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A/D and D/A cal failure, HP54501A scope

Discussion in 'Troubleshooting and Repair' started by rpiengineer, Jul 25, 2012.

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  1. rpiengineer

    rpiengineer

    2
    0
    Jul 24, 2012
    The problem started with the infamous CAL RAM CHECKSUM ERROR. I replaced the NVRAM chip and performed a key-down power start. The self test said the A/D and D/A cal failed. I then performed a self calibration on all four channels. Here are the results:

    Status Function Diagnostics

    Failed A/D Cal Chan 1 0000 0000 0000 0100
    Failed A/D Cal Chan 4 0000 0000 1100 0100
    Failed Gain Cal Chan 1 0000 0000 0000 0010
    Failed Gain Cal Chan 2 0000 0000 0000 0010
    Failed Gain Cal Chan 3 0000 0000 0000 0010
    Failed Gain Cal Chan 4 0000 0000 0000 0010
    Failed Offset Cal Chan 1 0000 1000 0000 0000
    Failed Offset Cal Chan 2 0000 1000 0000 0000
    Failed Offset Cal Chan 3 0000 1000 0000 0000
    Failed Offset Cal Chan 4 0000 1000 0000 0000
    Failed Trigger Cal Chan 4 0001 0000 0000 0000

    I do not know how to proceed from here. Are there separate chips for the A/D and D/A functions? If yes, where are they located on the mother board? I have a component layout of the mother board. Any help is greatly appreciated.
     
  2. shrtrnd

    shrtrnd

    3,803
    507
    Jan 15, 2010
    The 54501A manual is notoriously unhelpful, as far as HP manuals is concerned.
    Do you have a manual?
    Page 4-7 (Section 4-13) DAC Refernce Adjustment.
    If you don't have a manual, here's the basics:
    (You need an ACCURATE, DVM)
    Invoke 'Service Menu' by pressing front-panel "UTIL' key, then select 'Service Menu'
    Select 'Cal Select 2" with softkey
    Set DAC Output to 'High Adjust'
    Connect DVM to rear panel DC Calibrator Output.
    Adjust System Board Assy R723 for DVM indication of 5.000V (Refer to figure 4-4 if tyou
    have the manual).
    Set Cal Select to 'Low View"
    Measure V1 to four decimal places ( 0.xxxx volts)
    Set DAC output to 'High Adjust'.
    Adjust Assy R723 for DVM indication of 5.000V PLUS V1, that you read (above)
    Exit Menu softkey and the O'scope will return to the Utility Menu.

    The manual says if that doesn't do it, a module has failed and says it needs factory repair.
     
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