A friend gave me something to repair. The device is operating from just the strangest wall wart. The wart looks fairly standard, like any generic charger for a mobile. On the outside it says 6V 330mA. This one died and doesn't put out any voltage anymore. Inside the wall wart, it seems like the unmarked IC controlling the switching gave up. Must be a micro of some sort.
I tried to replace it with a generic cheapo that can switch the voltage between 3,5,6,9 and 12 V. Didn't work..
...until I accidentally set the new generic power adaptor to 9 V instead of six volt (because I'm dyslexic or something). I realized my mistake and quickly set it back to 6V. To my surprise the device started operating normally. Turns out this is reproducible. To make the device work, I have to feed it with 9V for a small time (no more than two seconds or it won't turn on) and than switch it back to 6V. I assume this is so one needs to buy the expensive power adaptor from the device's manufacturer? Do you know of something else that could cause this behaviour? Have you encountered something like that?
Also what is the best way to shoehorn a board that puts out 9V when first connected for about a second and then 6V while powered from 6V? I'd like to have a good solution for that from standard components I have lying around (maybe a 555). The device doesn't draw more than 10 mA in the 9V phase, and starts drawing its regular current of about 150 mA once in the 6V phase.
But mostly I'm curious as to why this device behaves so weirdly. As to the nature of the device, it's an expensive toy.