Thank you for the completions, Oilen! :aplauze:
PrinzEugen, first of all you must check the functionality of group BD651+R3+BC547 (power section), then the functionality of CD4093 (signal section) and so on, according to what you find during tests. I was going to tell you all these, but... step by step
I see 3hree steps to check the BD651+R3+BC547.
First you temporarily bypass completely BD651+R3 by connecting the BD651 directly to GND, to see if the full VDD voltage is fed to the rails.
Then you remove the bypass, disconnect R2 from pin11 and temporarily connect R2 directly to pin14, which is the V+ voltage of CD4093. This should completely open the darlington BD651, and the locomotive should run at full speed with the lights brightly lit. If the locomotive doesn't behave like this, then there is something wrong with R2 or BD651 or R3 or BC547.
Then you check the overload protection. Remove any train from the rails, set the multimeter as a 10-20A unfused (yes, you saw right) and touch the rails with the testers. This will be seen by the device as a shortcircuit, which will raise the voltage drop across R3 up to 0.68V, BC547 will open and pull down the BD651 base to GND, BD651 will close and won't let through a current greater than 1A, and this is what you will read on the ampermeter display. It is a little rough :fluierat:, but this is how the overload protection works. Or you can try to place across the rails a 1 - 10ohm power resistor in series with the 10-20A unfused ampermeter, to make it softer for the device.