Handy Board FAQ Answers: “wontturnoff”
When I turn the Handy Board off, the BATT and PWR LEDs stay on!
This symptom occurs when current from the memory power supply (which is always on, to preserve the contents of the RAM) bleeds into the CPU power circuit.
Typically, this indicates a failed chip in the memory circuit (possibly the RAM itself), or, a board short between the memory power supply and a chip in CPU circuit (i.e., just about any other chip on the board).
To debug this situation, remove the LCD screen and turn the Handy Board off. Presumably the BATT and PWR LEDs are still on. Begin by removing U2, the 62256 RAM chip. Do the LEDs go out? If so, the RAM chip has probably failed; try another one.
If not, remove U7, the 74HC132 chip. This chip is part of the memory circuit and is also always powered. If the LEDs go out, this chip is probably faulty; replace it.
If both U2 and U7 are removed and the problem persists, it is probably a board short. One at a time, remove additional chips to see if you can make the problem go away. If when a particular chip is removed, the LEDs turn off, then there is probably some shorting path from the U2/U7 chips to the chip just removed. Check the board for stray leads or other defects.
(Last updated 2000-09-27)