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Problem with AMC6821EVM-PDK kit

Michael Braband
Prodigy 60 points
Other Parts Discussed in Thread: AMC6821

Rafael - 

I started having been having problems with the AMC6821EVM-PDK kit today.  I think I offset the fan connector when I was plugging it into J1.  I'm not sure which way I went.  It seems the fan isn't getting the PWM signal, even though it shows up & changes in the registers.  Also, the fan TACH isn't showing up or changing in the registers.  It seems like something on the board is damaged.  Any thoughts on where to look?

Also, note that  on power up, the AMC6821EVM has two red alarm leds set:  THERM and FAN.  Also, the LOCAL temp is pegged at 99C, but the remote temp is responding correctly.

 

 

  • 0
    TI__Expert 6925 points

    Hello Michael,

    I read your previous post and I’m really glad you got it working. I checked the user’s guide, and I did see that J5 in figures 8 and 9 is the same. It is definitely confusing. I will see what I can do to change that.

    On power up, all red LEDs should be off, so those LEDs you see means something is wrong. Have you tried resetting the board without the fan?

    Try checking that the power supplies are giving the right voltages.

    By the way, Could you tell me the voltage on R11? This is the output of THERM pin.

    The AMC6821’s PWM output is open drain, so it can be driven up to VDD, but if you can see the PWM signal, then it is working.

    Offsetting the connector in J1 might have applied GND to the 12V fan input or 12V to the fan GND pin. Since 4-wire fans are very sensitive to reverse polarity, I think the TACH output and/or PWM control of the fan may be damaged.

    Try another fan, or you could try checking the one you were using.
     
    Do the following without connecting the fan to the EVM board to check the fan. You will need a 12V supply, 5V supply, a 1k-10k resistor, a wire cutter, and an o-scope.

    Note: keep the ground of the two supplies connected together at all times.

    1.
    In order to check if the fan PWM input is working, cut the cables from the fan connector and connect the PWM control wire to GND, and then apply power to the fan. This should keep the fan from moving. Remove the PWM cable from ground and connect it to the 5V supply. This should allow the fan to run at full speed.

    2.
    To check the TACH output, connect the PWM to a 5V supply for the fan to work at full speed. Then, connect one end of the resistor to the 5V supply and the other end to the TACH output of the fan. With the o-scope, check the TACH output signal.

    Let me know how it goes.

    Regards,

  • 0 in reply to Rafael Ordonez
    Prodigy 60 points

    I just tested the two fans that I was using, and they both respond to PWM signals from a signal generator.  However, they do not put out TACH signals when I use the pullup to 12V.  Based on this, and the info below, it appears my EVM and fans were damaged when I mis-connected the connector.  I tested a new fan, and I can see it's TACH signal on the scope.

    ****************************

    I tried resetting the board without the fan, and it restarts the same every time - with the FAN & THERM alarm LEDs ON.

    I only have a 12VDC power supply connected to J7 on the EVM.  An there is 5VDC coming from the USB connection to the MODEVM.

    The voltage on R11 is 2.744V.

    I have my scope probe on J5 Pin 11.  When I power cycle the EVM, I do not see any PWM signal at startup or when I load the various setting files.

    However, I can see the PWM *value* change in Register 0x08 in the Eval Tool.  The following chart shows the PWM *value* being recalculated based on the remote temperature, but there is no actual PWM signal at J5 Pin11.

     

     

     

  • 0 in reply to Michael Braband
    TI__Expert 6925 points

    Hello Michael,

    R11 should be pulling the THERM pin to 3.3V or 5V, so something is wrong with the board. THERM pin is an interrupt input that disables PWM control. If the voltage is not pull up properly, then the PWM is disabled, and I believe this is the main issue.

    First, check if the board is receiving the right voltages from J6 without connecting the 12V supply.

    J6 pin 10 should be 5V
    J6 pin 9 should be 3.3V (this is regulated from the USB connection by the MODEVM)
    J6 pin 3 should be 5V

    Second, if the power is fine, try changing some jumpers. Make sure the power is down when doing any jumper changes, and always disconnect the 12V supply before powering down the board.

    To have only the 5V supply running the AMC6821 change these two jumpers:

    1) With W7 in the default position, R11 pulls the THERM pin to 3.3V. So, change W7 so that R11 pulls the voltage to 5V.

    2) W6 controls the power for the AMC6821. By default, it uses the 5V, set W6 so that the 5V supply is used to power up the AMC6821.

    J4 pins 11 and 12 connect THERM to the MODEVM, so remove it on order to isolate the THERM pin from the MODEVM. If removing this jumper is what fixes the problem, then the MODEVM is the one damaged.

    Let me know if this helps.

    Regards,

  • 0 in reply to Rafael Ordonez
    TI__Expert 6925 points

    I made a little mistake in my previous post:

    By default, W6 powers the AMC6821 to 5V, so if you already have it with the default position, don’t change it.