Sony GDM-F520 Monitor - Strange Blur Problem

[Scrim]

Hi,
I picked up a used Sony GDM-F520 monitor recently. Most of the time it's
fine, but I get a problem just after it's switched on, if it's been off for
a while.
After a short delay it goes very blurry. If I switch the monitor off/on the
fault clears (so long as I wait a moment after switching off for the
internal relay to click before I switch on again. If I do the off/on quicker
than this, it doesn't help).
This repeats 2 to 4 times over the initial 10 minute or so of warm up, and
then goes away.
I'm think the blur is entirely in the horizontal direction.
I'm hoping the solution is straight forward as I don't have any experience
with monitors/TV's etc.
I do have a copy of the service manual with schematics though.
Any help would be very much appreciated as this is otherwise a really great
monitor!
Thanks,
Scrim

 

[Mr. Land]

I'm think the blur is entirely in the horizontal direction.

Can you clarify this? For instance if you were looking at a single,
lowercase, black 'o' character on a white background at the center of
the screen when the blur problem is happening, which part(s) of the 'o'
would be blurry? Just the left and right sides and not the top and
bottom?

 

[Jerry G.]

In these, usually it is the HV multiplier, or the CRT is failing. In
most cases it was the HV miltiplier.


Jerry G.

--

 

[Scrim]

Can you clarify this? For instance if you were looking at a single,
lowercase, black 'o' character on a white background at the center of
the screen when the blur problem is happening, which part(s) of the 'o'
would be blurry? Just the left and right sides and not the top and
bottom?

Yes, Just the left and right sides of a letter O would blur. The effect is
the same at all points on the screen, edges, middle, the lot.
In fact I've seen it happen with a square: the horizontal lines are
practically unaffected, but the vertical lines are completely blurred.
I have photos.

Scrim

 

[Andy Cuffe]

In these, usually it is the HV multiplier, or the CRT is failing. In
most cases it was the HV miltiplier.


Jerry G.

I've seen a lot of recent Sony monitors with bad CRTs that cause
intermittent focus problems. Sometimes they seem to get better, other
times they become unusable. I'd keep using it as long as possible,
but keep an eye out for a new monitor.
Andy Cuffe

[email protected]

 

[Scrim]

In these, usually it is the HV multiplier, or the CRT is failing. In
most cases it was the HV miltiplier.


Jerry G.

I'm no expert on monitors, but wouldn't an HT problem cause an equal loss of
focus in all directions, instead of what I'm getting, which is a loss of
focus, or blurring of some kind, only in the horizontal direction?
To me it looks as I'd imagine it would if a very high frequency sine wave
was modulating the horizontal deflection voltage by a few percent. Or if
these things have independent horizontal and vertical focus (I can't imagine
how???), then I'd suspect the horizontal focus circuit had an intermittent
fault.
Thanks,
Scrim

 

[Scrim]

I've seen a lot of recent Sony monitors with bad CRTs that cause
intermittent focus problems. Sometimes they seem to get better, other
times they become unusable. I'd keep using it as long as possible,
but keep an eye out for a new monitor.
Andy Cuffe

[email protected]

Hi,
What kind of tube problem would cause an intermittent blurring in only the
horizontal plane?
Isn't this most likely an intermittent fault somewhere in the electronics?
Scrim

 

[Mr. Land]

I agree. I don't see how a HV or focus voltage problem would mess up
the focus in only one direction (unless it's some strange interaction
with one of Sony's non-standard shadow masks or something like that,
but that seems unlikely.)

It seems more likely that, if you are somehow losing your video
bandwidth you'd get blurring like this. Something in the video
circuitry could be intermittently limiting bandwidth, so when the fault
is occuring and the electron beam in the tube is about to draw one of
the lines making up the "o" in my example, instead of the video level
jumping "instantaneously" from white to black (which requires good
bandwidth) at the edge of the "o", it rather ramps down to black. So
what you see is a fade (aka blur) from white to black instead of a
nice, sharp, crisp line.

If I've convinced you of this hypothesis, I also have some land for
sale....

 

[Scrim]

I agree. I don't see how a HV or focus voltage problem would mess up
the focus in only one direction (unless it's some strange interaction
with one of Sony's non-standard shadow masks or something like that,
but that seems unlikely.)

It seems more likely that, if you are somehow losing your video
bandwidth you'd get blurring like this. Something in the video
circuitry could be intermittently limiting bandwidth, so when the fault
is occuring and the electron beam in the tube is about to draw one of
the lines making up the "o" in my example, instead of the video level
jumping "instantaneously" from white to black (which requires good
bandwidth) at the edge of the "o", it rather ramps down to black. So
what you see is a fade (aka blur) from white to black instead of a
nice, sharp, crisp line.

If I've convinced you of this hypothesis, I also have some land for
sale....

Loss of bandwidth! Yes, that would do it! Thank you - new theory. It makes a
lot more sense than my mystery high frequency modulation (which would
require lots of spare bandwidth, so didn't sound likely).
The only other possibility I can think of is if they do have separate
horizontal and vertical focus (cylindrical electron lenses?) - it's just
that I vaguely recollect reading that they do. Anyone know about that?
New:
I just got hold of "Nokia Monitor Test" and checked to see if the effect
varies with the screen resolution set in windows, and it doesn't as far as I
can tell - the physical width of blurring remains fairly constant - but I
think I now have to admit that there is some blurring in the vertical
direction too, although it's not as bad. I guess that points back to the HT?
This morning also, for the first time, I left the screen blurred to let it
warm up. Just as I returned I heard a small 'pop', which coincided with the
screen image momentarily collapsing.
So perhaps the horizontal/vertical variation in blurring is just a
consequence of the aperture grill and there is some kind of HT problem where
charge is building up and that's causing the blur?
I'll leave it blurred and watch it like a hawk tomorrow morning.
Scrim

 

[Andy Cuffe]

Hi,
What kind of tube problem would cause an intermittent blurring in only the
horizontal plane?
Isn't this most likely an intermittent fault somewhere in the electronics?
Scrim

There's a large HV resistor in the electron gun which can fail. This
causes all sorts of strange problems. I saw one that was physically
cracked once. It would go out of focus and snap back into focus.
It's also possible for arcing, or leakage around the focus grids to
cause intermittent focus. These CRTs use separate horizontal and
vertical focusing grids, so it's not unusual for them to go out of
focus in one direction only.
Andy Cuffe

[email protected]

 

[Andy Cuffe]

The only other possibility I can think of is if they do have separate
horizontal and vertical focus

They do in fact have separate horizontal and vertical focus. The two
interact slightly, so if it goes out of horizontal focus, the vertical
focus will also be affected.

I had a 21" Sony with a CRT that would intermittently go way out of
focus in the horizontal direction. Sometimes it was unusable, but it
often went for weeks without a problem. Normally it would only snap
out of focus for a second or two every few days. I eventually
replaced the CRT with one from a scrap monitor and it's been working
fine for a couple of years.
Andy Cuffe

[email protected]

 

[Scrim]

They do in fact have separate horizontal and vertical focus. The two
interact slightly, so if it goes out of horizontal focus, the vertical
focus will also be affected.

I had a 21" Sony with a CRT that would intermittently go way out of
focus in the horizontal direction. Sometimes it was unusable, but it
often went for weeks without a problem. Normally it would only snap
out of focus for a second or two every few days. I eventually
replaced the CRT with one from a scrap monitor and it's been working
fine for a couple of years.
Andy Cuffe

[email protected]

Hi Andy,
It sounds like I'll have to reluctantly accept the problem might be the
tube, but take a look at the HV multiplier area first.
In the GDM-F520 Service Manual (page 3-5) is a diagram showing the "FBT"
with two knobs marked "Focus 1" & "Focus 2". Is that one each for Horizontal
& Vertical focus? If so , I wouldn't mind betting that the pot track contact
is playing up. If not, are there pots elsewhere?
I'm really keen to keep this monitor running for a few year, not just to get
my monies worth (important), but because I doubt I'll replace it with
anything as good! It's only thanks to everyone changing over to panel
screens that the opportunity to own a top of the range monitor like this has
come my way.Thank you progress! It's ironic that it turns out the top of the
range monitor has serious design flaws! Sony! Hang your heads in shame! Dig
out your Samurai Swords, or apologise and do your best to remedy the
situation (with information if nothing else)!
Scrim

 

[Andy Cuffe]

In the GDM-F520 Service Manual (page 3-5) is a diagram showing the "FBT"
with two knobs marked "Focus 1" & "Focus 2". Is that one each for Horizontal
& Vertical focus? If so , I wouldn't mind betting that the pot track contact
is playing up. If not, are there pots elsewhere?
I'm really keen to keep this monitor running for a few year, not just to get
my monies worth (important), but because I doubt I'll replace it with
anything as good! It's only thanks to everyone changing over to panel
screens that the opportunity to own a top of the range monitor like this has
come my way.Thank you progress! It's ironic that it turns out the top of the
range monitor has serious design flaws! Sony! Hang your heads in shame! Dig
out your Samurai Swords, or apologise and do your best to remedy the
situation (with information if nothing else)!
Scrim

Yes, those are the horizontal and vertical focus knobs. One affects
both almost equally and the other mostly affects the horizontal. It's
worth running both controls through their entire adjustment range a
few times just in case it is a dirty pot or something.

Display a pattern of white vertical lines and adjust the horizontal
for the thinnest vertical lines. Don't forget to look at the extreme
right and left edges because a small misadjustment can make the edges
extremely blurry. The correct setting will be a compromise between
the edges and center. Next display some thin horizontal lines and
adjust the vertical focus for the thinnest horizontal lines. Also be
sure the check the top and bottom focus as well as the center. Go
between them a few times and finish on the vertical focus so the
raster lines are as sharp as possible. That's not the official
adjustment procedure, but I've found it produces the best results.

These are very nice monitors, but they have their share of problems.
The other common problem is that the brightness tends to increase as
the CRT ages. Eventually it gets so bright that it can't produce
black at all. The official fix is to use the alignment software to do
a complete grayscale adjustment. This requires software and
equipment not available to most people. There is a resistor that can
be changed to reduce the G2 voltage. Later models could correct this
problem using the color return feature, but I don't think the F520
can.
Andy Cuffe

[email protected]

 

[Scrim]

Yes, those are the horizontal and vertical focus knobs. One affects
both almost equally and the other mostly affects the horizontal. It's
worth running both controls through their entire adjustment range a
few times just in case it is a dirty pot or something.

Display a pattern of white vertical lines and adjust the horizontal
for the thinnest vertical lines. Don't forget to look at the extreme
right and left edges because a small misadjustment can make the edges
extremely blurry. The correct setting will be a compromise between
the edges and center. Next display some thin horizontal lines and
adjust the vertical focus for the thinnest horizontal lines. Also be
sure the check the top and bottom focus as well as the center. Go
between them a few times and finish on the vertical focus so the
raster lines are as sharp as possible. That's not the official
adjustment procedure, but I've found it produces the best results.

These are very nice monitors, but they have their share of problems.
The other common problem is that the brightness tends to increase as
the CRT ages. Eventually it gets so bright that it can't produce
black at all. The official fix is to use the alignment software to do
a complete grayscale adjustment. This requires software and
equipment not available to most people. There is a resistor that can
be changed to reduce the G2 voltage. Later models could correct this
problem using the color return feature, but I don't think the F520
can.
Andy Cuffe

[email protected]

Thanks Andy, that's very helpful.
My F520 has "Image Restoration", which I think must be the "color return
feature" you describe?
The User Manual has this to say about it:
-----------------------------
To restore the color from the EASY, PRESET, or sRGB modes ( IMAGE
RESTORATION):
You can restore the color to the original factory quality levels. Before
using this feature, the monitor must have been in normal operation mode
(green power indicator on) for at least 30 minutes. You may need to adjust
your computer's power saving settings. If the monitor has not been on for at
least 30 minutes, the "AVAILABLE AFTER WARM UP" message will appear. Also,
this function may gradually lose its effectiveness due to the natural aging
of the Trinitron picture tube.

 

[Andy Cuffe]

Thanks Andy, that's very helpful.
My F520 has "Image Restoration", which I think must be the "color return
feature" you describe?

That's the feature I'm thinking of, but for some reason it doesn't
work (well) on a lot of the 21" monitors. For some reason it works
fine on the same age 19" monitors. They fixed it on the later 21",
bit I think the F520 was made before they fixed it.

If it works it really will restore the correct brightness and
grayscale. I've seen monitors that were so far out of adjustment that
they were scrapped. Simply running the image restore made them look
like new.
Andy Cuffe

[email protected]