PDP-11/40 success (sort of)!

After the better part of 2 weeks I've finally gotten one of my PDP-11/40's to execute some code. Both initially exhibited frustrating similar problems. Both were stuck in "reset". This was because the processor was seeing AC-LO and DC-LO asserted. While the symptom was the same, the cause was different. In one case the power supply was not deasserting the signals. In the other, something in the RK-11D was pulling the signals low. I've worked around both but fixed neither. Once that problem was solved on the "first" 11/40, I discovered that there was a stuck bit when trying to read or write memory. This was temporarily fixed by swapping the data-paths module. At this point I could read and write to memory. Memory could be read and written through the front panel, but execution would immediately trap to location 4 (6 showing on the front panel). This was a "bus error". I unfortunately spent a lot of time swapping memory around (this was not the problem). Replacing the data-paths module with another suitably jumpered one solved the problem and the 11/40 happily runs a little test program. However, at this point I'm hesitant to run it for very long since there is an acrid smell emitted while the system is powered on. I don't want to burn anything up until I track it down. The second 11/40 still traps to location 4. I've verified that the memory is good by swapping memory boards and backplane (I'm using MF11-UP memory) with the first 11/40. I checked the supplies and they seem a little low, but it got late tonight and I'll check and adjust them tomorrow to see if that fixes the problem. It's a bit hard to determine if any one card is at fault because the two 11/40 CPUs are configured very differently (which means there are almost 2 dozen jumpers between all the boards that need to be changed). Here's the 2 different CPU configurations: CPU #1 CPU #2 KD11-A KD11-A Basic CPU KE11-E KE11-E EIS KE11-F FIS KJ11-A Stack limit option KT11-D Memory management I have another set of CPU boards (but no extra FIS) that if the voltage checks don't solve the problem I'll try to see if that fixes it. If anyone has any other suggestions, I'd appreciate hearing from you. -- TTFN - Guy