Philips DVDR985 Technical Training Manual page 108

The Front Panel/ Display Board
Problems on the Front Panel display fall into four
categories: no display function, improper display
function, no keyboard function, and no remote
control function. Do not consider this board at
fault first if all of the symptoms are present. The
front panel cannot operate until many functions
of self-check pass. A problem on this board more
likely shows one of the above symptoms.
The board has several power supply voltages
that should be checked first before considering a
problem on the board.
No display
There are three major elements to work with for
no display: the florescent tube, the
Microcontroller and the power supplies dedicated
to the tube. The VGNstandy supply is only used
by the tube. There is a special switching supply
on the Front Panel that supplies filament for the
tube.
If the keyboard is operating, the microcomputer
is at least partially functioning. Check the dedi-
cated power supply. If it seems normal, check
the scanning signals for the tube with a scope. If
the supplies are proper and the scanning signals
are present, replace the tube. If the scanning
signals are not present, the microcomputer
becomes suspect.
Improper display
The self diagnostics have a test pattern routine
that can help when troubleshooting this type of
failure. One of the choices is to light up all of the
segments. Set this up to show you what seg-
ments are not functioning proper. A pattern
should be visible. One row or a column may not
be lighting up. Trace out the pin that is responsi-
ble for the row or rows that are not lighting.
There are diodes connected to these pins.
Normally the diode(s) are bad or there is a for-
eign substance on the board at that location.
No keyboard function
It takes four Microcomputers to function properly
for the keyboard to function: the Microcomputer
on the Front Panel, the microcomputer on the
Analog Board, and two microcomputers on the
Digital Board. If the display is working, the Front
Panel should be showing four dashes. This
means the Power up Reset and self check has
passed. Check for remote operation. If the
remote functions, start with the Analog Board's
microcomputer. Monitor the I 2 C Bus while press-
ing the keyboard. The data should change. If it
does, the problem is definitely on the Analog
Board. If the I 2 C bus does not reflect a change
in data when a key is pressed, check the RTL
logic for the keys on the Front Panel. If the
Keyboard data seems to be getting into the
microcomputer, check the secondary switched
supplies. The ISTBY goes Low to turn on the
SW5 and the SW 8Vdc supplies as part of the
last step in power up.
No Remote Control Function
It takes two Microcomputers to function properly
for the Remote control to function: the
Microcomputer on the Front Panel and the
microcomputer on the Analog Board. If the dis-
play is working, and keyboard function are nor-
mal, the Front Panel Microcomputer and the rest
of the unit is operating properly. Start with IR
receiver's output. The signal should be TTL
level. If it is not, be sure the connections are
good, supplying the B+ and ground to the
Receiver. If the signal is there, check for it on the
Front Panel's Microcomputer, Pin 2. If it is miss-
ing check IC7160 and its support components.
If the signal going to the Front panel
Microcomputer is proper, monitor the I 2 C Bus
while pressing the remote keyboard. The data
should change. If it does not, check all the vitals
to the Microcomputer, VCC, grounds, Clocks,
and reset the microcomputer as a test. If none of
these yield results, suspect the microcomputer.
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