Philips DVDR985 Technical Training Manual page 109

The Digital Board
The Digital Board is central to the recorder's
operation. There are two categories of symptoms
that cause the Digital Board to be suspect. One
is "No Power" and the other is a more conven-
tional digital signal flow problem. The reason the
Digital Board needs to be focused on for a No
Power problem is that the I 2 C Bus Host is on the
Digital Board. The Host Decoder IC also pro-
duces secondary Reset function for many ICs
including the BE. If you are concerned with "No
Power" and the SMPS is functioning, go to the
No power part of this write up where all the cir-
cuits involved in power up will be discussed. For
digital signal path troubleshooting, proceed to
the next paragraph.
Close scrutiny of the symptom is necessary. If
you are considering the problem to be on the
Digital board, you have basic operation of the
unit. The unit powers up. The Front Panel's dis-
play is proper. The unit will try to play a disc. The
symptom involves: no menu, no playback Video
or Audio, no record Video or Audio, or scrambled
Video or Audio. If you can play a known good
disc, you can eliminate half of the circuitry in the
Digital Signal Processor. If you see the Video
and Audio during the record process, the Digital
Board is probably not where your problem is.
The parallel loop thru condition that occurs dur-
ing record utilizes most of the circuitry on the
Digital Board and the Analog Board.
If the problem is apparent in playback, use play-
back for troubleshooting. Use a disc that has
colorbars recoded on it. Check the CVBS signal
on the output of the Host Decoder. The Bars sig-
nal allows you to closely scrutinize the signal on
the output. If the signal is good, follow the signal
through the Analog Board to the output jacks.
If the signal is missing or distorted, check the DC
voltage on the Output Pin. If the DC voltage is
.5V or less, the signal could be loaded down.
Open the connection to the audio board to sepa-
rate where the problem is.
If the unit plays back properly, use the record
mode to troubleshoot. Most of the playback cir-
cuitry is in operation as well. The output of the
VSM supplying the BE is in the middle of the cir-
cuitry on the Digital Board. Check the Digital
Video stream here. If it is not present, check for
it going to the Empress. If it is there, the problem
involves the Empress and/or the VSM. If the sig-
nal is not present on the inputs to the Empress,
check the inputs to the VIP. If the signals are
there, stay on the Digital Board, checking for
problems with the VIP and/or the Empress. If the
signals are not coming into the VIP, the problem
is on the Analog Board. For all of these checks
you are looking for clean digital transitions of the
signal.
The Analog Board
The Analog Board can display many symptoms.
There are three main categories to consider
when looking for a problem on the Analog Board:
no Power, one or more function inoperative, or a
Video/Audio switching problem. If you are work-
ing with a No Power problem, go to the No
Power portion of this write up. If you are working
with a single function that is not operative, trace
the control of the function to the System Control
IC. For a Video/Audio routing issue, continue
with the next paragraph.
It has many inputs and outputs. It contains the
Tuner function. Symptoms for this module will
be: one or more type of output is missing, or the
Tuner does not function properly. Each of the
inputs and outputs have separate paths in and
out of the module. They all, however, pass
through the massive switch, IC7507. The key to
an input/output problem will be determining
which inputs and outputs are affected. If it is a
single signal, follow that line through the circuitry
to determine where the signal stops. If more than
one signal or all the signals are not passing
through the board, 7507 is the place to start.
Tuner problems
This symptom involves two major components,
the Tuner and the Demodulator IC7703. Tuner
problems fall into two categories: no Tuner func-
tion or erratic Tuner function. Be-aware: the RF
block on the unit does not contain an RF modu-
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