Editing PDP-11/70 Troubleshooting Guide (section)

== Quick checks from the service guide ==
=== Data path check ===
Deposit all ones and then all zeros in location 0 and examine them; deposit 070707 in location 0, load address 17000000 and examine. Reading 070707 through the Unibus map shows the data and address paths are good; repeat in reverse.<ref name="msg145" />

=== CPU voltage margins ===
All CPU and RH70 logic should run without errors with the +5 V regulators anywhere from 4.75 to 5.25 V. Set all the CPU (and used RH70) +5 V regulators to 4.75 V and run EQKC for half an hour, then DEC/X11 for half an hour; then repeat at 5.25 V. If errors appear, move the regulators back one at a time to find the module concerned.<ref name="msg145" />

=== Timing margins ===
With a jumper from F13J1 to E21T1, set R162 on the M8139 timing board for 250 ns at D13T2 and run EQKC, then 140 ns and run it again, then return to 150 ns and remove the jumper.<ref name="msgpm" />