I received a pdf from one of the others on the list. The pdf shows that the 861 is not exactly like the 7420, in that the unused pins of the 7420 are for gate expansion on the 861. The circuit that uses the part, I think is failing, doesn't use these pins. The biggest potential problem I see is that the original designer used two outputs tied together. This means that the other output has to pull it down as well. I tried a 74LS20 and it didn't work but I think it is just that the 74LS20's have a strong pull-up. I'll try to locate a 7420 and give it a try. I've also found a part supplier that

stocks old DTL and even RTL parts. I haven't contacted them yet but if the 7420 doesn't work I'll give them a try. They have these in the Motorola part numbers. For others looking for old parts, they are: http://lansdale.com/~lansdale/index.html I'm sure these will be expensive but then what the heck. Thanks for the reply Dwight