MFD12 SST issues

A few months back when first used the unit in water, I noticed SST was -7 deg C. (should be about +20 deg C).

Temp sensor is part of the transducer (airmar 41-231-1-02, which I think is a B260) Brown & white wires to pins 4 &7.
In the Airmar schematic its described as a thermistor, so I assume its a PT100 which should be 100 ohms at 0 deg C. Am I right? (could be a PT1000)
I havnt checked resistance yet but will soon when back at boat.

Anyway I found the calibration menu and added approx. 20 deg C to it which brought it up to a more realistic figure. Since then I lost the temp altogether, and the bar graph range overlayed on the sounder screen I noticed is now unusable at about 30 to 50 deg.

Cant find in the menu where to change the displayed range. Can find C or F units and cal offset but how do I fix the displayed range?

If you are talking about the temp graph scale, you can not set the range yourself. It sounds like your temp sensor in the transducer might be going bad. Refer to this existing post on how to test it.
viewtopic.php?f=7&t=585&p=2386&hilit=ohm+temp#p2386

Thanks Johnny, yes Im referring to the temp graph scale. its lower value is higher than the water temp, so cannot possibly display correct value. hopefully it will fix itself when connected to a good temp sensor?
Thanks for the link, ill check resistance in the next couple of days.

I checked the resistance, about 58K ohm. So the thermistor in the B260 is obviously bad.
The displayed temperature range is 29 to 45 deg C.
Pretty useless as water temp around here typically 10 to 25 deg C.
Could the high thermistor resistance be the cause of the weird range displayed on the MFD12?

If the temp sensor isn't good, then your temp displayed on the MFD wont be.
58K ohm isn't good. I would suggest a separate temp sensor be installed to bypass the defective unit.

I fixed it.

I had a thermistor made by " Temperature Controls"

http://www.temperature.com.au/

I spliced it into the B260 cable.

I installed it into the top of my Perko 2 inch sea water valve, using a 2" NPT to 1/2 " reducer and a Thermowell. No more holes in boat.

contact "TEMPERATURE CONTROLS', ask for phil and quote " ralphs fix for WIDGEON"

Ill put up photos when I work out how to do it.
been tryin to insert a photo for last 2 hours I give up.

:jump