Dead FTA receiver power supply

[suiramix]

Hi there,
I tried to troubleshoot a FTA receiver with dead power supply, with good fuse but no outputs voltage. First I did measure the voltage on big capacitor (68uF/400V) and is 103V only...is it normal ??... also had a tiny brown residue on vent... please see attached photos.

[budm]

Re: Dead FTA receiver power supply

There should be about 165~170VDC on that Primary DC filter cap (line voltage x 1.414 = V on the cap). Are the four rectifier diodes close by OK, no leaking liquid from the cap. Put your meter in AC mode and read the AC ripple voltage on that cap for me, be real careful.

[mockingbird]

Re: Dead FTA receiver power supply

suiramix - what are you going to use it for? My FTA has been sitting around collecting dust ever since Beverly got Nagra 2.

[suiramix]

Re: Dead FTA receiver power supply

Hi budm,

Thanks for your help...the AC ripple voltage on primary DC filter cap is 49.5V...my guess is this voltage is way to high than normal !!!
Yes mokingbird, I missed too Beverly, this receiver is for international programs from Europe ...

[suiramix]

Re: Dead FTA receiver power supply

Budm
I replaced the primary DC filter cap (original CapXon had a leakage on positive terminal, see attached photo) but there is no output voltages on secondary circuit ...there is an IC PWM controller NCP 1200AP60 and MOSFET IRF830...please advise ...

[ben7]

Re: Dead FTA receiver power supply

Budm
I replaced the primary DC filter cap (original CapXon had a leakage on positive terminal, see attached photo) but there is no output voltages on secondary circuit ...there is an IC PWM controller NCP 1200AP60 and MOSFET IRF830...please advise ...

Check the rectifier diodes.

[budm]

Re: Dead FTA receiver power supply

So what voltage are you getting on the cap now? 165~170VDC? When that cap was not filtering properly, it will allow large AC to be fed to the circuits and can cause damages to the components.

[suiramix]

Re: Dead FTA receiver power supply

budm,
Yes, the voltage on the new primary DC filter cap is 166.5V DC...the NCP1200P60 has Vcc (pin 6) voltage reading of 6.3V(?) ...the C22 external bulk capacitor is close to MOSFET heatsink and could be dried up (no visible leakage) !

[budm]

Re: Dead FTA receiver power supply

Your bridge is OK, there is a small startup cap by the MOSFET on the heat sink, I would try replacing that cap first, with that much AC ripple before, the IC could be damaged, but try that start up first. That VCC is too low, most SMPS min running voltage spec is about 10V or more.

[suiramix]

Re: Dead FTA receiver power supply

Hi budm,
Again, you're right, I replaced that small start-up capacitor (22uF/16V), the voltage went to 10.8V and the power supply is alive again !!!..Thanks again for you input !!!

[budm]

Re: Dead FTA receiver power supply

Great! Thanks for the feedback.