Hello, I agree with John J. McDonough. He wrote many things to check and you should add to the circuit. I would like to add one more thing, because I faced with it in the last month and that was very instructive case for me. I always used electrolytic capacitor on the power line, and a 100 to 220 nf ceramic capacitor near to the power pins of the PIC. I am using 16F690 for a long time without any problem, but I decided to move for a cheaper PIC and that was 16F1618 with the same packaging. Unfortunately I should realise that PIC reset itself randomly. My first impression was that cause by BOR setting, and I checked the documentation, which is offered 10 nF ceramic capacitor paralell with a 100 nF ceramic capacitor on the power pins to avoid any malfunction of the BOR circuit. So I tried it, and the problem disappeared. I read the documentation of 16F690 with surprise, because the smaller parallel capacitor is there also. I don't think that this cause the problem of this sine wave circuit. Rather the vacancy of capacitors on the crystal pins , the vacancy of the pull up resistor on the MCLR pin, and on the RB4/PGM pin. One addition for this problem that there is two versions of 16f628. One is with "A" letter and one is without it. It is the older one. I realised differencies between them. If you want to work you circuit under 3V you should check the documentation about it for 16F628A on page 136: http://ww1.microchip.com/downloads/en/DeviceDoc/40044G.pdf Regards, Zsolt 2015-06-27 14:35 GMT+02:00 P Nielsen : > > PIC 16F628A-20 Sine Generator - Erratic Behavior on Vero > > Please see the circuit diagram here at box.com: > https://app.box.com/s/my4upsstcu1tjlhkvi00cu4fvaprp01e > > The PIC is programmed to produce 5 selectable frequencies using wave > tables. The PWM output is filtered into a sine wave via a passive LP > network. It is powered from a good variable lab supply. > > The voltage reference disables a flashing LED when the battery is low. > > The problem is that after successfully building the prototype on a small > piece of Veroboard, I cannot get it to work anywhere else. In particular > on a larger Veroboard or a solderless proto board. I have tried > everything I can think off ... several times. The PWM output looks fine, > but as soon as I connect the filter cap to deck, the signal dies. This > does not happen on the original build which is exactly the same circuit. > > I have installed a 104 cap across the rails and shortened any unused > tracks to no avail. > > What is the recommended troubleshooting procedure for a situation like > this. > > Can anyone offer any suggestions? > > Paul Nielsen > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 ~~~~~~~~~~~~~~~~ http://galzsolt.zzl.org --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .