Working on PDP 11/40, issues with DC LO and AC LO The front panel confirms a DC LO issue, CONS and RUN lights are off, BUS and PROC lights are on. The panel is unresponsive. With the cable removed from the h742a connector, P9 says DC LO and AC LO are 3.53v, which is lower than the expected +4.8v. This tells me there is a fault in the h742a. I hate to remove the 742a power control board but I finally have the machine in my basement so I can work on it for an extended period. Voltages of the other regulators are OK. I think it's conclusive that the h742a has a fault to be repaired. Next, I re-connected the cable to P9. The DC LO and AC LO wires lead to J18, which feeds DC LO and AC LO to the backplane on my system. Reading 1.72v. I get similar readings from the backplane pins themselves. When I remove the Status Module card (M7235) from the backplane the AC LO on J18 jumps up to 3.53v - i.e. AC LO jumps back to origination levels. Question - Is there is *also* a potential fault in the M7235 circuit related to AC LO, -OR- is it normal for the M7235 to detect and pull down AC LO further forcing the system to halt? I am working to understand the circuits from page 120 of the KD11-A Maint manual http://bitsavers.trailing-edge.com/pdf/dec/pdp11/1140/KD11-A_Maint.pdf My plan is to repair the h742a first and see how it goes, but I'd like a 2nd opinion if anyone has one, regarding the M7235....thanks! photos http://vintagecomputer.net/browse_thread_record.cfm?id=178&tid=8 Bill