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 TRSrm

AT FIRST 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 .

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The 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 .

Both can 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 .

POWER SUPPLY CIRCUIT OF MODEL A

While on 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

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The voltage 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 .

Typical 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 15-16V .

 

 

Strip blown like a fuse from the lightning on the bottom of the printed board

 

 

 

 

 

Stripline from the RF F connector to the LNB power supply evaporated from lightning !

In this 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 )

The general 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 , LNBP2 

In reality 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 ).

 

Need some 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 ).

If changing 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 .

As extreme 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 .

 

FINAL REMARKS

 

We have 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 .

Another 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 .

Last but 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 !

 

APPENDIX : BLOCK DRAWINGS AND PICTURES OF AN UNIVERSAL LNB (Ku Band )

13V : Vertical Polarization

18V : Horizontal Polarization

No 22 kHz Tone : OL = 9.75 GHz

22 kHz Tone : OL = 10.6 GHz