15 Jul
2004
15 Jul
'04
5:09 a.m.
Hi,
I have an old B&W "specialty" monitor which recently stopped working.
In the process of moving it around (to/from repair place) I noticed a
little black "tube magnet" dropping out when I took the cover off.
At the time I didn't think much of it (those in the know can chuckle now).
So, after a bout of replacing bad caps with no luck, I eventually broke
down and replaced the deflection board and the monitor sprang to life.
Much joy.
(note: "specialty" = designed for a specific computer with a special ECL
video connection and has no standard connector or interface. and no
schematics)
So, monitor is working. I proceed to adjust the H & V size, linearity, etc...
I notice that the bottom and sides will square up nicely but the top
edge has a large "dip" in the middle. No amount of trimmer fiddling will
fix this.
light goes off. "found" tube magnet is part of yoke assembly.
So, I notice where the missing magnet came from. Naturally it's on the
top side of the yoke assembly.
But - the "tube" has broken into 3 pieces (it was broke when I found it.
honest). I carefully glued it back together (no glue in the joints,
however) and replaced it. This helped a little but did not cure the
problem.
[note to reader: I never took that fields course. I know nothing of magnets.]
So,
- is a broken magnet pushed back together not as good as a whole magnet?
(strength wise)
- can I get a new magnet somewhere?
- is there anything special about these magnets?
- do normal monitor repair guys just have a box of these laying around?
- does this sort of thing happen all the time?
-brad
15 Jul
15 Jul
5:26 a.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
>>>> "Brad" == Brad Parker
<brad(a)heeltoe.com> writes:
Brad> Hi,
Brad> I have an old B&W "specialty" monitor which recently stopped
Brad> working. In the process of moving it around (to/from repair
Brad> place) I noticed a little black "tube magnet" dropping out when
Brad> I took the cover off.
Brad> So, I notice where the missing magnet came from. Naturally
Brad> it's on the top side of the yoke assembly.
Brad> But - the "tube" has broken into 3 pieces (it was broke when I
Brad> found it. honest). I carefully glued it back together (no
Brad> glue in the joints, however) and replaced it. This helped a
Brad> little but did not cure the problem.
Brad> [note to reader: I never took that fields course. I know
Brad> nothing of magnets.]
Brad> So,
Brad> - is a broken magnet pushed back together not as good as a
Brad> whole magnet? (strength wise)
Brad> - can I get a new magnet somewhere?
Brad> - is there anything special about these magnets?
It's probably not a magnet, but rather a ferrite core. You'd know the
difference putting the pieces together -- if you feel no attraction or
repulsion, it's not a permanent magnet.
A broken & repaired one is just fine so long as the gaps are tight.
If you create an airgap -- with or without glue -- that will change
the characteristics.
For a repair like that I'd consider the thin (not gap filling)
superglue.
Brad> - do normal monitor repair guys just have a box of these laying
Brad> around?
Maybe, but it wouldn't necessarily fit.
Brad> - does this sort of thing happen all the time?
It's never happened to me...
As for the problem, I wonder if the issue is that the core is in the
wrong spot. It's part of the deflection magnetics assembly, and if
it's misplaced then you'd certainly get problems like you describe.
Take a look at the corresponding piece at the bottom of the yoke. I
would expect things to be symmetric. The fact that the thing fell out
suggests that it may have been out of position, and when you pushed it
back in you may not have gotten it back where it actually belongs.
paul
6:54 a.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
Paul Koning wrote:
It's probably not a magnet, but rather a ferrite core. You'd know the
difference putting the pieces together -- if you feel no attraction or
repulsion, it's not a permanent magnet.
Interesting. The pieces do attract.
Are ferrite cores magnetic?
(I would think a ferrite core would have wires wrapped around it)
These magnets are not connected to the wired internal yoke assembly -
they are glued to a "collar" which is close to the back of the tube.
The collar is round but the magnets are glued to make a square - I
assume this helps make the image square. (or not :-)
The magnets on the two sides are symmetric as are the top and bottom.
Both top and sides have two "tube magnets" but ared spaced slightly
differently. The sides have two magnets side by side with no gap.
The top and bottom have two magnets side by side with a a 1/4" gap.
I can see where the glue was holding the magnet. That's where I put it
back.
I assume the poles should be aligned, i.e. the poles of the two magnets should
be the same, producing a larger overall field (I presume)
As for the problem, I wonder if the issue is that the
core is in the
wrong spot. It's part of the deflection magnetics assembly, and if
it's misplaced then you'd certainly get problems like you describe.
Take a look at the corresponding piece at the bottom of the yoke. I
would expect things to be symmetric. The fact that the thing fell out
suggests that it may have been out of position, and when you pushed it
back in you may not have gotten it back where it actually belongs.
Well, it fell out onto the floor when I took the enclosure off :-)
-brad
7:46 a.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
>>>> "Brad" == Brad Parker
<brad(a)heeltoe.com> writes:
Brad> Paul Koning wrote:
> It's probably not a magnet, but rather a
ferrite core. You'd know
> the difference putting the pieces together -- if you feel no
> attraction or repulsion, it's not a permanent magnet.
Brad> Interesting. The pieces do attract.
Brad> Are ferrite cores magnetic?
Nope.
Brad> (I would think a ferrite core would have wires wrapped around
Brad> it)
Not necessarily. I've seen deflection yokes that had ferrite in them,
but not with the wire around them.
Brad> These magnets are not connected to the wired internal yoke
Brad> assembly - they are glued to a "collar" which is close to the
Brad> back of the tube. The collar is round but the magnets are
Brad> glued to make a square - I assume this helps make the image
Brad> square. (or not :-)
Probably not... Anyway, sounds like it might be a focusing magnet.
Brad> The magnets on the two sides are symmetric as are the top and
Brad> bottom. Both top and sides have two "tube magnets" but ared
Brad> spaced slightly differently. The sides have two magnets side
Brad> by side with no gap. The top and bottom have two magnets side
Brad> by side with a a 1/4" gap.
Brad> I can see where the glue was holding the magnet. That's where
Brad> I put it back.
Brad> I assume the poles should be aligned, i.e. the poles of the two
Brad> magnets should be the same, producing a larger overall field (I
Brad> presume)
If the bore in the magnet is cylindrical, it would fit on the neck of
the tube two ways. Only one of those is right (and I'm not sure which
one that would be). So you might try taking it off and turning it 180
degrees to see if that improves matters.
Are you sure that the fragments are held together with no air gap? If
not you might try thin superglue to glue the pieces to fix that.
paul
8:09 a.m.
These are cylindrical, low-gauss ferrite magnets called 'trimming
magnets' or 'pincushion magnets'. A lot of cheaper CRT devices use 'em to
tweak the display. They're a pain in the butt, especially the ones near
the front of the CRT that gradually get demagnetized with each power-on
degauss cycle.
They are sometimes available at larger 'real' hardware stores (in the
US) like True Value, etc.
Or, as was wisely suggested, cannibalize them from another junk tube.
Chees
John
2:18 p.m.
New subject: Monitor deflection magnets;
It's probably not a magnet, but rather a ferrite
core. You'd know the
difference putting the pieces together -- if you feel no attraction or
repulsion, it's not a permanent magnet.
A ferrite core on its own probsbly wouldn't do much (unless it was
inserted inside a coil, say). It could be associated with a permanent
magnet, though.
As for the problem, I wonder if the issue is that the
core is in the
wrong spot. It's part of the deflection magnetics assembly, and if
it's misplaced then you'd certainly get problems like you describe.
Take a look at the corresponding piece at the bottom of the yoke. I
would expect things to be symmetric. The fact that the thing fell out
suggests that it may have been out of position, and when you pushed it
back in you may not have gotten it back where it actually belongs.
Another possibility is that there's something else -- say a permanent
magnet -- missing. Conpare the top and bottom of the yoke and if anything
is not theee. A permanent magnet, of course, might be stuck to any part
of the monitor chassis (and might be messing up the raster as a result!).
-tony
8:39 a.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
On Thu, 15 Jul 2004 10:09:47 -0400, Brad Parker <brad(a)heeltoe.com> wrote:
But - the "tube" has broken into 3 pieces
(it was broke when I found it.
honest). I carefully glued it back together (no glue in the joints,
however) and replaced it. This helped a little but did not cure the
problem.
A physical shock strong enough to break the magnet could easily have
also reordered the magnetic domains, causing it to become less
magnetic.
9:29 a.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
I also wanted to point out one thing (just to be clear/pedantic)
There are several (5-6?) small (like 1/4" x 1/2") magnets glued in
random places around the yoke collar.
These are not, however, the ones I'm talking about. I'm talking about the
ones that are "cylinder magnets" in the "mmm" places below. They are
all
about 2" long.
(hard to imagine why I would stoop to ascii art in this day of digital cameras)
viewed "through" the crt from the front:
-------------------
/ mmmmmmmmmmmmm \
/ mmmmmmmmmmmmm <------ this one fell out
|mm mm|
|mm mm|
|mm --- mm|
|mm / \ mm|
|mm \ / mm|
|mm --- mm|
|mm mm|
\ mmmmmmmmmmmmm /
\ mmmmmmmmmmmmm /
-------------------
Christopher McNabb wrote:
On Thu, 15 Jul 2004 10:09:47 -0400, Brad Parker
<brad(a)heeltoe.com> wrote:
But - the "tube" has broken into 3
pieces (it was broke when I found it.
honest). I carefully glued it back together (no glue in the joints,
however) and replaced it. This helped a little but did not cure the
problem.
A physical shock strong enough to break the magnet could easily have
also reordered the magnetic domains, causing it to become less
magnetic.
2:15 p.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
Hi,
I have an old B&W "specialty" monitor which recently stopped working.
In the process of moving it around (to/from repair place) I noticed a
little black "tube magnet" dropping out when I took the cover off.
At the time I didn't think much of it (those in the know can chuckle now).
There are few, if any, unimportant components in monitors :-)
So, after a bout of replacing bad caps with no luck, I eventually broke
down and replaced the deflection board and the monitor sprang to life.
Much joy.
(note: "specialty" = designed for a specific computer with a special ECL
What machine?
video connection and has no standard connector or
interface. and no
schematics)
No schematics is not an excuse for not repairing things properly. I've
had to start with no schematics quite often (and by the end of the repair
I normally have my own set of scheamtics...)
So, monitor is working. I proceed to adjust the H & V size, linearity, etc...
I notice that the bottom and sides will square up nicely but the top
edge has a large "dip" in the middle. No amount of trimmer fiddling will
fix this.
light goes off. "found" tube magnet is part of yoke assembly.
Quite probably...
So, I notice where the missing magnet came from. Naturally it's on the
top side of the yoke assembly.
But - the "tube" has broken into 3 pieces (it was broke when I found it.
honest). I carefully glued it back together (no glue in the joints,
What glue did you use? Isocyano acryliic hydro-copolymerising adhesive is
probably the bsst for this becuase it's such a thin layer. Did you
carefully align the broken parts (so no gaps) when you stuck them together?
however) and replaced it. This helped a little but
did not cure the
problem.
[note to reader: I never took that fields course. I know nothing of magnets.]
So,
- is a broken magnet pushed back together not as good as a whole magnet?
(strength wise)
Should be, provided there are no gaps.
- can I get a new magnet somewhere?
Is this a monochrome monitor? If so, try expserimenting with other small
magnets. I don't think you can do much permanent harm.
-tony
3:30 p.m.
New subject: Monitor deflection magnets; what to do when one falls out & breaks?
Tony Duell wrote:
A Symbolics Lisp Machine.
(note: "specialty" = designed for a specific computer with a special ECL
What machine? What glue did you use? Isocyano acryliic
hydro-copolymerising adhesive is
probably the bsst for this becuase it's such a thin layer. Did you
carefully align the broken parts (so no gaps) when you stuck them together?
I did. I didn't actually glue them - I just put a layer of silicone on
one side. I was careful to get it lined up (it had a nice glue strip which
made that easy)
Is this a monochrome monitor? If so, try expserimenting
with other small
magnets. I don't think you can do much permanent harm.
It's mono. I have a dead pc mono monitor downstair I plan to open up
and look for a replacement magnet :-)
-brad
7:23 p.m.
New subject: Monitor deflection magnets;
Tony Duell wrote:
A Symbolics Lisp Machine.
Very nice toy!
Is the monitor actually made by Symbolics, or is it a standard chassis
(e.g. Moniterm or somebody like that)?
-tony
(note: "specialty" = designed for a specific computer with a special ECL
What machine?
16 Jul
16 Jul
1:34 a.m.
New subject: Monitor deflection magnets;
Tony Duell wrote:
Is the monitor actually made by Symbolics, or is it a standard chassis
(e.g. Moniterm or somebody like that)?
It's made by Symbolics. Inside is a off-the-shelf p/s, off-the-shelf HV
supply, a custom deflection board, and a custom micro/interface board.
-brad
7383
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11 comments
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participants (5)
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ard＠p850ug1.demon.co.uk -
brad＠heeltoe.com -
cmcnabb＠gmail.com -
jpl15＠panix.com -
pkoning＠equallogic.com