Odd behavior, PS2/3V S2 switcher

Add a second power tap at the other end. Fastrack pins don't make great contact.

Check track voltage before and after.

Tachometer runaway. The motor body moves and rotates to match the track curve compared to the frame. When that happens, the wiring flexes and for some reason you are losing the tachometer feedback to the board. The board then thinking the motor is not turning- turns up the voltage to the motor trying to make it goes the speed commanded but the tachometer is not reporting. The train takes off top speed and hits the other curve flexing the wiring again and now the tachometer is reading- hence the sudden slowdown back to the commanded speed.

So check your optical tachometer placement and gap to the flywheel, but also the wires and solder joints for the tack board.

@Vernon Barry posted:

Tachometer runaway. The motor body moves and rotates to match the track curve compared to the frame. When that happens, the wiring flexes and for some reason you are losing the tachometer feedback to the board. The board then thinking the motor is not turning- turns up the voltage to the motor trying to make it goes the speed commanded but the tachometer is not reporting. The train takes off top speed and hits the other curve flexing the wiring again and now the tachometer is reading- hence the sudden slowdown back to the commanded speed.

So check your optical tachometer placement and gap to the flywheel, but also the wires and solder joints for the tack board.

🤣 It was the bright sunlight through the window messing with the tach sensor. I just stumbled upon that after inadvertently blocking the light.

Yep, that'll do it. That's why the tach motor is always buried in the back of the engine away from the cab.

As a temporary solution, removed interior tray and battery try, allows for larger AA battery pack.

Guess I'll see about a bcr2 on next order from somewhere.

It's good to have it running smoothly again, it was always one of my favorite switchers.

@Rod M. posted:

🤣 It was the bright sunlight through the window messing with the tach sensor. I just stumbled upon that after inadvertently blocking the light.

.......stumbling is a great scientific research tool

@Rod M. posted:

Guess I'll see about a bcr2 on next order from somewhere.

Make your own.  Here's how I do them, I just cut the leads off the old dead battery and use them to solder to the 1.5F 5.5V supercap.

Is that one cap, or two bundled together and how do you size up the shrink wrap for those?

I have to order everything as there's nothing local

Rod, Those supercaps are packaged that way. All you have to do is solder the snipped wiring harness onto the two leads.

This is what you'll need to order: https://www.digikey.com/en/pro...R22D155PRBB0/8028726

@Rod M. posted:

Is that one cap, or two bundled together and how do you size up the shrink wrap for those?

I have to order everything as there's nothing local

As stated, that's how a 5.5V model comes, the heatshrink is from the factory.  That's easy to tell as it has the actual capacitance and voltage rating printed on it.