S100 address buss troubleshooting

That should be easy enough to troubleshoot. Use a logic probe or your logic analyzer to monitor the A13 line while you remove the CPU and memory cards one at a time. You should quickly find which is causing the problem. If you pull all the cards and the bit is still stuck then it's time to troubleshoot the front panel. You can do the same for the stuck A7 bit. Then check before and after the address buffers on the defective cards. You'll probably find a defective buffer or a memory IC with a stuck bit. If the ICs are socketed it should be quick to troubleshoot. One thing to be aware of is if you have a non-inverting buffer on the line and the buffer's input is floating due to a poor connection then it will force the buffer's output high so check the buffers carefully. Some of the old ICs can be a real bitch to troubleshoot. I've seen some that had hairline cracks right where the lead enters the IC body. The lead would be driven high or low but the input to the IC was actually floating and that forced the output high or low. This is one of the big problems that I found with socketed ICs. The socket and IC lead are made of different materials and cause electrolysis. They would look ok but the IC leads frequently fell off the IC bodies if I tried to remove them from the socket. I seldom find this in military or high grade commercail equipment since they use high grade parts and pay attention to details like this (dissimilair material) but it's common in cheap commercail or hobby grade equipment. I worked on a RCA VIP a couple of years ago that was full of ICs like this. I've also seen the same promblem in several Heathkit 6800 trainers. Storage is humid conditions definitely aggravates the problem. Joe At 06:26 PM 6/4/05 -0400, you wrote: