Power Supply
Power A
Power B
Camera
Assembly
Primary
Power
Video Signal
Video Shield
Monitor
AC Voltmeter
- 9 -
(Ground Return)
Figure A Ground Loop
TROUBLESHOOTING
If you experience problems with the camera picture please check
these simple troubleshooting procedures for possible solutions before
calling technical support.
IMPORTANT NOTE: If you have removed the ground loop and
the horizontal line still remains on screen
call Videolarm technical support for further
information.
GROUND LOOPS
Generally a horizontal line on screen, whether moving or stationary,
means you have a ground loop problem. The video shield should
only be connected to ground through the monitor or other electronic
equipment that uses the video signal. Connecting the video shield to
ground at the camera will create a ground loop, which may interfere
with the video signal (See Figure A). This should not damage the
camera, but the video signal may become unusable. A ground loop
problem will cause a dark horizontal bar to slowly “scroll" through the
picture. To solve this problem, remove all ground connections from the
video connection EXCEPT for the ground at the terminating end of
the video signal.
The video termination should be a 75-ohm impedance, standard in
monitors and other video equipment. If the video signal goes to more
than one piece of equipment, a monitor and multiplexer input for
instance, insure that one and only one piece of equipment terminates
the video signal with 75 ohms; otherwise the image will be degraded
and may appear to be unusually dim.
STATIONARY OR SCROLLING HORIZONTAL
LINES ON SCREEN
AUTOMATIC BROWN OUT FEATURE
The camera includes an automatic brown out feature which is acti-
vated whenever the incoming voltage drops below 10 VAC or VDC.
LINE LOCK
All cameras are all shipped from the factory with the line lock function
disabled. If your application requires Line Lock contact Videolarm.
NVT TROUBLESHOOTING
If you are experiencing problems, attempt to simplify your setup. Test
each cable segment separately. For example, test the camera and
monitor together without the other equipment. Then add in the NVT
transceivers, back-to-back. Test each segment of a long cable-run
independently. Attempt to isolate the problem.
Below are problems that may be encountered. If the suggestions below
are not helpful, or the recommendations are not effective, please call
NVT’s customer support. NVT customer support can be reached 8:00
AM to 5:30 PM PST at (800) 959-9870 or at (+1) (650) 562-0600.
FAINT OR BLURRY PICTURE; LITTLE OR NO COLOR
Possible causes include:
1. Shielded twisted-pair cable. Verify that the wire is unshielded
twisted-pair cable. Multi-pair cable with an overall shield is OK.
2. Longer wire distance than expected. Be sure to include any coax
cable that’s part of this distance. Verify end-to-end connectivity
with an ohm meter. Measure the distance by disconnecting the
transceivers, shorting the far end, reading the loop’s resistance
at the near end. See above for ohm vs. distance ratings. If
necessary, replace transceivers with correct models specified for
this distance.
3. Incorrect distance equalization setting. Adjust the equalization
controls) with a mini screwdriver (NV-652R, NV-862R or the NV-
1662R). If the transmitter is an NV-653T, verify correct equalization
switch setting.
4. Poor connection at a punch-block, splice, or coax cable. Re-check
using the method described in #2 above, or use a wire test set.
5. Short between conductors of the twisted-pair. Use an ohm meter to
locate the short.
6. Transient protection devices employing metal-oxide varistors. Use
carbon blocks, gas-discharge tubes, or NVT transceivers w
i
th built-
in protection.
7. Check the camera. Are the focus and iris set correctly? Verify with
portable monitor.
EXTREMELY FAINT PICTURE
Only faint shadows of the original picture are visible. One of the
twisted pair conductors is open or the wires are shorted together.
Check with an ohm meter.
OVER-SATURATED COLORS; HIGH CONTRAST GRAINY
PICTURE; TOO BRIGHT, TORN PICTURE
Adjust the distance equalization as necessary. Verify that the monitor
has a 75 termination, not in “loop-through”.
WON'T SYNC; WIDE, WHITE JAGGED AREAS
Looks like a scrambled Cable TV signal. Check polarity.
WON'T SYNC; TORN PICTURE
1. Make sure that you are using unshielded twisted pair wire.
2. Check distance equalization settings.
3. For installations with passive (non-amplified) transceivers at both
ends, check for ground loops. This may be done with an AC
Voltmeter, as shown below:
