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Jerry Greenberg
 
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Default Repairing new TVs isn't easy

You are very accurate in your comments. As for your particular set, it
is possible to get one that will last, while the majority did give
problems. The engineering behind the set is good, but the component
construction standards had some faults. As there are tolerances in
components, there are also tolerances in the actual MTBF (Mean Time
Between Failure).

The new TV sets, home entertainment equipment, and new appliances, are
very sophisticated. Yes, it is true that many of the faults cannot be
serviced without the proper qualifications, the training, service
manuals, and the proper test and calibration equipment.

The older tube sets were very simple in their construction. Most of
the faults could be fixed using simpler tools, and basic instruments.
The early solid state TV sets started to get very difficult to service
compared to the tube sets. They did not use high density surface mount
components, with multi layered circuit boards, and very close
proximaty soldering. There are now many components used where the lead
spacing is 1/100 of an inch. It is impossible to work with a soldering
iron of any kind with this tolerance.

As for the adjustments of the new sets, there are very few pots or
trimmers used. They only use pots and trimmers where they cannot do
the task by software control.

All the functions and setups are done by software. Some models have
the capability to do many of the setups through the remote control,
while others require a PC interface with the factory software. For
many of these setups, the proper calibration generators, scope, and
DVM is required. Only a few of the adjustments are done visually, such
as the pin cushioning, and scan parameters.

The only type of service the avid home electronics hobbyist can do is
to re-solder a cold solder connection if can be done with a home
soldering iron, change a part that can be soldered with an affordable
home soldering tool, or fix something obvious.

The expensive sets are serviceable, but are costly to service. In
actual fact, many of the faults cannot be serviced even in the small
shops. Troubleshooting the sets to locate the faulty parts can be
extremely difficult. Many of the small shops are subcontracting out
the work, and charging a small fee on top of their cost for handling.

The new generation of sets are microprocessor run, and use a number of
function IC's that contain processors to operate. These all talk to
each other through a multiplexed data and address buss. To read these
processors and know what is going on is very complex, and cannot be
done without the proper equipment.

There are very many safety issues when working in these TV sets. The
CRT type use very high voltages, and the current drives used is also
very high. The newer sets have very high brightness output from the
CRT. This takes a very intense drive to the tube to do this. The high
voltage at the CRT in the older sets was typically about 19 to 25 Kv.
Many of the new large screen sets are up to about 27 to 35 Kv. The
current at the HV output is also much higher to feed the load of the
tube. The basic supply also has to be of a high enough current to
supply this. The new sets can be deadly dangerous to work on, if you
do not know what you are doing!

After changing safety critical parts, such as in the power supply and
high voltage sections, there are some safety checks that must be done.
If these safety critical areas are serviced, and not properly checked
there can be issues such as too high X-Ray emissions, and or excessive
electromagnetic RF radiation. The X-Ray emission is a dangerous issue
where the user can never feel this, but it may be harming the people
that are in the vicinity of the set. The electromagnetic radiation
harm at the levels in a TV set are still controversial, except for
exposure to pregnant women.

After the set is serviced, the proper safety tests must be verified,
including the AC power isolation test. If the set is not properly
isolated to the user controls, and rear connections, the user can be
injured when connecting something to the set, or simply using it.

Most of the failures in TV sets are in the areas where the most
electrical stress is occurring. These are the power supply, scans, and
high voltage sections. These are the most critical for safety issues.
This is why I always tell people to take the set to a qualified
service rep for their set.

There are many people on these groups that are asking about how to fix
their sets who are not qualified to work on their sets, and have no
business doing so. They are making a danger to themselves, and to
their family, just to try to save a few dollars. It is very easy to
tell by the nature of the questions if the person asking is a
qualified tech or not.

I have seen questions, like "My set is dead, what is wrong?", or
"There is no colour, what part do I change", or "My picture is blurry,
what is wrong", or "There is a line down my picture, what is wrong",
and many other vague questions like this. Any TV or appliance is far
too complex to give a viable answer to fix it from such vague
questions. Just for curiosity if you ask for voltage readings, the
person doesn't even have a basic DVM, or any proper tools, or
knowledge to do the most basic checks, but the person has the rear
cover off, and is messing around inside the set!!!

Many times, in the end his set will cost far more to service, because
the home do-it-yourselfer does more damage than when the problem
started out. He also takes the risks of injury to himself, and or his
family.

Wait until the main stream TV sets are LCD, and Plasma types. This is
going to be a very big problem for the ones that want to try to stay
in the TV service business. Many of these sets will be serviced at
the modular level only. There will be very little service information
in the way of schematics. The service manual will be an instructions
of how to change the modules, and go through the testing and
calibration when necessary. Component level service will not be
supported. Servicing the TV set will be like servicing a PC computer.
For any adjustments when required, the proper equipment will be
required. Many models will require dedicated tools to work on,
therefore will be non-feasible to service outside of the factory
service.

VCR's are getting so low in cost, that if the machine is not a very
expensive recent model, it will not pay to even get an estimate on it.
A typical good quality home HiFi VCR can be bought for about $140 US.
Low cost ones can go for about $50 or so. If you were to evaluate
about 1 to 2 hours of labor, and the parts to fix it, the cost would
be very close to that of a very good new VCR. Then there is the factor
that if it failed, the unit may be a number of years old already. If
you calculate the age, verses the value, you come up with the fact
that the machine is not worth to service. You can put money in to an
older machine where there are more parts that statistically will soon
fail.


I said my point here...


Jerry G.

--



(Jeff Strieble) wrote in message . com...
The design of all new TV sets these days makes it impossible to repair
the set unless you are a qualified technician and have special tools
and equipment, to wit, a controlled-temperature soldering station (a
regular pencil iron or [gasp!] soldering gun won't work; you will
either make a poor connection if your iron is too small, or, at worst,
lift the foil off the PC board) and a bench full of other gear.
Thirty-plus years ago, I used to work on old TVs I'd rescue from my
neighbors' trash; these were mostly tube-powered sets with heavy metal
chassis, often handwired (e. g. Zenith, before Gold Star bought them
out) in those days, and often a new tube or two or a minor
adjustment--or even a small part, such as a capacitor or
resistor--would get them working without much trouble. Today, however,
all new sets are made with surface-mounted components, crowded circuit
boards, scan-derived power supplies, and other things the old sets
never had. That has put me, and many former electronics experimenters
like me, out of the picture as far as being able to repair our own
sets is concerned--and to be perfectly honest about it, I miss the old
days. Today, the only way to have your TV repaired is to call in a
qualified technician who has access to a repair shop full of equipment
and to pay their very often sky-high prices. By way of example, my RCA
XL-100 19" color set, which I purchased new in 1999, works quite well
now on cable. However, the set has been repaired twice for the same
problem. The repair was not covered by the warranty, so I had to pay
the TV shop out of my own pocket both times.

The other thing which keeps average (read most) set owners from
repairing their own TVs are all the safety interlocks, shields,
barriers, etc. that must be replaced just as they were removed from
the set, otherwise the TV could create a shock, fire or X-ray hazard.
Also, the manner in which parts are mounted on PC boards in all new
TVs absolutely precludes service by anyone other than qualified
technicians, not to mention the tests for safety hazards, etc. which
must be performed after any new set has been serviced for major
problems such as no high voltage, etc. Without such tests being
performed, the TV has not been properly repaired and, as I mentioned,
could be unsafe.

Television repair in the 21st century has been taken out of the
hands of set owners, who "repair" their sets these days by taking them
to high-priced repair shops. The problem is that most TV shops perform
only warranty repairs these days, and will not touch sets more than a
few years old. I have seen posts to this forum advising that owners of
such old sets (such as Zenith System 3 sets of the '80s and RCA's
original XL-100s from the '70s, et al.) scrap them at once and buy a
brand new TV. These days it is not uncommon to see RCA Guide Plus TVs
and Zenith System 3s, etc. from just a few years ago on treelawns and
curbs, all because the parts needed to repair them are NLA. It is no
longer practical to spend large sums of money on repairs to today's
RCA or Zenith TVs (unless they are the big projection or HD sets which
cost $1000 or more). The Zenith/GS sets are unreliable as all get-out
anyhow, with all their circuit problems, CRT issues and other things
which have been reported with them, and RCA is just as bad. I have a
Zenith 19" TV (SMS1917SG) which was new in 1995 and which still works
well today (I had it on recently and found it is working almost as
well as when it was new). No issues, yet, anyhow, with the CRT or any
other part of this set, or with the circuitry or CRT of my living-room
RCA XL-100.

I have a question, though. With all the comments I've read in this
forum regarding the poor reliability of Zenith TVs, and given the fact
that my 1995 Zenith SMS1917SG still works very well on cable for
having almost nine years on it (with the original CRT, which is still
working and producing a decent picture), I wonder. Did I just happen
to get a good set by the luck of the draw?

Thanks for reading this. Happy New Year.

Jeff Strieble, WB8NHV (mailto:
)
Fairport, Ohio