pins! I thought ok...maybe we're finally on to something here since I shouldn't be getting this reading between these 2 pins if I don't on the main ones right?
I confirmed it multiple times....Definitely 29 Ohms between HTR and COM pins on both aux smoke units, but not on the 2 main units. All other pins seemed to give similar readings on all 4 smoke units as noted below:
Between raw and htr = 8 Ohms
Between fan and com = 11 Ohms
Between sens and com = 7.5 k Ohms. when connected to a board...when. disconnected 53 to 56 k Ohms.
Between sens and htr = open line
Between raw and any other pin = open. line.
So there definitely seemed to be an anomaly here...htr and com giving me 29 Ohms on the 2 aux units but not the stack units. I went ahead and pulled both of those smoke units apart again...but still didn't really find anything to explain this behavior. I tried moving the thermistor a bit to make sure it wasn't maybe touching the element when assembled and I cleaned the top of the smoke unit pcb with alcohol thinking maybe there was a film of smoke fluid causing a short somehow. Reassembled them...and now I no longer read 29 Ohms between HTR and COM on either of them. All four smoke units now read the same.
But...I don't really know what I did to change or fix anything since I didn't see the thermistor touching the element unless it was when it was assembled... or the fluid was in fact causing a problem.
Went ahead and tried them again on the sfc board. The chip still heats up after about 2 minutes...and neither whistle or blowdown smoke work. The whistle smoke appears to be heating up now but the fan did not spin when blowing the whistle. Blowdown appeared to be totally dead still as I didn't feel any warmth nor did the fan activate when activating the feature from the cab2. Plus we still are getting a hot chip on the sfc board after some time. It's not instant now like before but it's getting hot enough that i feel if I left the power on much longer it might pop. Note that it doesn't warm at all with the smoke units disconnected no matter how long the engine is powered up.
So I guess my questions now are this:
What is the normal reading for the connection between HTR and COM? I'm assuming open or high megohms...but since it still isn't working I want to confirm normal before we try a 5th sfc. Defintiely not 29 Ohms though correct?
Why is the chip still heating up on the sfc if the smoke units are ok now? Damaged board from prior tests? Mis-programmed?
Any thoughts on what was causing there to be a connection on those pins initially and what I may have done to correct it? Is it corrected or is it likely to suddenly act up again without warning? Should we be replacing both of the aux smoke units?
Do you think we cooked the sfc again from all the prior testing and now we might be good to go with another new sfc? Or do you think this sfc is programmed wrong and thats why it's still not working?
This is one strange engine...its not gonna succumb to us without a fight until the very end I guess.