I am in the UK.

I have been cleaning out the dust from the inside of my monitor and I
just moved a few pots to make sure their tracks are clean and returned
the pots to how they were.

In fact the only pots I can find are three right next to the coil on the
neck of the picture tube and they are marked:

Y-HC: Y and in small letters, HC
Delta V: capital delta symbol then V
YV: Y and in a small letter, V

What do these do?

To be prfectly honest I think I may have not quite returned them to
their original postion but might be 20 or 30 degrees out.

Can I adjust them with the monitor on? Of course I won't be touching
any HT parts but I wonder if they are inherently too close to the HT to
adjust while the monitor is on?

Must I use an insulated trimming tool rather than a meta scredriver?

Years ago, my Dad, a learned professional and well respected in his
field, told me this story when I was a boy.

One day he was sitting with all the other well respected learned
professionals in the lounge in the building where they worked.

They had just gotten a new and very expensive piece of equipment
installed, and the installer was training them in the procedures for
using their new equipment.

The equipment was a COLOR television. The first one that many of the
people in the room had ever seen.

After the speech, asked the respected learned professionals in the room
if they wanted the absolute best color picture they could get on this
tv. "Well, of course.", somebody replied.

The installer opened a little door in the front of the device and
pointed to a little row of colored knobs he'd just finished adjusting.
See these little knobs here?

In rapt attention, they all stared...yes..

DON'T F*** WITH THEM.

"Andy" wrote in message
...
I am in the UK.

I have been cleaning out the dust from the inside of my monitor and I
just moved a few pots to make sure their tracks are clean and returned
the pots to how they were.


EEK, if it ain't broke, don't fix it.

One of my first childhood 'accidents' was messing with the myriad of
alignment pots which were too easily accessable on the back of our old
Philips colour TV.

Moving pots which have not been touched for years can also cause problems
and can crack an old, seized shaft or rip up the carbon track.....

//Clive.

"Andy" wrote in message
...
I am in the UK.

I have been cleaning out the dust from the inside of my monitor and I
just moved a few pots to make sure their tracks are clean and returned
the pots to how they were.


With respect, that was an extremely foolish thing to do. If you don't
understand the inside of mains operated equipment, you shouldn't be inside
it, let alone turning adjustments. If the pots had been dirty but producing
no symptoms, turning them could have caused a fault that wasn't there before
by dragging the dirt under the wiper.


In fact the only pots I can find are three right next to the coil on the
neck of the picture tube and they are marked:

Y-HC: Y and in small letters, HC
Delta V: capital delta symbol then V
YV: Y and in a small letter, V

What do these do?


They are convergence pots. They alter the relationship of the geometries
between the beams. The red, green and blue images which make up the colour
picture on your monitor must overlap as close to perfectly as possible,
otherwise you will see red, green or blue fringes on different parts of the
image. They should only ever be altered by someone who understands how to
set them up- they can be very difficult to get back if you don't know what
you're doing.

If the picture looks OK, you've got away with it.

At least you didn't alter the static convergence rings on the CRT neck- that
really would have caused problems.

Dave

On 02 May 2006, Dave wrote:

They are convergence pots. They alter the relationship of the
geometries between the beams. The red, green and blue images which
make up the colour picture on your monitor must overlap as close to
perfectly as possible, otherwise you will see red, green or blue
fringes on different parts of the image. They should only ever be
altered by someone who understands how to set them up- they can be
very difficult to get back if you don't know what you're doing.

If the picture looks OK, you've got away with it.


Phew!



At least you didn't alter the static convergence rings on the CRT
neck- that really would have caused problems.

Hmmm. Let me have a look and see if I can move .... :-)

Andy writes:

On 02 May 2006, Dave wrote:

They are convergence pots. They alter the relationship of the
geometries between the beams. The red, green and blue images which
make up the colour picture on your monitor must overlap as close to
perfectly as possible, otherwise you will see red, green or blue
fringes on different parts of the image. They should only ever be
altered by someone who understands how to set them up- they can be
very difficult to get back if you don't know what you're doing.

If the picture looks OK, you've got away with it.

Phew!

At least you didn't alter the static convergence rings on the CRT
neck- that really would have caused problems.

Hmmm. Let me have a look and see if I can move .... :-)

Everyone loves to diddle with those magnet rings....

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Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Andy wrote:
I am in the UK.

I have been cleaning out the dust from the inside of my monitor and I
just moved a few pots to make sure their tracks are clean and returned
the pots to how they were.


Totally unnecessary operation but as you've fiddled now, it can't hurt
to mess around with some insulated tools and some safety knowledge.
Track down the Sci.Electronics.Rapair FAQ site and read.. (or skip the
monitor if the picture is bad, and get a better one from freecycle.org)

Long time ago a friend bought (then) a quite nice secondhand VHS video
recorder (JVC 3V43) with HiFi heads, still frame advance and all the
toys. Plugged it into his television set and noticed the picture tearing
across from the top. So he 'fixed' it. Took the VCR covers off, got some
sand paper, scrubbed the head drum - found 4 black specks wouldn't
shift. So took a screwdriver and neatly chipped them away...

Yes, this idiot computer programmer's TV was to blame (time constant not
set for VCR) but the video head was now completely beyond service - and
cost to replace as much as the whole recorder cost him :-(

--
Adrian C

Adrian C wrote in
:

Long time ago a friend bought (then) a quite nice secondhand VHS video
recorder (JVC 3V43) with HiFi heads, still frame advance and all the
toys. Plugged it into his television set and noticed the picture
tearing across from the top. So he 'fixed' it. Took the VCR covers
off, got some sand paper, scrubbed the head drum - found 4 black
specks wouldn't shift. So took a screwdriver and neatly chipped them
away...
Yes, this idiot computer programmer's TV was to blame (time constant
not set for VCR) but the video head was now completely beyond service
- and cost to replace as much as the whole recorder cost him :-(

LOL

I'm in two minds as to whether to dismiss this story as apocryphal or to
accept that there really *are* people who would do this!

I once managed to resurrect my old VCR which started producing *very* snowy
pictures after a tape got jammed inside it and must have shed some oxide
onto the heads. However that was with the aid of a cotton-wool ear-bud
soaked in isopropyl alcohol and very gently stroked over the heads - and
only after a head-cleaning cassette had proved to have no effect. The amount
of crud that came off was quite remarkable. After allowing time for the
alcohol to evaporate (I didn't want the tape sticking to the drum!) I
gingerly fired up the VCR and the picture improved over the course of a few
minutes' playing. After a bit longer, the hi-fi sound came back as well.

But to attack a video head with sandpaper and a screwdriver... gulp!



I'm firmly of the school of thought that says "look as much as you like, but
if it's not broken, don't try to 'fix' it". And when EHT is involved, I'd be
very reluctant to open the case of a monitor, even after it's been switched
off for a while - capacitors can store lethal voltages. If I was going to
attempt to tweak the pots, I'd use a long nylon screwdriver and I'd just
tickle each pot in case the setting was very critical. To be "almost right,
but maybe 20 or 30 degrees out" sounds rather vague.

"Martin Underwood" wrote in message
...
I once managed to resurrect my old VCR which started producing *very*
snowy pictures after a tape got jammed inside it and must have shed some
oxide onto the heads. However that was with the aid of a cotton-wool
ear-bud soaked in isopropyl alcohol and very gently stroked over the
heads - and only after a head-cleaning cassette had proved to have no
effect.

Cotton buds should not be used on video heads IMO. The fibres can snag and
break off the heads, or become entangled. There's only two things I ever put
near the drum to clean it- chamois swabs and copier paper, both with
isopropyl alcohol. Both clean the heads very well indeed, and even dry
copier paper does a safe job if one doesn't have the proper tools handy.

Dave

"Adrian C" wrote in message
...


Yes, this idiot computer programmer's TV was to blame (time constant not
set for VCR) but the video head was now completely beyond service - and
cost to replace as much as the whole recorder cost him :-(


Reminds me of when I walked into a friends room to find him armed with a
carving knife in one hand and the bezel of his computer monitor in the
other.

Turned out he had a computer game with some text which scrolled at the very
bottom on the screen and was partially obscured by the CRT surround which he
intended to carve away. I quickly pointed out the V-height pot at the back
of his monitor but it took hours to rebuild it as to get the bezel off he
had unplugged every cable and HT lead he could see.

I really am surprised we don't see more people electrocuted whilst messing
around in the back of TVs and monitors...

//Clive.

Couldn't this also have been a result of the VCR's back tension being out of
adjustment or was this occuring only with the regular cable signal?

Bruce


"Adrian C" wrote in message
...
Andy wrote:
I am in the UK.

I have been cleaning out the dust from the inside of my monitor and I
just moved a few pots to make sure their tracks are clean and returned
the pots to how they were.


Totally unnecessary operation but as you've fiddled now, it can't hurt to
mess around with some insulated tools and some safety knowledge. Track
down the Sci.Electronics.Rapair FAQ site and read.. (or skip the monitor
if the picture is bad, and get a better one from freecycle.org)

Long time ago a friend bought (then) a quite nice secondhand VHS video
recorder (JVC 3V43) with HiFi heads, still frame advance and all the toys.
Plugged it into his television set and noticed the picture tearing across
from the top. So he 'fixed' it. Took the VCR covers off, got some sand
paper, scrubbed the head drum - found 4 black specks wouldn't shift. So
took a screwdriver and neatly chipped them away...

Yes, this idiot computer programmer's TV was to blame (time constant not
set for VCR) but the video head was now completely beyond service - and
cost to replace as much as the whole recorder cost him :-(

--
Adrian C

Bruce H wrote:
Couldn't this also have been a result of the VCR's back tension being out of
adjustment or was this occuring only with the regular cable signal?

Nope. He got another video recorder and complained of the same problem.
Didn't take us long to figure out what was up - around the mid
eighties it was fairly common knowledge (here in the UK anyway) that one
of the UHF preset channels (normally the last one of 4 or 8) on a TV set
was reserved for VCR use - he'd used another.

--
Adrian C

In article ,
Adrian C wrote:
Bruce H wrote:
Couldn't this also have been a result of the VCR's back tension being
out of adjustment or was this occuring only with the regular cable
signal?

Nope. He got another video recorder and complained of the same problem.
Didn't take us long to figure out what was up - around the mid
eighties it was fairly common knowledge (here in the UK anyway) that one
of the UHF preset channels (normally the last one of 4 or 8) on a TV set
was reserved for VCR use - he'd used another.

The last channel selector altered the time constant in the line sync
locking so that it could cope with unstable vcr signals.

--
From KT24 - in drought-ridden Surrey

Using a RISC OS5 computer

charles wrote in
:

In article ,
Adrian C wrote:
Bruce H wrote:
Couldn't this also have been a result of the VCR's back tension
being out of adjustment or was this occuring only with the regular
cable signal?

Nope. He got another video recorder and complained of the same
problem. Didn't take us long to figure out what was up - around
the mid
eighties it was fairly common knowledge (here in the UK anyway) that
one of the UHF preset channels (normally the last one of 4 or 8) on
a TV set was reserved for VCR use - he'd used another.

The last channel selector altered the time constant in the line sync
locking so that it could cope with unstable vcr signals.

What was the disadvantage of of using the VCR time constant setting for
off-air reception? Presumably there must have been a disadvantage otherwise
all the channel positions would have been permanently set to the VCR time
constant.

I know my TV (bought in 2000) has different settings on its SCART sockets
than on its phono and S-Video aux inputs on the front panel: the phono and
S-video sockets have more problem locking onto the video output from my
laptop which evidently isn't quite 625/50 specification, whereas the SCARTs
are much more tolerant.