Star Tech Journal

STAR*TECH Journal
Mey 1987
Determining Sync Polarity
With A Voltmeter
By
If two sync wires are provided from the
logic board, it can be thought that
separate vertical and horizontal signals
are supplied. If there's only one wire
given, assurre COJOIX)site sync is supplied.
Sam Cross
Godwin Distributing Co.
North Little Rock, Arkansas
In hooking up a logic board it is
essential that the correct sync signals
get to the oonitor to lock the picture in
place. Here is a listing of sync signals
starting from the oost co11100nly used to
the least co11100nly used.
1) Negative coJaIX)site sync - this signal
consists of the vertical and horizontal
sync signals mixed together.
2) Positive composite sync - vertical and
horizontal signals mixed together.
e
3) Separate positive vertical and
horizontal - two separate lines, one for
vertical sync and the other for horizontal
sync.
4) Separate negative vertical and
horizontal - two separate lines for each
sync signal.
Both postive and negative sync signals are
above ground signals. Positive gets it
name from the signal normally at ground
(inactive) and the sync pulse going to
+SVOC when active. Negative sync is
normally at +SVOC (inactive) and dropping
to zero volts when active.
0
~
~j\\/E:"o~
l{oRl'I\F\U,',{
Ai
ill
~
~\/ES~
"'~~~~
~---~~
~~) ' ~ .o-+s
~~"-l~
..,~ F\Ci\\JE:
[7)
()
Since negative sync is normally at +SVOC
and dropping to ground when active, it's
going to read a higher voltage than
positive sync, which is a normally zero
voltage which goes to +SVOC when active.
Here are the readings taken with a digital
neter.
?®ATIVE
POSITIVE
Composite Sync
4.20V
67.BMV
Vertical Sync
2.48V
156.6MV
Horitzontal Sync
2.44V
90.BMV
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