"Bert" lijbertv_at_xsinet_dot_co_dot_za wrote in message
...
Highly probable you actually have a fault in the tele rather than someone
dicking with the service menue. Suspect some of the passive components
around the vertical output, the output itself, etc. post the operational
potentials of the ic when in operation.
"Bert" lijbertv_at_xsinet_dot_co_dot_za wrote in message
...
Hello all
Problem with above Samsung, the bottom third of the screen is not there.
Replaced the vertical output IC TDA8356, still the same.
The drive signals coming from the TDA8842,pin 46 and 47, only one is
there,
the other one is just a dc level.
It is possible that someone was in the service menu and did change the
vertical settings.
Will try to get the original remote, which I do not have.
Anyone know how to come in the service menu and which options to change.
Thank you very much for any reply
Bert.



Thanks for the reply Art.
Pin 1 of the TDA8356 has got a nice sawtooth.
Pin 2 of the TDA8356 has a dc level of about 4 volt.
The dc lines are clean and the right value according to the datasheet.
The 2 outputs are there, but the positive and negative outputs do have a
flat part when showing on the scope
Did download the datasheet of the TDA8842, the same I do measure on pins
46
and 47.
I do not know if it is possible to adjust the linearity and shift so far
that one of the outputs is only a dc level.
Only problem is the 8842 is quite expensive but it seems I do have to get
one.


Firstly, playing Devil's advocate here, you already replaced the chip, why
would another new chip solve anything? How many chips would you buy until
you either give up the job or conclude, correctly, that the fault is
elsewhere? It's possible, though not highly likely, that the replacement was
DOA, but if it is dead, it is more likely that it was killed by fitting it
into a circuit with other faults.

How do you mean the bottom third is not there? Are you saying the picture
has normal proportions, but the bottom is black, or do you mean the bottom
of the picture is squashed and distorted? If it's the former, the fault is
not necessarily in the vertical output circuit. If it's the latter, try
changing electrolytic caps in the vertical output circuit. Given the low
cost of electrolytics, it's not a bad idea to replace them as a matter of
course when replcing the vertical output chip, as bad ones can destroy the
new chip. After all, electrolytics are probably the least reliable
components there are.

One thing is certain, making adjustments to attempt to cure the fault is a
*very* bad idea. You cannot adjust faults out, you have to repair them!
Making adjustments now then finding you have to make a repair afterwards
will make a satisfactory job a real hassle, or worse still, cause more
damage.

Dave