I have the same problem, crystal is tested and it is good, i hook up 32768 squarewave generator to pin 1 of DS1307 and it works but does not want to work from crystal only. I change 2 RTC chips (one SMD and one DIL) and both have same results. The source and schematic work perfectly in proteus. On the breadboard RTC works only with external signal as i mentioned. Could it be a library problem - I2C or DS1307? DS1307 are both working normaly with another HEX but i don't have source of it ... The dilema is great

 

I have the same problem, crystal is tested and it is good, i hook up 32768 squarewave generator to pin 1 of DS1307 and it works but does not want to work from crystal only. I change 2 RTC chips (one SMD and one DIL) and both have same results. The source and schematic work perfectly in proteus. On the breadboard RTC works only with external signal as i mentioned. Could it be a library problem - I2C or DS1307? DS1307 are both working normaly with another HEX but i don't have source of it ... The dilema is great

A lot of us here have used that RTC. The only problem I had with one was that the crystal took awhile to start initially. It then worked as expected. You seem to have ruled that quirk out.

I am unclear as to what you mean in the underlined sentence. As I understand it, you have tried the very same DS1307 using different compiled code, and it worked perfectly. However, since you don't have the source code for that, you wrote your own code, which doesn't work. If that is the case, then the problem seems to be with your code. Can you post your code?