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help fixing satellite receiver power supply circuit

pharaon

Oct 28, 2014
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ok here's the update
changed the power IC and still the same issue no output voltage
change the Optocoupler and still the same issue no output voltage

so what else could be the issue for no output voltage
 

pharaon

Oct 28, 2014
438
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Once the IC gets its initial "kick starting" it then uses its other separate primary winding to feed thru the 11?ohm resistor and get rectified by D5 to feed C7 / 8 to develop the normal run voltage supply for the IC with a littlle regulation assist from the ZD1 and 2 zener diodes.
ANY of those could ALSO be your BASIC problem instead of the IC.

the issue is R3, it's open circuit so i'll change it and see
 

pharaon

Oct 28, 2014
438
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it was the R3 resistor value of
470kΩ 5%
changed it and now everything working just fine
 

73's de Edd

Aug 21, 2015
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Sir pharaon . . . . .

Good Show !
That certainly wasn't expected . . . . as . . . IT . . . and 3 other like resistor types on the board, have physical sizing appearing to be of 2 watt ratings and METAL film construction, vice being the CARBON film used on the other small units on the board.
Its function initially is being the current limiter / voltage dropper that feeds into the shunt regulator zener diode and storage capacitor that feeds the Vcc voltage into that "power supply chip".
Once the supply kick starts on to give a start up train of pulses to the internal power FET of the chip, then a separate power winding and a rectifier diode feeds the RUN Vcc to the unit as the constant run Vcc supply.
That chip is running 24 9/64ths hrs a day in low power mode, if not being run at the the fully powered up sat receiver function.
The instant that you plug that unit into ac power, that is what initially starts the supply into its low power standby mode, until demand is made of the main board , either by power switch or remote control, which then commands the unit to shift to full power mode.
Now in a WORST case situation, if that 470 k resistor had fed into a shorted zener regulator diode, ohms law tells us that 350 VDC thru a 470K resistor will ONLY let .00074 ma of current be dissipated in the resistor . . . . .that correlates to a paltry 0.26064 watts dissipation within the resistor.
So o o o o o o one must expect your failure mode to be a loss of connectivity of the clinched on two ball cap ends of the resistor to the resistance element ends.
Or posssibly a floating ring joint solder connection at its leads to the pcb, if that resistors leads initially had an oxidized layer * on them back at flow solder bath manufacturing time and did not fully wet and reflow in that short heating duration.
* Too long of a time in storage, or being in environmentally poor storage conditions.

Since you had a SOFT failure and DID NOT experience a HARD FAILURE, that would leave a blown fuse, FWB rectifier diodes, the .5 power resistor in the I.C. ground return , or have a shorted power FET within the I.C., you may STILL have a good I.C. for future use if ever required.

I was just about to submit this mark-up below . . . . but will do it also . . . for the info that is to be gleaned from it in similar cases.

TECHNO INFO . . . . .

VIPER.png




73's de Edd . . . . .

Whenever someone calls me ugly, I get super sad and hug them, because I know how tough life is for the visually impaired.


.
 

debe

Oct 15, 2011
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Oct 15, 2011
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It was pointed out in thread 10 to check that resistor but you said it was ok. That is a common fault with that type of SMPS.
 

pharaon

Oct 28, 2014
438
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I was just about to submit this mark-up below . . . . but will do it also . . . for the info that is to be gleaned from it in similar cases.
very helpful 73's de Edd thanks alot

It was pointed out in thread 10 to check that resistor but you said it was ok. That is a common fault with that type of SMPS.
that's true, i don't know how could i miss reading the value , could saved lot of time on me
 

Boybiafra

May 15, 2022
1
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May 15, 2022
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Please I want to know the the values of ZD1 and ZD2 to enable me replace the zener Diodes immediately. I equally want to know the values of mains smoothing capacitor, first snubber capacitor for the secondary side. Thank you
 

73's de Edd

Aug 21, 2015
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If you pull those two clear glass zener diodes, I almost always find that the voltage is stamped on them in black as 2- 3 digits plus an A or B tolerance.
Same on the blue ceramic buffer, as usually picofarads (sometimes low nano) and at a 3-5 Kv rating.
Definitely the E cap is marked on this one we see 4 which could be the first 47 ufd or just the first 4 of the caps voltage rating.
 
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