Olson Technology OTD-3000 - Manual (Page 11)

025-000053 REV G Page 11
OTD-3000
TROUBLESHOOTING ADDENDUM
Troubleshooting:
1) This unit has a restricted AFC range. This is done to eliminate a problem inherent in many low cost modulators
incorporating AFC. That problem occurs when the desired off-air channel goes off the air and the AFC has a
wide enough range to pull in an adjacent channel. In most cases the AFC holds the undesired channel when the
desired channel returns to the air.
2) However, many independent UHF broadcast stations and translators operate out of specification with regard
to F.C.C. rules. We have found some in excess of 1MHz from their specified channel allocations. Fortunately
your demodulator is capable of selecting the L.O. frequency in 0.25MHz increments. This will allow you to
select an L.O. frequency to compensate for your UHF station error.
3) Make sure that the DIP switches for Channel Select are in the correct position according to the channel select
chart. Ensure that the Band Select Switches are in the proper position. Put the AFC switch in the “Off” or up
position.
If you hear audio but no video is present, your input level to the UHF input is either too low (-20dBmV or
below) which triggers an internal squelch circuit or the UHF transmitter may be off frequency. An off frequency
input will cause the unit to act like a low level input signal because it will run the video carrier down the rejection
slope of the IF SAW filter.
If a field strength meter is available, measure the UHF input level for the channel of interest. If it is below
-10dBmV, a preamplifier is recommended. If possible, view the UHF signal on a TV set and ensure that you
have an adequate picture. If properly set-up, the OTD-3000 should produce a picture of comparable video
quality.
View the video output on a suitable composite video monitor. If it is of comparable quality to the off-air
signal, the unit and the TV station are both operating properly.
If the picture is of inferior quality or there is no picture, begin changing the L.O. frequency by the following
procedure:
1) The first two DIP switches as viewed from left to right are always in the down position and the third
switch is always in the up position for standard frequency allocations.
2) Moving the first switch to the UP position will increase the L.O. by 0.25MHz. If the picture improves
significantly, move the 2nd DIP switch to the UP position, and the first switch back to the DOWN position.
This increases the L.O. by 0.50MHz. If the picture quality is not as good as with 0.25MHz offset, return to
the 0.25 offset position (lst switch UP) and activate the AFC switch (DOWN position).