We used a pair of matched 1N4148 diodes as the temperature sensors in the ID-1290, ID-1390, ID-1390A, and the ID-1390B Indoor/Outdoor digital thermometers.  These diodes were matched for Forward Voltage so the two temperature sensors could be balanced.  A silicon diode has a physical property of the Forward Voltage changing 1 MV per 10 degrees (C) and is fairly linear.  This Forward Voltage can be used to measure the ambient temperature and that is how these temperature sensors work.  Over time, the diodes can fail and the temperature sensors will no longer work.

We have been asked over and over again what the specification was for these diodes.  There is no actual specification, as long as each diode is fairly close to the rest in Forward Voltage. 

This kit provides 4 matched 1N4148 diodes for use in the temperature sensors.  To repair your existing sensors, you simply remove the existing diodes from temperature sensor cases using a small drill bit (by hand) from the wire side.  Once you have the aluminum tubes cleaned out, you can simply rewire the two diodes in series into the existing aluminum tubes.  The manual shows the diodes wired in series on the schematic.  In cases where the temperature sensors are completely missing, we have had good luck using an eyebrow pencil cover that is made of aluminum.  Once the diodes are in the aluminum tubes, simply seal the whole thing using silicon sealant that can be found at most any hardware store.

Make sure you use a non-acid curing 'silicon seal'.  It has been brought to my attention that some lower priced 'silicon seals' (generic term) use an acid based curing agent.  These can be corrosive to electronic circuits.  To test:  put a small amount on a piece of paper and let it cure.  If it smells like vinegar, then it is an acid based curing agent.  Maybe you can also check with the manufacturer and see if that specific 'silicon seal' is acid based or not.  

This was a new one for me...