Philips DVDR985 Technical Training Manual page 110

lator. The RF signal merely loops through. Tuner
operation needs to be checked on the Video
Outputs.
No Tuner Functions
As with any circuit, verify the supply voltages.
The 33Vdc supply is used exclusively by the
Tuner. Check for the presence of the I 2 C Buss
on the Tuner. This signal controls the operation
of the Tuner. If those two conditions are met,
there should be IF going to the demodulator IC.
If possible provide a substitute IF signal to check
the Demodulator IC. If substitution shows the
Demodulator is good, replace the Tuner. If no
substitution is available, Noise can be introduced
into the IF signal path. The demodulator should
show a change in the output.
Erratic Tuner Function
Problems described here usually are: the Tuner
drifts or won't lock in, certain bands of the Tuner
do not function. or, the picture is snowy. Slow
lock in or continuous hunting for lock in is usually
the SAW filter, 1701. In rare cases, the AFC
Adjustment will cure it. If both of those have
been tried, check or replace the components on
Pins 6,7,18, and 19. If no results are achieved,
replace the Demodulator IC before the Tuner.
When it is proven that the Demodulator IC or cir-
cuits to follow are the problem, check for Video
on Pin 16 for Video. This assures us that the
problem is here and not further down the signal
chain. Most of the components around the
demodulator IC are passive. The IC is the main
suspect. You should prove the IC is bad before
replacing. Using an ohmmeter, check every pin
of the IC to ground, looking for a short or near
short. If nothing is found, it is reasonable to con-
sider the IC bad.
Basic Engine
If the PSEN signal is not present, there is a
problem in the BE that will interfere with the unit
powering up. Other symptom caused by the BE
can be playability and Recording Problems.
No power up involves the MACE3
Microcomputer. It is the System Control for the
BE. Like any microcomputer, first check the sup-
plies, the Oscillator, and the Reset to the IC.
Then check for the SUR line. It Goes low after
the MACE3 checks its memory. If it doesn't go
low, the MACE3, the SRAM, or the Flash Rom
are bad. If the MACE oscillator is present, at
least part of the Chip is functioning. Check for
data on the Flash ROM. It is read first. If there is
activity, suspect the SRAM. If there is no activity
on the FLASH suspect the Flash ROM as bad.
If the Symptom has in the display three words
repeating" Opening, Closing, Blocked", the prob-
lem is likely the OPU. Those three words could
appear when a tray motor problem is occurring,
however, the OPU is a much more common
occurrance.
There are many symptoms that involve playabili-
ty, and recordability. Most common is that the
unit will not recognize a disk, or a certain type of
disk. Sometimes the symptom is that the unit
writes or reads for only a few minutes then an
error is shown in the display. Another is that the
unit has a problem during the Menu update. All
of these symptoms and more are usually caused
by a bad OPU.
Edit Problems and Chapter problems have two
issues to be resolved. One is the software.
There have been many updates to the System
software. Many of the updates were designed to
fix those kind of issues. FF12p is the current ver-
sion to be loaded. If the Software upgrades does
not fix the problem, It is likely the OPU is the
problem.
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