Quoting "Leslie, Shawn J" : > I am using a PIC18LF4320I/ML. I am using Timer 1 and the oscillator = > as an RTC. I am driving the oscillator with a Epson FC-135 series = > 32.768KHz 12.5pF crystal good to 85C. I am hanging 27pF caps off the = > crystal. After 2 years of successful builds we are suddenly having = > this circuit fail at high temp. The oscillator fails at 60-70C and a = > few even do not work at room temperature. I am having 40% fallout = > at temp. If you lower the temperature to <40C it starts to work = > while power is applied. The problem is made more difficult since = > the units are potted. We cannot get at the components to = > troubleshoot. We are trying to test unpotted units over = > temperature. In the meantime I have tried to find a threshold of = > failure on a working unpotted unit by increasing and decreasing the = > 27pF caps - amazingly the circuit works at room temperature with = > 47pF caps on the high end to 6pF on the low end. With 6pF I can = > make it fail if I raise the temperature to 70C, but as it cools it = > begins to wor! > k. I have wrote Epson for crystal ideas and sent them my layout - = > any ideas from you guys? What have you all used? Maybe someone has a = > successful crystal oscillator design I could use. I suspect that the system problem may be more related to the PIC in this case than the crystal. There are a couple of (IMO) very serious = errata that apply to that micro for temperatures above 70=B0C. = Experience suggests that finding one or two cockroaches may be a good = indication that there are more of them about. Suggest you see if you can get any info out of Microchip. In the meantime, try another type of PIC that has the Timer1 = oscillator, but does not have the errata items I mentioned, and see if = you can prove (or at least get an indication) it's tied to this = silicon. 22pF should be a bit closer to optimum, but it's doubtful = (confirmed by your testing) that cap values would result in much = change other than a slight error in frequency. Best regards, Spehro Pefhany -- = "it's the network..." "The Journey is the reward" s...@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist