BALCHECK MAY NORMALLY POWER ON WITH A BLANK (BLACK) SCREEN


When MCM Design was developing the original SetScreen, time was spent
experimenting to see how the custom data chip initialized screen parameters
immediately at power on. The results of the experiments were documented in the
original SetScreen doc and are now included in SetScreen3's doc. It was
determined that normally, during initial power on, the custom data chip will
attempt to initialize with a blank TV display. At this time it is not clear if
this observation only applies to the latest 1978 ROM version motherboard. MCM
Design indicated that it is up to the software to instruct the custom data chip
to set up (output) the desired screen display parameters.

Why is it, that sometimes when the motherboard is initially powered on, the TV
display initializes with scrambled graphics using menu colors, but no execution
of the menu routine occurs? Is this a mystery? Recently, while MCM Design was
testing its BalcheckHR board, an unexpected initialization was observed. For an
unknown reason, when a particular working motherboard, having a 1977 version ROM,
and the standard Balcheck tests were powered on simultaneously, the TV display
would initialize with 2 random colors and scrambled graphics. Apparently, the
custom data chip, under certain conditions, will initialize at power on with
some visible screen parameters.


The Balcheck screen parameters, including the colors, are NOT initialized until
the very end of the first pass of Balcheck tests, with one exception. The
vertical blank line is set (lowered) to 198 (C6 hex) right after the dual
display is initialized to - - (dash dash). Audio outputs will occur at the end
of each pass of testing.


The following scenarios describe visual TV screen outcomes, when an attempt to
initialize Balcheck is made. Descriptions 1 thru 3 apply to Balcheck being run
on a working motherboard. Decription 4 applies to a failed motherboard.

1. A WORKING motherboard is powered on BEFORE Balcheck is powered on.

   The menu routine sets the screen parameters. Balcheck will not change the
   screen parameters until the end of the first pass of Balcheck tests.


2. A WORKING motherboard is powered on AFTER Balcheck is powered on.

   Watch the dual display initialization, NOT the TV screen, after powering on
   the motherboard.

   A jump to the Balcheck tests at memory address 2000H will not be executed
   until the motherboard is powered on. Execution of the Balcheck tests may
   occur without pressing the system reset button. The screen display will
   likely remain blank (black) until the end of the first pass of the Balcheck
   test.


3. A WORKING motherboard and Balcheck are powered on simultaneously using a
   power strip.

   Watch the dual display initialization, NOT the TV screen, after powering on
   with a power strip.

   The TV display will likely power on with a blank screen, but may power on
   with 2 random colors. The initialization of Balcheck will likely occur
   without pressing the system reset button. Balcheck will not change the
   screen parameters until the end of the first pass of the Balcheck tests.


   MCM Design's motherboard #5 utilizes the old technology capacitors C6 and C1
   and the single 8KB ROM chip, the 1977 version. This motherboard and Balcheck
   power on simultaneously with 2 random colors and scrambled graphics.
   Typically the 2 random colors are dark blue and black.


4. A FAILED motherboard will likely power on with a blank (black) screen.

   Watch the dual display initialization, NOT the TV screen, after powering on
   the motherboard.

   A. Balcheck will NOT initialize.

      The dual display will not initialize to - - (dash dash) and count up. A
      failure is preventing Balcheck from executing. The failure is likely a
      motherboard Zone A or B failure. See Notes below.

   B. Balcheck reports an error on the dual display.

      The typical error code reported will be 04, a video data line/RAM error,
      indicating a motherboard Zone C or D failure. An error code 04 is
      reported immediately after Balcheck is initialized. In this case,
      run SetScreen3 to see if Zone C is operating and to further investigate
      the code 04 error. See Notes below.


Notes

For more info, reference the following BalcheckHR user manual docs:

1. Standard Balcheck Tests

2. Error Reports

3. SetScreen3

4. Optional Troubleshooting Programs


MCM Design's motherboard Zones A thru E descriptions are listed in the doc
"Miscellaneous Text Docs".




End of document
MCM Design
DEC 2018