Hi, i tried build a 555 timer, run the simulation, the result: Circuit: gooduntitled Doing analysis at TEMP = 27.000000 and TNOM = 27.000000 Warning: singular matrix: check nodes volprobe1 and volprobe1 Note: Starting dynamic gmin stepping Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Warning: singular matrix: check nodes u1_3 and u1_3 Warning: Dynamic gmin stepping failed Note: Starting source stepping Warning: singular matrix: check nodes u1_3 and u1_3 Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful source step Warning: singular matrix: check nodes u1_3 and u1_3 Warning: singular matrix: check nodes u1_3 and u1_3 Warning: source stepping failed Transient solution failed - Last Node Voltages ------------------ Node Last Voltage Previous Iter ---- ------------ ------------- xr3_1 -1.53627e-37 0 d2_1 -1.02655e-37 0 xr3_3 -2.01284e-39 0 v1_1 0 0 u1_3 0 0 volprobe1 0 0 r2_1 -1.54646e-37 -5.59605e-38 gnd 0 0 d1_1 1.00627e-30 5.59605e-38 u1_5 0 0 led1#branch 0 0 v1#branch -2.01284e-42 0 doAnalyses: iteration limit reached tran simulation(s) aborted Error(parse.c--checkvalid): volprobe1: no such vector. ngspice-26 done