dumper circuit

Use .ic together with uic.

It sims fine if I click the box to skip the initial condition solution. That's faster too. Delaying the power supplies breaks the tie too.

What I don't understand is how negative feedbacks work during the ic solution, but positive feedbacks don't.

Strongly non-linear ODEs and systems of ODEs are more likely to have singular solutions i.e. parts of the domain where the initial value problem fails to return a unique answer...I'm not an expert in how this translates to discretized/numerical solutions but I believe the same sort of thing applies, a system of finite difference equations describing a positive-feedback circuit is more likely to be strongly non-linear than one for negative feedback.

Sometimes an initial value problem is only troublesome at a single point like t = 0 and if you move off that point the problem is well-posed.

Version 4 SHEET 1 880 680 WIRE 272 -16 208 -16 WIRE 336 -16 272 -16 WIRE 336 0 336 -16 WIRE 336 96 336 80 WIRE 208 112 208 -16 WIRE 80 128 32 128 WIRE 176 128 80 128 WIRE 272 144 240 144 WIRE 288 144 272 144 WIRE 304 144 288 144 WIRE 176 160 128 160 WIRE 208 208 208 176 WIRE 128 240 128 160 WIRE 272 240 272 144 WIRE 272 240 128 240 WIRE 32 288 32 128 WIRE 208 288 32 288 WIRE 272 288 208 288 WIRE 32 320 32 288 WIRE 272 320 272 288 WIRE 32 432 32 400 WIRE 224 448 208 448 WIRE 272 448 272 400 WIRE 272 448 224 448 FLAG 208 208 0 FLAG 336 96 0 FLAG 32 432 0 FLAG 272 -16 +10 FLAG 224 448 +10 FLAG 80 128 N FLAG 208 288 P FLAG 288 144 U SYMBOL OpAmps\\UniversalOpAmp2 208 144 R0 WINDOW 0 -63 48 Left 2 SYMATTR InstName U1 SYMBOL voltage 336 -16 R0 SYMATTR InstName V1 SYMATTR Value 10 SYMBOL res 48 416 R180 WINDOW 0 -52 67 Left 2 WINDOW 3 -58 38 Left 2 SYMATTR InstName R2 SYMATTR Value 10K SYMBOL res 288 416 R180 WINDOW 0 -46 69 Left 2 WINDOW 3 -54 39 Left 2 SYMATTR InstName R4 SYMATTR Value 10K TEXT -176 304 Left 2 !.tran 1 TEXT -224 208 Left 2 ;Opamp Startup TEXT -224 248 Left 2 ;JL Mar 8 2025

Run that for 1 second and look at node U.

Repeat but run for 10 seconds.

Then run for 1000 seconds.

It's doing nothing unusual. An output of about 5V is a valid state. If you need the simulation to start in a different state use .nodeset v(U)=0. That's exactly what the directive is for.