I have a 2 year old portable TV where when switched on occasionally the
screen will go blank, but power is still on and sound still comes
through the speakers. More recently the screen doesn't come on at all
when switched on, though the power light is on and again sound is
coming through the speakers. We found that when the screen went blank
if we lightly tapped the sides of the TV the picture would sometimes
Rather than mindlessly going out and buying a replacement I'd rather
open the TV up and see if there is anything that I can fix - has a
cable come loose, a part can be replaced etc ... ? But I've done no TV
DIY before so I'm not sure where to start.
The TV is well looked after, i.e. for the duration of the time that
we've had it it's simply been placed on a wall mounted TV stand, so
it's not as if it's been knocked about.
I've googled this group but can't find any immediate obvious answers to
similar problems. Any pointers please?
What's a dry solder joint? :) (I'll google that)
I've checked this link out (posted by someone below)
http://www.repairfaq.org/samnew/tvfaq/tvblankpic.htm and I'm guessing
the raster there is no power to the raster (whatever that is! :)
because there's no picture at all and there is no sound like there is
when there is a picture.
I have a couple questions:
1. how would I identify a dry solder joint and how would it cause a
lack of power?
2. regarding voltage, surely if I unplug the TV there'll be no voltage
to worry about?
It is a solder joint which is not making full and proper contact
between the two parts it is intended to connect. A poor or intermitant
connection in other words.
The raster, is what makes the spot on the screen move across the
These can be difficult for even the expert to spot. Personally, with
your described fault - I would be working with the set live and the
back off - tapping PCB', components, connections and wires with
something insulated, hoping to reproduce the fault and thus hope to
help localise it. Then you get the magnifying lense out to inpect the
The fault you are describing - The loss of whistle + loss of picture
would lead me to the line timebase area and probably the EHT unit. If
you are really determined to have a go yourself - Look for a PCB upon
which is mounted a large component soldered on to the PCB by an almost
circular ring of perhaps 8 to 10 connections. To further confirm you
have the right part, you should be able to trace the EHT lead back from
the tube to the same component. At the tube end it will disappear into
a large insulating cover.
Check out the 8 to 10 soldered connections and you may well find one or
more of these has been burnt and making poor contact with the PCB.
The TV can store the high voltages for quite some time after it has
Switch off TV and turn setupside down, if you can see the PCB? this is the
soldered(printed circuit board), get some methylated spirits, tooth brush,
and a magnifying glass, locate the EHT transfomer area(big black thing on
other side of board), rub meths on soldered joints with tooth brush and
wait till it drys out, then get magnifying glass and look over the joints
they will be greyish now and any dry joint will show as greyish with a thin
black circle in the joint...this is a dry joint.
*The* nightmare service problem.
dry joints are usually microscopic cracks in the printed board copper or
progressive corrosion in a badly soldered joint. Multilayer PCB's may
have been used which hide everything.
Integrated circuit chips can also develop internal connection problems
with similar symptoms in which case replacement is necessary. The chips
may be difficult to obtain outside the trade and need special tools to
In any case dry joints are not usually visible unless you're extremely
lucky. Mechanical pressure or tapping is required to locate. Even
then they may be next to impossible to find. If an intermittent fault
can't be repeated at will, it can't be repaired.
The most dangerous voltage is about 25 KV on the back of the picture
tube which could cause cardiac arrest if it goes through the body trunk,
especially for an older person. This voltage can persist for weeks even
when the TV is switched off and unplugged and must be discharged before
doing anything. It will damge either yourself or do in the rest of the
electronics if it discharges where it shouldn't.
Sorry - that sounded a bit flippant, but it was meant seriously.
If I walked into a car mechanics, and told them my car had stopped working,
but I had hear of some thing called "an injection", but wasn't sure what it
looked like, so pulled a few bits out of the engine with a hammer, and could
they just tell me how to recognise whether the "injection" I pulled was worn
or not, then I'm sure I'd not be taken seriously.
Some thing applies to TVs. As well as very high voltages, that can can stay
in the set for *days* and can *kill*, a TV set is a very complicated thing.
The problem probably is just a dry joint, but identifying it, fixing it, and
not bugg*ring up the whole insides of the thing, and putting it back
together *safely*, as an absolute beginner, is only going to end in tears.
Take it back - it should last longer than two years. Make a fuss - you have
nothing to loose ;-)
Almost certainly a dry joint - but you might well electrocute yourself while
trying to fix it if you don't know what you're doing.
If it's only 2 years old, take it back to where you bought it and get them
to fix it for free. Forget the maker's guarantee - which is probably only a
year - and invoke your common law rights!
Tell them that they have a legal obligation to supply goods which are of
merchantable quality. This TV clearly wasn't - since any reasonable person
would expect it to last more than 2 years without failing.
Google for Sale of Goods Act, et al
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