On Wed, 15 Jan 2003 22:33:17 -0600, you wrote: Fortunately that is not the case. All 64 X, 64 Y, sense and inhibit lines have the correct resistance. I found fairly quickly that B MEM ENABLE was leaving its source but not getting to the core amps. I couldn't find the presumably broken wire on the backplane so I ran a jumper but still no function. (It's normally high all the time, so a disconnected TTL input is usually 1). this is somewhat depressing that the backplane may have reached end-of-life, if bad wirewraps are starting to show up. It is over thirty years old... Now READ and WRITE are pulsing to the selectors. Unfortunately I don't have a current probe to check out the R/W currents and waveforms. Guess I could put a .1 ohm resistor in the line which would give a 32 mv signal on the 320 ma pulse. -Charles