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UNIDEN
Uniden UST-7007
The following information is taken from "The Repair
Manual edition 4" by Martin Pickering ISBN 0-946273-12X
Note: When working on main PCB, always disconnect the plug
from the power supply board. The high voltage stored in the
smoothing capacitor is easily shorted to the 5 volt line and
will destroy the microprocessor.
Blows main fuse:
See end of UST-8008 section.
Frequency tunes in large steps. Unable to fine tune
some channels:
DBS has been selected instead of ECS. Press "DBS" button
until display reads "ECS" then press MEMO button. Do this
for every affected channel. (With DBS selected, frequency
steps are ~ 4MHz. For ECS, frequency goes in 1MHz
steps).
No LNB voltage:
Check switch setting on rear panel. Left position is 0 volt.
Centre is 18 volts. Right is 15v for ECS and 18v for
DBS.
Check Voltages from transformer secondary on J401.
Check fuses F401 and F402.
Check bridge rectifier behind F401.
Ensure voltage is reaching IC115 with 12 volts coming out.
(IC115 is in the centre of the panel, adjacent to the right
of the mains transformer.
Check voltages on Q112, Q145 and IC116 (near the rear panel
switch).
Panel display shows stars:
Microprocessor IC113 may have died (unavailable).
No tuning voltage or no variation in tuning
voltage:
Check C108, C109, C111 and IC102.
Intermittent picture or intermittent
sound:
Dry joints on Scart socket, R.F. modulator or relays.
Intermittent dead:
Dry joints on power supply connector.
Destroys LNB:
Intermittent shorted turns on mains transformer primary.
Intermittent patterning:
Replace modulator.
Poor pictures:
Replace capacitors inside tuner.
Videocrypt decoder does not work:
An internal modification is possible to allow the decoder to
work (see photograph). The resistor can be 1k to 10k in
value. Cut the track each side of the capacitor connection,
as indicated by arrows. The TV must be connected to the RF
output socket because the decoded picture is not routed via
the TV SCART. Connect the decoder to the VCR Scart
socket.
1. Undo the four black cross-head screws and remove the top
cover.
2. Undo the four chrome cross-head screws and remove the
bottom plate.
3. Locate IC127 which has a spare section that we will
use.
4. Use the picture to identify the track to be cut. Cut the
track on each side of the 100uF capacitor.
5. Join the two cut ends of the track, leaving the 100uF
capacitor unconnected.
6. Solder a wire from the free "+" end of the 100uF
capacitor to pin 4 of IC127.
7. Solder a wire from pin 5 of IC127 to the position marked
"Q135".
8. Solder a wire from pin 3 of IC127 to pin 20 of Scart 2
(J114).
9. Solder a wire from pin 9 of IC127 to the position shown
in the picture.
10. Solder a 10k resistor between pins 8 and 5 of Scart 2
(J114).
11. Check all connections for position and soldering
quality.
12. Replace base plate and cover.
13. Connect receiver and switch on.
14. Tune in a Videocrypt encoded channel.
15. Connect a Videocrypt decoder to Scart 2 (J114).
16. The unit should automatically feed the signal through
the decoder.
17. If a picture is not present then IC127 (4053) may be
damaged.
If the UST-92 D2MAC transcoder is connected, the TV must be
connected to the UST-92 TV SCART socket (or RF socket on
later models) because the D2MAC picture is not routed to the
receiver TV SCART or to the RF output. You must select
[MAC] on the receiver front panel button.
Note: When working on main PCB, always disconnect the plug
from the power supply board. The high voltage stored in the
smoothing capacitor is easily shorted to the 5 volt line and
will destroy the microprocessor.
Uniden UST-8008
No polariser output:
Q801 tends to overheat. Sometimes it goes short circuit and
sometimes it melts the solder and falls out. I always
replace it with a BD936 or TIP32A on the upper (track) side
of the PCB as shown in the sketch. Fit double-sided foam
adhesive tape beneath transistor.
Polariser skew insufficient:
Replace one of the two large resistors (100 ) with 47 0.5W
(R828 or R834). You can check the polariser current by
fitting a 68 2 Watt resistor to the polariser terminals on
the rear panel. Adjusting the skew to maximum should give a
reading of at least 8 volts across the resistor.
No LNB voltage with 15V selected by
switch:
Replace fuse F401 (T1A) with T2A fuse. If still no LNB
voltage, check inside the tuner; the track breaks where the
"F" connector is soldered. If T2A fuse melts the mains
transformer may have an intermittent fault.
14/18v modification
 Disconnect
the power supply from the main board.
Locate pin 7 of IC804 on polariser board. Solder a wire to
it and feed the wire through the main board to the
underside.
Remove the 7815 regulator (the front one of three on the
aluminium divider wall) and refit it with an insulating kit.
Do not resolder the centre leg.
 Fit
transistor, 3v9 zener and resistors as shown. Connect the
wire to the 3k3 resistor. Connect power supply. Select +++
for 14v and - - - for 18v.
No tuning voltage:
Check D405 (27 volt zener).
No voltage from transformer:
Replace transformer.
Low video gain. Poor, unlocked
pictures:
Replace 10 F capacitor inside the tuner (front right
side).
Test this by warming the capacitor with a soldering
iron.
Tuning problems:
Check C106, C107, C108.
Blows main fuse:
Remove and discard the large capacitor which is close to the
fuse.
If the fuse still blows, renew the transformer.
Using External decoder
Connect decoder to the right hand SCART socket as viewed
from front. Open flap and press [AUX] until you see
[A1] indicated. Press [MEMO]. Repeat for
each scrambled channel.
UNIDEN UST-771 Positioner
No drive East or West:
Most faults are caused by incorrect installation.
Replace Q109 even if it measures correctly.
Check Q110, Q105 and Q106 for short circuit.
Check cut-out which goes open circuit.
Check D120, D121, D119 which go short circuit.
Check Opto couplers IC108 and IC109 which go open
circuit.
Loses memory:
Measure battery cell on the main board. When new this is 3.2
volts. Causes problem if less than 2.8 volts. Replace if
less than 3 volts. Cut tags of existing cell, leaving them
as long as possible. Solder tags of new battery to tags
still in board. Saves the trouble of taking out the board
and also allows the largest size of cell to be fitted for
longer life. Battery available from SatCure.
Loses memory after mains failure:
On early versions, remove the wire link between R164 and pin
33 (end pin) of the microprocessor.
On later versions, cut the track which forms the same
connection.
UNIDEN UST-92 D2Mac decoder
The UST-92 is designed to work with Uniden receivers.
Although it may work satisfactorily with other makes of
receiver, consistent operation can not be guaranteed. In
particular, it will not work correctly unless the receiver
has the correct MAC de-emphasised baseband output
available.
The UST-92 will usually not work with Pace or Monterey
receivers.
Note: Later UST-92 decoders include Eurocrypt. Of the
earlier types, only those of "series 7" can be modified to
incorporate Eurocrypt.
Note: Eprom versions prior to v5.03 may not support Filmnet
encryption reliably.
(The Eprom must be a fast access, 120nS, type 27C512).
Upgrading the UST-92
Disconnect the mains supply and remove the cover.
Remove the "jumper" link located in front of the 8 pin I.C.
at the front of the unit.
Replace the existing EPROM with the new (version 5.03 or
later).
Reconnect the mains.
Press [STANDBY]
Press [SELECT]
With the menu cursor highlighting SERVICE press
[SELECT]
With the menu cursor highlighting DEFAULT VALUES press
[SELECT]
Disconnect the mains.
Reconnect the mains. Set the VCO adjustement as follows:
Press [STANDBY]
With the menu cursor highlighting SERVICE press
[SELECT]
With the menu cursor highlighting VCO ADJUSTMENT press
[SELECT]
Use s and t to minimise the scrolling of the picture.
Replace the "jumper" link and press [SELECT].
Will not descramble D2MAC channels:
If the decoder is genuinely faulty (i.e. it used to work
with the same receiver and the receiver tuner is O.K.),
replace I.C. marked DMA2286.
DISCLAIMER
This information is given in good faith, based on several
years of workshop experience involving thousands of repairs.
No responsibility will be accepted for any death, damage or
injury caused either directly or indirectly by the use of
this information. The reader should check the facts himself.
It is assumed and stressed that the reader will be familiar
with good, safe, electronic workshop practice and will be
familiar with all tools, components and terms used. If there
is any doubt about the reader's ability to carry out such
work competently and safely, the work should be referred to
a specialist engineer.
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