Chapter 2

CHAPTER 2: SERVICE / INSTALL

Audio Carriers Video Carriers Digital Carriers Signal Problems Line Issues Cable Damage Grounding Issues Electrical/Mechancil Ground Problems Splitter Problems Ingress Ghosting Signal Leak Problems Picture Distortions Negative Trap Problems Positive Trap Problems Tiling House Amps Remote Problems Box Issues DCT Diagnostic Codes LED Error Codes

1. Remember, the return path is very important for successful working digital services, ie VOD, IPPV, High speed Internet, VOIP

2. Taking levels throughout your troubleshooting can speed up your search for a problem

3. Look for the most obvious solution but don't assume what the problem will be before you get there and don't look for only one solution, be open to the possibility of anything causing a problem

4. Analog problems should be cleared up first because they may also clear up digital problems in the process.

5. Don't be afraid to ask for help if you get stuck, your co-workers are here to assist you; we're all a team.

6. Steps of troubleshooting
      Identify
      Analyze
      Locate
      Diagnose
      Repair
      Testing

VIDEO CARRIERS

No less than 0 dBmV

No more than 3 dB difference for adjacent video carriers

No more than a 10 dB difference between lowest and highest signal levels in the system

HRC=Harmonic related carrier

Over the air ingress on HRC freqs don't appear as ghost because HRC freqs are shifted by 1.25MHz

Because OTA is 1.25MHz above HRC, ingress shows up as distorted diagonal lines

IRC=Incrementally related carrier

Black and white analog channels but color on digital, check STD, HRC, IRC

AUDIO CARRIERS

Must be 10 to 17 dB below video carrier on the same channel

Center frequency must be 4.5 MHz above video carrier

DIGITAL CARRIERS

Should be 6 to 10 dB below adjacent analog levels

MOST SIGNAL PROBLEMS STEM FROM

Poorly installed fittings

Shorted Center conductors

Smashed, cut or faulty cable

Faulty splitters

Faulty traps

LINE ISSUES

Snow is due to noise and appears when signal is too low

RF low = snow

RF high = cross modulation

Cross threaded = Level fluctuation, ingress/egress, flashing picture

Black center conductor = water damage

Water damage could cause a 4 dB decrease at 450 MHZ and no change at 55 MHz

EXAMPLES OF CABLE DAMAGE

Staples or nails through cable

Animal chew

Scrapes

Violation of bend radius

Water damage

GROUNDING ISSUES

Snowy picture on 23 and up

Snowy picture on all channels

High ground resistance (> 25 ohms)

ELECTRICAL AND MECHANICAL GROUNDING PROBLEMS

Electrolytic corrosion

Broken ground wire

Paint

SPLITTER PROBLEMS

Snowy pictures

Ingress/egress

Barker channel response

Distorted FM reception

Clear picture on 1 channel, snow on another (backward installed splitter)

RETURN PATH PROBLEMS

Forward band pass of 54-600 MHz could block return path signal

VCR before Box

Defective or wrong house amp

High return (+52)

Loose/improperly installed fitting

" Push-on" jumper

Too many TVs

Loop through system

Wire damage

Ingress on only 1 set means that leak is between splitter output and set

Ingress on all, problem is prior to main splitter

If ingress is back feeding, it usually stems from the TV with the worst picture

   One test to locate if problem is interior or exterior
      Disconnect line at ground block
      Check channels 2,4, and 7; if picture is present then the problem is in the house
      If the picture is snowy then the problem is between the ground block and the tap or a line       problem

Another is using reverse ingress
Hook up meter to line back toward the disconnect drop to see if you read anything, shouldn't see any level above neg. 40 dBmV

Causes high BER

As the difference in amplitude between the 2 video carrier signals levels approach 0, the ingress will appear more severe

   Ghosting types
      Leading (Left of desired picture)
      Trailing (Right of desired picture)

SIGNAL LEAK PROBLEMS

Scraped, cut, stapled, chewed cable

Wrong sized connector, loose connector and corroded fittings

Broken/corroded passive devices

Loose amp housing bolt

FAA concerns itself with leaks in the freq band 108-137 and 225-400 MHz

To check the drop, remove drop from ground block and install an F-81 barrel and 75 ohm Terminator, recheck

PICTURE DISTORTIONS

Electrical interference
White dashed lines

Double Images
2 unrelated images on the same frequency

Phase Locked
Dark vertical bar

      Co-Channel
         Appear as shimmering dark and light horizontal bars
         If in headend, is only on 1 channel; if in the field, is on all channels

      Cross modulations
         Caused by the transfer or crossing of modulation from an undesired channel to the desired          channel within a damaged misadjusted or improperly fed amp
         Results are a weak reproduction of undesired channel superimposed onto a desired picture
         The interfering picture moves back and forth across the screen and displays a vertical and          horizontal bar

      Hum Modulation
         The amplitude of broadband cable video and audio carrier by 60 or 120 Hz AC voltage
                  Visible by 1 (60 Hz) or 2 (120 Hz) bars
                  Moving bars are most common
                  If visible, then probably audio
                  Can't be detected by SLM w/modulated Video carrier because hum modulation is masked                   by the video modulation

      Beats
         Diagonal
         Horizontal
         Herringbone (zigzag)
         S curved beats

Flashing
Horizontal white streaks varying in size

      Intermodulation
         One or more beats caused by 2 or more RF carriers mixing together within an active device          operating outside its design parameter
         This causes
                  Near vertical lines that move from left to right and cover about 10% of the screen
                  Diagonal lines that more from left to right
                  Narrow lines in a herringbone pattern
                  S-curved lines
         These beats are never part of the picture
         The higher the amplitude of the beat, the more severe the appearance of the distortion

NEGATIVE TRAP PROBLEMS

Partial or normal viewing of trapped channel

Poor audio on lower adjacent channel

Snow on all channels

Ingress

POSITIVE TRAP PROBLEMS

Herringbone beat and warble audio tone

Snow on all channels

Soft or blurry picture of trapped channel

Ingress

   Low input due to
         Loose fittings
         Too many TVs hooked up
         Cut in the drop cable
         Backward installed splitter
         Low levels from the tap

Ingress

Adding an amp to negative digital levels will only amplify crap

Passive return amps will add either 7 or 15 to the return path

Active return amps will deduct either 7 or 15 to the return path,

Amps are best used in homes with several TVs and/or long cable runs inside the house

Amp a modem line only if completely necessary

REMOTE PROBLEMS

Bad line of sight

Defective Box

Weak or dead batteries

Unprogrammed remote

Defective remote

Flip bar with no picture

Not active (disconnected)

VCR before DCT

Backward splitter

No picture; must go to list and start a recorded program, once you return picture has returned
this is a bad box

Picture will freeze until you channel up or down, bad box

1989 recordings, NEVER try to delete, swap box

"8888" Electrical surge

"0" on a DCT is a return path problem

Box will turn itself on and off

Unable to record or pull up list

DCT DIAGNOSTIC CODES

D01	General status of DCT
D02	Out of band status, SNR
D03	In band status, SNR, MOD mode and tuned Freq
D04	Audio/Video status
D05	Unit address (will display on front LED)
D06	Firmware version
D07	Current channel status, Ch + Freq
D08	Renewable Security
D09	Upstream modem, IPPV status
D10	Application code mode
D11	Memory configuration
D12	Interactive info
D13	MAC Freq table
D14	Message table
D15	In-band PAT
D16	In-band PMT
D17	Task status
D18	IB MCA status
D19	Keyboard LED

LED ERROR CODES

E00	No error
E01	Not connected
E02-7	Nothing
E08	Post error (send to repair)
E09	NVRAM corrupt (send to repair)
E10	Nothing
E11	invalid unit address (send to repair)
E12	Nothing

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