Service required for HP 9160A Optical Card Reader

[Jurgen Keller]

(01-06-2016 10:32 AM)jebem Wrote:  - Test for power supply short circuits again, but without plugin in the two PCBs, then one OCB, tehn the other PCB, to find out where is the short-circuit.

The short circuit is on PCB1, the one with the burnt inductors. That's the expected result I guess.

(01-06-2016 10:32 AM)jebem Wrote:  When the motor is energized, this lowish resistance value cause a large initial rush current, but this is normal and should not blow the fuse, as long as the motor can start rotating to let its impedance to rise fast to the normal value and let the current decrease rapidly.
(fuses can stand larger current than the specified value for a short time, specially if they are slow blow).

Now, if the motor can not rotating because it is mechanically blocked, its impedance will not rise and the current will remain high resulting in the issue that you describe (blown fuses and series resistors/inductors burnt).

That makes sense to me. However, I don't have the impression that the wheel is blocked, I can rotate it manually without much force.

Furthermore, I wouldn't expect that the wheel turns right from the beginning, only when a card is inserted. There is kind of a switch above the wheel which lifts the silver metal strip you can see in the middle of "Device Pic5". I think that's the mechanism to start the motor.

I've also verified that my replacement gummy ring lifts the metal strip a bit, maybe enough to start the motor right from the beginning. So I think the diameter of the replacement ring is definitely too big. I should have understood the mechanism better before inserting a replacement wheel. It's easy to be wise after the event.