"d6xkr via ElectronicsKB.com" u45258@uwe wrote in message
news:883aeb25e685c@uwe...
Arfa Daily wrote:
hi

[quoted text clipped - 43 lines]

thanx

Seems to me that the advice being given on that forum, whilst not
definitive, is never-the-less exactly right. I would suggest that the
first
thing to do would be to check the pincushion amp, and its drive. Also, if
any caps *have* leaked (and you are not confusing the glue that's often
found around their bases, with leaked electrolyte), then they need to be
replaced. Just because they had enough go in them to just about do their
job
three days ago, doesn't mean that one of them hasn't gasped its last
today.

To use a car analogy, you can drive around today with half a millimetre of
lining material on your brake pads, that stop the car today, and squeal
metal on metal tomorrow ...

The 24C08 is an EEPROM, where all of the setup parameters are stored. It's
not at all unusual for these to get corrupted in TV sets, and to produce
symptoms like you describe, which are not correctable. However, it's often
necessary to pre-program a new blank one with a basic set of parameters,
before it will work.

Finally, a warning. If you are not used to working on monitors, take
extreme
care, as they employ switchmode power supplies, which are (literally)
potentially lethal. Also the high voltage generation circuits for the CRT
can give you a nasty bite, as can the CRT itself, long after you have
switched off.

Arfa



hi and thanx for your reply.....

i'm sorry my post didn't show the fourth chip which is;

4. KA3842B and also there was a fifth one......
E009C

i wrote it's data on the back of the paper containing all the data of the
chips i found, it's data are;

5. PM02AF
LM this one i couldn't get any datasheet about
358N

the fourth chip is smps controller, this makes me know only three out of
five
chips and i don't know exactly which is the pincushion amp, or where is
it's
drive. it's kind of making me handicaped not having the service manual for
this piece of hardware. also i don't have the proper test equips, only an
avo
meter, the data sheets and my personal experience.

today i replace the caps that i suspected of having leaked, and the truth
to
be said, the pincushion became less by 8mm which is small but positive
result.
also i tried to replace the ATMEL 24C08 EEPROM with a new blank one, but i
got a white screen with horizontal bright lines across it, it looked like
a
writing paper and i didn't see any thing but shadows of what really was to
be
shown behind this new look so i turned back to the old one and every thing
is
fine relatively.

the first chip i mentioned "no. 1" is a big ic and since the begining i
suspected it but i don't have it's data sheet as to decide whether or not
to
replace it. also it's said to be discontinued which makes me unsure
whether
will i find it on the market or not.

as a matter of fact the monitor is eight years old and all of it's
capacitors
are probably if not surely much older, so it needs all of it's caps to be
replaced. but i need to have it working as not to be throwing mony away
for
nothing.

you are right about being extra careful while working with this type of
hardware, but the smps isn't what i fear. what really makes me sweat my
juices out is the tube itself, when i'm working on it while online i know
that there is a 25+ kv infront of me. one mistake and i might be history
and
so i take emergency precautions while working with it. also i have proper
grounding which calms me down a little.

this is all i've got,

hope for the best solution.


thanx all

--

Looking at www.eserviceinfo.com there are a lot of entries for Viewsonic
manuals. I only had a quick skim through, but there seemed to be lots of
listings for the e655 model which might be sufficiently similar to work by
??

The pincushion amp is likely to be discrete rather than a chip, and might be
based around FET on a small heatsink. Geometry correction waveforms are
often fed to it from that 'big' chip. I fear that you will not get too far
on this fault without a 'scope to look at the waveforms. I would absolutely
recommend against employing any kind of 'shotgun' approach at component
replacement, as you are likely to end up with more problems than you started
with.

As for the safety angle, I think you might be misunderstanding the relative
dangers of the HV generator circuitry, and the power supply. Whilst it is
true that the CRT's final anode will have around 25 kv on it, the source
impedance for this supply is relatively high. This means that the available
current at that voltage is quite limited. For sure, if you had a weak heart,
or managed to hang yourself right across that supply, receiving a shock from
it *might*, at a pinch, prove fatal. The much more likely outcome is a
stinging hand - probably with a cut across it where your hand collided with
the chassis during its rapid exit :-) - some words that are completely
new to your children :-) and wounded pride.

On the other hand, the switch mode power supply has around 380v dc on its
front end, and this is derived DIRECTLY from the incoming line voltage by a
bridge rectifier, so a relatively low impedance source with the current
limited *only* by the front end fuse, which is likely to be a 3 or 4 amp
ceramic type. This is enough to kill you. No joke. Fact.

So please take care around that area. Use an isolation transformer if you
have one. Makes life a little bit safer.

Arfa