i think the bad reading on IC3 PIN3 was operator error, after this the fan still did not work, and i mean i went back over all the pins and all the other readings were the sameHaving +15 volts on IC3 pin 3 indicates that either the base emitter junction of Q16 or it's emitter is not connected to zero volts. This will mean that over temperature will not be detected on the left hand channel. (You had a similar problem with the emitter connection of Q42 at around post #396.)
What was causing the loss of -15 volts on pin 4 of IC3 ? When you say "all other readings are correct" do you mean that the fan now works when shorting the base to emitter on either Q16 or Q42 ? ( When you are shorting the base to emitter of Q16 you may also be making contact between the emitter on the 0 volt track.)
Les.