HOW TO REPAIR THE LNB POWER SUPPLY ON THE SAT RECEIVERS PROFLINE TRSrm
HOW TO REPAIR THE
LNB POWER SUPPLY ON THE SAT RECEIVERS PROFLINE
WE HAVE TO TELL THAT YOU THAT IF YOU HAVE THIS KIND OF FAILURE 99% OF THE TIME
, DEPENDS FROM THE BAD WIRING OF THE EQUIPOTENTIAL GROUND SYSTEM .
THIS MEANS THAT BEFORE CHANGING THE RECEIVER ,
YOU HAVE TO CHECK TO HAVE THE GROUNDING KIT ON THE SAT INPUT CABLE POSSIBLY
BEFORE COMING INTO THE SITE , CONNECTED TO A GOOD COMMON EQUIPOTENTIAL GROUND POINT
AND THE CASE OF THE RECEIVER ALSO CONNECTED WITH HIS GROUNDING SCREW TO THE SAME
POINT OR AT LEAST TO THE COMMON GRUNDING POINT OF THE RACK THAT HAS THEN TO BE
CONNECTED TO THE GOOD COMMON EQUIPOTENTIAL GROUND POINT .
OF COURSE ALSO THE DISH AND THE LNB HAS TO
FOLLOW THE SAME PRINCIPLES .
IF NOT , YOU
WILL CONTINUE TO DESTROY THE RECEIVER WITH LIGHTNINGS AND YOU ARE LIABLE FOR
THIS DAMAGE .
Profline TRSrm receivers are the most common SAT receivers we used all around .There
are two types :
A) The oldest one have only one power supply (typically 16 V) . ON-OFF settings
are possible through the keyboard and display on the front panel .
B) Other series ( see the label on the
back panel of the receiver : “ UNIVERSAL “ ) has also the possibility to drive
universal LNB ( that we only use in very special cases ) . This means having
the possibility to have voltage of 13 or 18 V and a modulation signal of 22 kHz
.The settings are possible through the keyboard and display on the front panel
drive a current no greater that 250 mA . After this current the power supply of
the LNB goes in protection and this is seen on the blinking on the display .
CIRCUIT OF MODEL A
the circuit board there is the possibility to mount also all the components for
the model B ( UNIVERSAL ) , basically not
all the components are put on place on the board . Mainly only the components of the following circuit are
mounted on the board and power the LNB .
You can note for instance that L4 – T2 - Q2 –U15 and R52 are clearly not present . The component that works to power the LNB are in this case the one of the drawing that we have highlighted in the red area
goes toward the F connector with the following input and splitting circuit .
The first circuit
that powers the LNB works in this way :
If from the logic part (uP) the PIN LNBP3 is HIGH
,the transistor Q7 is in conduction (ON) and drive also in conduction Q3 (ON) between
Emitter and Collector . The 15-16V from the main Power Supply goes through R50 (2.2 Ohm ) and power the LNB
. If the voltage on R50 goes high due to a current higher than 250 mA , Q4 limits the conduction of Q7
and so the current .
failures could be :
1) Q3 and/or R50 broken , or some other
component of this simple circuit .
2) Damage on the thin striplines
connecting the circuit to the F connector due to lightning that could also
affect components on the first L Band RF Amplifier/Splitter . Some examples in
the following pictures .
3) Problem on the main Power Supply at
like a fuse from the lightning on the bottom of the printed board
from the RF F connector to the LNB power supply evaporated from lightning !
receiver the current on the case due to lightning was so high that you can
notice sparks in the screws with different materials !
LNB POWER SUPPLY OF
TYPE B (UNIVERSAL )
circuit it is as follow : a switching regulator with 13 and 18 V settings and a
load modulator at 22 kHz (Q5) , driven by the logic commands : LNBP1 ,
you can see that this time on the board R50 and Q3 are not present because don’t
needed in this case( red square) , but the other area is fully populated with
components ( green square ).
skills and component to repair .
Due to the
fact that I am sure that you don’t need Universal LNB Power supply , you can
simply isolate the switching power supply , add in the red square : Q7 and R50 (2.2
Ohm -1W ).
settings on the LNB front panel section you are not able to get the LNBP3
signal HIGH , just short circuit Emitter and Collector of Q7 and Q3 will go in
conduction ON .
You will simply
have permanently 15-16V at the output of the F connector , with the normal current limitation of 250
mA, that is all you need .
option you could short Emitter and Collector of Q3 .You will simply have
permanently 15-16V at the output of the F connector , with the current limitation decided from
the main power supply .
told you that , after some years , in
any case the most easy failure is due to main power supply .
Easy to check the output voltages , we have also given you the drawings of the power supply and a video how to check and repair here : https://youtu.be/DoCkU6qvYx0
On the other hand you can easily find on Internet equivalent power supply with same voltage , currents and dimensions to simply change them .
easy cause of erratic work in locking
and tuning is typically due to erratic oscillation of the 16 MHz Xtal of the
tuner . You can easily change it with an SMD version or a normal metallic version
not least . The first receiver had a fan in a tunnel .If the fan stop ( after
some years ) the receiver goes too hot . Please always check if there is the
fan and works .
If there is
not a fan there is surely a big square of thermal compound that thermally
connect the heater of the main power supply to the top of the cover of the
receiver to avoid the use of the fan (please see the following picture ).
With or without fan you have always to leave a space between the top and the bottom of the rack of the receiver to leave circulation of air !