Hi Mark, Thanks for your suggestions. The more feedback I get, the more encouraged I am that this is worthwhile pursuing. One of my contacts yeterday told me of a collegue with half a dozen faulty boards ... though I would suspect that out of the six, perhaps only one or two may need a new micro. Your comments on the 5.6 volts may be correct ... that is one of the reasons I was looking for details on the original micro to find out what it's specs were supposed to be. Thanks again, Roger From: "Mark Rages" On Thu, Aug 13, 2009 at 8:34 AM, Roger Weichert wrote: > And also the supply. From the data sheets I see that 5.6 volts is too > high. > > I may just be showing my ignorance ... but if this other microcontroller > has worked for 20 years with such a crude supply (5.6volt zener and a > cap), > is it possible that a 5 volt shunt regulator could be used .. (is there > such a thing?) ... to keep it safe. > You can add a SOT-23 LDO regulator to your adapter board. MCP1700 or something. 5.6->5.0 V is an easy spec to meet. Read the datasheet and add the capacitors it asks for. Note that the microcontroller that worked for 20 years is not working any more... so maybe 5.6V was a bit high for it. The PIC internal osc works fine, but if I was in your shoes I would probably re-use the crystal. I'm sure you're right about accuracy not being super-important, but I like to have RS-232 configuration / debugging in my designs, and a crystal makes a better baud rate generator over temperature than the internal oscillator. Regards, Mark markrages@gmail -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist