BTW i have a LCD monitor exhibiting the equivalent of burn in now.
There was an interesting thread in comp.ibm.hardware.chips about the
'LCD" 'burn in' or storage effect, depending on the system and
manufacturer it sometimes helps to display white for say a night.
I saw line burn in on a scope only once, and only heard reports of it on
TV's.
First a correction, I think the tube was DG7-32
http://members.chello.nl/~h.dijkstra19/page3.html
It is the small one next to the big radar tube.....
This was my first oscilloscope 'design' (well I designed the power
supply), it was a tube oscilloscope, probably 1MHz bandwidth, no trigger,
just 'sync'. A year later I designed a transistor one, with video output
transistors in the deflection, real trigger, double timebase, on a printed
ciruit with RTL logic! But anyways, this DG7-32 burned in in the first
hour or so...
^equalization
See below.
No, it has to do with maintaining h-sync.
Eh, yes and no.
In the olden days the time constant in the H PLL was really big, so the
set would just carry on at last freq if bad signal.
Then VHS came, and it had big timing errors in H due to the head position
changes, a big jump in H at the end of the frame (and missing lines at the
head switch-over).
So then sets got a much shorter timeconstant for H.
There was a time TV sets had 2 time constants.
Equalization pulses bent the H sync so that it would be back in place at
the
end of V sync. They occur on blank lines both before and after the V
sync series.
Yes I know where they are.
Let's go a bit deeper:
If you xor the H with a longer V you get reversed H, but now the H starts
posive, and trhe differentiator in the sync separator deleivers a
negatibve pulse, and as we were using the negative pulse it is about 4.7uS
late. However the H PLL will adjust in few lines.
-- ------------ ------------ --
| | | | | | |
| | | | | | |
-- -- ------------- ---
|| ||
|| ||
|| ||
position of 'optional' egalisation pulses.
This system was designed so you could just with a simple differentiator
and integrator split the composite sync.
.
.
integrator .
neg polarity R . ramp build up
during v sync. comp sync ----------====-------------- V sync .
| |
| === C
| |
| ///
| |\
| differentiator | \
| | | C ___ __| \_____
-----| |---------------- H sync | /
| | | | /
| |/
[ ] R This edge is used (_also_
[ in egalisation pulses!)
|
///
It must again be stressed that the comp sync does not need any
egalisation pulses if the display is not interlaced.
maybe some of you will remember the real start of computing, Motorola
max-board with 6845 CRT controller, you just made comp sync by xoring a
H pulse with a V pulse....... And the TV would be nicely locked.
And that twas even a common clock.
You forget it only displayed on even fields. It was not until the 6845A
that you could even try to use both vertical scans and even then it did
not work correctly.
Actually in the above drawing the V ramp is negative of course.....
I would have to climb in the attic, but I had interlace on a Z80 system
I designed with a 6845, but not sure it was 'A' or not.
Interlace is just a phase relationship between H and V, if you have a
Lissajous (spelling) display of 2 sine waves on the scope, you can phase
adjust so the lines do not overlap (pairing it is called).
The extra pulses cause the V integrator cap to charge a bit different, and
change the phase where the V triggers.
That is what was in my TV study book (no idea who wrote it, but it was
good).
I think the H frequency does not _normally_ 'jump' during V sync (as in
VHS). It is just a matter of phase of V.
You can generate a 15 kHz sawtooth, and scope it.
Put the scope on a 20 ms trace, then you can change scope ms / division so
you see overlapping periods, or the sawtooth periods next to each other.
In one case you see 312.5 in the other 625 periods.
Is this right?
I think I tried this once, but maybe getting a bit rusty in this.
What do you think?
I haven't said it would work, but it does not meet specification. It was
a real PITA to meet spec in the tube days.
Well, I worked in the TV studio as engineer in the sixties, the old
sync generator had toobes, and very complicated, toobe flip flops....
yes it was full spec.... and a man height cabinet with forces air cooling.
When color came (1967 here) we got nice transistor sync generators....
All this interlock color carrier, 25 Hz offset, 8 frame editing sequence
for PAL, quadruplex.. amtec colortec color corrections....
But fact remains that you get color too with a 4,43MHz unlocked oscillator
(like in video games).
Just the interference pattern in the color areas then moves randomly on a
BW set..... But the sets (old and new) would eat almost anything you threw
at it.
