cs4000pro, no 13V and 18V

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coolsat4

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May 31, 2006
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Hi, need help.
I have coolsat4000pro. I mesure 23VDC on connector to LNB - back of receiver. I don't mesure 13VDC and 18VDC needed for LNB operation. The 23V is even present with LNB power off in dish settings.
Please, need help how to fix.
Thank You
 
PSB

PSB

On vacation
Nov 5, 2003
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WOW! WAY too much! Did you recently flash it with new software?
 
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coolsat4

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May 31, 2006
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PSB said:
WOW! WAY too much! Did you recently flash it with new software?
No. I am using factory installed software. I am afraid to connect it in this condition. Is it software or hardware problem?
Thanks
 
PSB

PSB

On vacation
Nov 5, 2003
1
5
If you have not changed the software than its got to be hardware!

Try a Vertical transponder then a Horizontal Transponder for voltage!
 
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coolsat4

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May 31, 2006
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PSB said:
If you have not changed the software than its got to be hardware!

Try a Vertical transponder then a Horizontal Transponder for voltage!
Tried. Does not change voltage.
Thanks
 
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dish_in_the_sky

SatelliteGuys Family
May 18, 2006
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Try checking the output regulator on the SAT input line.

There will be an inductor carrying the LNB power to the sat input on the receiver. Trace that to the emitter on a powr transistor, possibly through a fuse or polyswitch (resettable thermal fuse) and/or a low value resistor.

Most likely problem is a bad series pass transistor.

They'll use a series pass transistor with a heatsink (maybe the case is used as a heatsink) to derive the 13/18V. Switching reference voltages to drive that transistor supplies the LNB power, and setting that voltage to 0 will turn the transistor (and LNB power) off. 2 pins on the microprocessor will most likely be used to switch the voltages.



For a bipolar NPN transistor, the reference voltages on the base should be
13.7V--13V out (emitter)
18.7V--18V out (emitter)
0V to 0.4V--0V out (emitter)

The output voltage will be on the emitter, and the collector will have the highest (relatively constant) voltage opn it, probably ~23V based on your measurement.

The transistor could dissipate ~5W if loaded at 0.5A at 13V out, so it WILL require a heatsink. Use at least a 1A, 40V, 20W rated part (ideally same or better ratings than the existing part.)

Of course they might use a regulator IC, switchiing regulator, etc. In those cases find out what the parts are, what they're doing and troubleshoot it.

They have to use the microprocessor to control the voltage and to turn it off, and they have to use an inductor to get it to the satellite input. They have to use a capacitor to get the sat signal separated from that DC power. Those are the starting points from which to reverse engineer and troubleshoot the circuit.
 
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coolsat4

Thread Starter
Active SatelliteGuys Member
May 31, 2006
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dish_in_the_sky said:
There will be an inductor carrying the LNB power to the sat input on the receiver. Trace that to the emitter on a powr transistor, possibly through a fuse or polyswitch (resettable thermal fuse) and/or a low value resistor.

Most likely problem is a bad series pass transistor.

They'll use a series pass transistor with a heatsink (maybe the case is used as a heatsink) to derive the 13/18V. Switching reference voltages to drive that transistor supplies the LNB power, and setting that voltage to 0 will turn the transistor (and LNB power) off. 2 pins on the microprocessor will most likely be used to switch the voltages.



For a bipolar NPN transistor, the reference voltages on the base should be
13.7V--13V out (emitter)
18.7V--18V out (emitter)
0V to 0.4V--0V out (emitter)

The output voltage will be on the emitter, and the collector will have the highest (relatively constant) voltage opn it, probably ~23V based on your measurement.

The transistor could dissipate ~5W if loaded at 0.5A at 13V out, so it WILL require a heatsink. Use at least a 1A, 40V, 20W rated part (ideally same or better ratings than the existing part.)

Of course they might use a regulator IC, switchiing regulator, etc. In those cases find out what the parts are, what they're doing and troubleshoot it.

They have to use the microprocessor to control the voltage and to turn it off, and they have to use an inductor to get it to the satellite input. They have to use a capacitor to get the sat signal separated from that DC power. Those are the starting points from which to reverse engineer and troubleshoot the circuit.
Thank You very much. It sounds very profesional.
I will try this and I will let you now.
Thank you
 
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dish_in_the_sky

SatelliteGuys Family
May 18, 2006
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Careful :)

DON'T SLIP with the meter probes!

Take this frome someone who has--and had to pick up the pieces and fix even more afterward:)
 
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coolsat4

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May 31, 2006
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dish_in_the_sky said:
DON'T SLIP with the meter probes!

Take this frome someone who has--and had to pick up the pieces and fix even more afterward:)
Very funy!
Hi, thanks to you I needed 1h and found that it is LM317 - 3-terminal adj. voltage regulator- wich controls the voltage to LNB. Possibly controled by transistor pnp on adj pin
on input = 23.82V
output = 23.76V
adjust = 21.6V
I found that resistance betw. input and output is few oms - possible short
If I change chanels , I can see less than a volt diference betw H, and V TP's on adjust pin.
Any sugestions. How to procede next?
Thank You.
 
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dish_in_the_sky

SatelliteGuys Family
May 18, 2006
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LM317 behaviou

The LM317 needs ~2-3V drop between IN and OUT to regulate properly. The OUT pin stays 1.25V higher than the ADJ pin when in regulation.

You can try connecting the ADJ pin to ground through a 10 ohm resistor, see if the output drops to 1.25V. The voltage across that 10 ohm resistor should not be more than 0.1VDC (~ 10mA current = ADJ pin current + voltage divider current.) If these things are true, the LM317 is at least basically functional, thogh it might be a little leaky.

If the part reads a few ohms between IN and OUT (+ to IN) with power removed and the capacitors discharged (to ensure a correct resistance reading,) then find out why. Resistance readings in-circuit can be misleading at times, but a few ohms is pretty definitely bad in this case (barring an external component across the LM317 that's shorted)

Normally the ADJ pin current does not exceed 50 microamps, if significantly more than this with 2-3V across in-out, then the regulattor is bad.

They are probably switching resistor values to ground (with NPN transistors) in order to adjust the output voltage, this is very easy to do with an LM317. Driving the ADJ pin to ground will yield an output of 1.25V (essentially off for an LNB.) 2 transistors would be enough to do so using 2 series resistors for R2, one transistor shorts out the bottom resistor, the other shorts out both resistors. Both off=18V, 1 on (bottom R shorted)=13V, other on (both R's shorted)=1.25V (off.) Vout=1.25 * (1 + R2/R1 ) R2 goes from ADJ-ground, R1 from OUT-ADJ. R1 is ~120-240 ohms to ensure leakage current and ADJ pin current do not affect output regulation.

A diode is often connected across the LM317 in-out pins, K to in pin, A to out pin, to shunt reverse current around the regulator if the input suddenly drops or a spike comes down the cable.
 
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coolsat4

Thread Starter
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May 31, 2006
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dish_in_the_sky said:
The LM317 needs ~2-3V drop between IN and OUT to regulate properly. The OUT pin stays 1.25V higher than the ADJ pin when in regulation.

You can try connecting the ADJ pin to ground through a 10 ohm resistor, see if the output drops to 1.25V. The voltage across that 10 ohm resistor should not be more than 0.1VDC (~ 10mA current = ADJ pin current + voltage divider current.) If these things are true, the LM317 is at least basically functional, thogh it might be a little leaky.

If the part reads a few ohms between IN and OUT (+ to IN) with power removed and the capacitors discharged (to ensure a correct resistance reading,) then find out why. Resistance readings in-circuit can be misleading at times, but a few ohms is pretty definitely bad in this case (barring an external component across the LM317 that's shorted)

Normally the ADJ pin current does not exceed 50 microamps, if significantly more than this with 2-3V across in-out, then the regulattor is bad.

They are probably switching resistor values to ground (with NPN transistors) in order to adjust the output voltage, this is very easy to do with an LM317. Driving the ADJ pin to ground will yield an output of 1.25V (essentially off for an LNB.) 2 transistors would be enough to do so using 2 series resistors for R2, one transistor shorts out the bottom resistor, the other shorts out both resistors. Both off=18V, 1 on (bottom R shorted)=13V, other on (both R's shorted)=1.25V (off.) Vout=1.25 * (1 + R2/R1 ) R2 goes from ADJ-ground, R1 from OUT-ADJ. R1 is ~120-240 ohms to ensure leakage current and ADJ pin current do not affect output regulation.

A diode is often connected across the LM317 in-out pins, K to in pin, A to out pin, to shunt reverse current around the regulator if the input suddenly drops or a spike comes down the cable.
Hi, and thank you.
I did not have at the moment 10ohm resistor. I found 1k. If does not help al buy
10 ohm and will check again.
Grounded adj pin with 1k as it is on the board (assuming there is ~2.7k to gnd in
circuit) so will get less than 1k to gnd. Voltage on output changed from 23.74v to 22.97v. I checked resistance betw. in and out pins it is 7ohms. I mesure 74mv voltage drop betw in and out pins. There is a diod connected to output and one of the pins of a mini transistor and resistors.
Let me know if Ihave to test it with 10ohm.
Thank you.
 
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dish_in_the_sky

SatelliteGuys Family
May 18, 2006
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Testing LM317...

Replace the LM317 and continue troubleshooting. The output voltage should have dropped significantly when you added that 1K resistor to ground. A 10 ohm resistor would give a higher confidence in testing the LM317.

Note that replacing the LM317 may not appear to fix it. If it does, great! If not, we'll continue troubleshooting.

The diode at the LM317 output is probably to protect the regulator if someone connects 2 receivers together, with this receiver's LNB power off. It would prevent the 13V/18V sourced by the other receiver from appearing at the regulator. The transistor might be used for overvurrent sensing (the LM317 can source 1-1.7A and the receiver only needs to source 0.5A)
 
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coolsat4

Thread Starter
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May 31, 2006
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dish_in_the_sky said:
Replace the LM317 and continue troubleshooting. The output voltage should have dropped significantly when you added that 1K resistor to ground. A 10 ohm resistor would give a higher confidence in testing the LM317.

Note that replacing the LM317 may not appear to fix it. If it does, great! If not, we'll continue troubleshooting.

The diode at the LM317 output is probably to protect the regulator if someone connects 2 receivers together, with this receiver's LNB power off. It would prevent the 13V/18V sourced by the other receiver from appearing at the regulator. The transistor might be used for overvurrent sensing (the LM317 can source 1-1.7A and the receiver only needs to source 0.5A)

Hi, I just found 10ohm resistor. I will test again and if i dont get 1.25V I vill replace
LM317.
Thank you.
 
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coolsat4

Thread Starter
Active SatelliteGuys Member
May 31, 2006
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coolsat4 said:
Hi, I just found 10ohm resistor. I will test again and if i dont get 1.25V I vill replace
LM317.
Thank you.
Hi again.
I was going to go in bed, then I sed I have to check it now.
So 10ohm drops output voltage to 21.51V only.
I will buy Lm317 and will cross my fingers.
Thanks again for the support.
 
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coolsat4

Thread Starter
Active SatelliteGuys Member
May 31, 2006
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Problem solved

HI, and Thank You.
I replaced LM317 as You sugested and bang everething is ok. Now I have 13V, 18V, and 0V when off. When I removed IC I noted that there was no heat transfer compound between heat sink and IC. I did it the proper way and now is ok
Thank You guys You are grait.
 
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dish_in_the_sky

SatelliteGuys Family
May 18, 2006
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Careful, the tab is live!

The tab on the LM317 is at Vout as I recall. Make sure that is not a problem. (i.e. is the heatsink isolated or grounded?

You were right to use heatsink compound.

I'm glad that fixed it!

EnjoY!
 
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coolsat4

Thread Starter
Active SatelliteGuys Member
May 31, 2006
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dish_in_the_sky said:
The tab on the LM317 is at Vout as I recall. Make sure that is not a problem. (i.e. is the heatsink isolated or grounded?

You were right to use heatsink compound.

I'm glad that fixed it!

EnjoY!
I am glad too that is fixed.
The heatsink is under power and is isolated from gnd ( the tab of LM317 is under power - the ouput, You are correct)
Thanks for the help again.
 
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