troubleshooting processors and selftests

Discussion in 'General Electronics Chat' started by project robot, Apr 8, 2009.

  1. project robot

    Thread Starter New Member

    Mar 13, 2008
    I am troubleshooting a circuit board with a RTC (real time clock). The RTC has a battery on board to keep time. Normally the board powers up with a LCD displaying the model and then runs a self test of its other circuits. Some times after I program the flash (in circuit), the board powers up with no display. The fix for this was removing the battery from the RTC and waiting a minute. This seems to randomly fix the problem. Some boards work after the RTC has been replaced. I looked at the data sheet for the RTC and was interested in the SCLK pin.

    SCLK (Serial Clock Input) – SCLK is used to synchronize data movement on the serial interface for
    either the SPI or 3-wire interface.

    I set up a power supply with a current limit, and forced the SCLK pin high for a second. Thinking the Processor is not synced right with the RTC. It Worked, but I could not get the timing right, some boards I tried repeatedly with different time durations. Finally I just left the SCLK pin pulled high at power up until the board generated a selftest error. Then cycled the power on the board and it started fine.

    My question is, can putting 3 volts to the RTC chip damage it, or damage the processor?
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    Can you post a copy of your schematic so that we may see the overall circuit arrangement you are dealling with?

  3. project robot

    Thread Starter New Member

    Mar 13, 2008
    No, I can't not post a schematic Due to my companies policies about there customers designs and copy rights. Basicaly I want to know it is bad to maipulate the digital I/Os of ICs in circuit. I know that ICT machines do this to test certain products and components.

    Example: A processor wich has pull up and pull down resistors to enable a boot mode can be forced into another mode. So that ICT may do a boundary scan of the processor.

    I was thinking about writing a pic program to automaticaly pull the SCLK pin high, when a board fails to show a display.
    Last edited: Apr 10, 2009