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Thread: Another VAST box dead power supply??

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    Update: I bought an FR302 diode from Jaycar and a new cap - C10 and after replacing them it works fine. Let's hope for another 7 years!

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    Quote Originally Posted by gungadin View Post
    Update: I bought an FR302 diode from Jaycar and a new cap - C10 and after replacing them it works fine. Let's hope for another 7 years!
    Thanks for the update.

    Pleased you got it sorted.

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    The old UEC 141 240v box died again today. I replaced the 1M resistors on the power supply board some years ago and this time the culprit was C10.

    A quick rattle through the salvaged caps box turned up a replacement (diode was fine) and within 15 minutes I'm back on air.

    I trust UEC sorted out their dodgy component supplier for the later models - - -
    4.6m C band dish, numerous Strong boxes, GTsat V8 Nova and even an old BMAC somewhere ---

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    Hi, Word of advice , change ALL the PSU caps! they all have a tendency to fail. Just order some 2200uf @ 35V caps (x6) there is plenty of room on the PCB & they will never fail again. Hope this helps.

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    Quote Originally Posted by Softek2 View Post
    Hi, Word of advice , change ALL the PSU caps! they all have a tendency to fail. Just order some 2200uf @ 35V caps (x6) there is plenty of room on the PCB & they will never fail again. Hope this helps.
    Yeah Softek I realise that. I'll get around to it eventually, one day, in my spare time. (I wish!)
    4.6m C band dish, numerous Strong boxes, GTsat V8 Nova and even an old BMAC somewhere ---

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    Default DSD4121 power supply

    Hi all. Just repaired one of these. The first item to fail will be the 2.2 meg startup resistor. These cracked carbon resistors will fail when there is a high voltage gradient across them. Some power supplies might have 2 resistors, each 1 meg in series. This one had 1 only 2.2 meg, and it was open circuit. NOTE: Always replace resistors with high voltage across them with METAL FILM resistors to avoid failure.
    The other component that had failed was D5. It is a small diode beside the transformer. This one was burnt to dull grey, and measured 58 ohms in both directions. As the frequency of the oscillator is fairly high, I used a FR105 fast recovery diode. I doubt that the likes of a 1N4007 would be satisfactory in this application.
    All electrolytic capacitors tested OK. The power supply now works fine.
    Hope this helps.
    Cheers
    Geoff

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    Default replaced power supply for UEC Altech 4121 but still dead

    Hey Guys. Wondering if any of you might have some ideas on this. I was given what the owner thought was a working UEC Altech 4121 to receive VAST. But I wouldn't power up. I ordered a replacement power supply from for $30 but the unit still won't power up. I notice that a capacitor on the PCB for the serial connection in the middle has popped but I was hoping that would not be a problem unless I was using the serial port.

    Here are a few pics... if anyone has any bright Ideas that would be awesome.



    (I have also misplaced the remote somewhere but surely this will show some kind of sign of life without the need for a remote... right?)

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    Is that an electrolyte stain or a burn?

    I'd be looking at all the usual suspects... mostly other caps.

    If it's a burn, that may suggest a high voltage spike and the main board may be stuffed.

    You don't need a remote to power on/off and channel change.

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    That is contact cement that is ageing. Just unplug the PCB as it will not affect the operation of the decoder.

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    OK thanks guys, I'll just unplug that little PCB and give it another go.

    I've already had a look at both the original power supply board and the replacement carefully and I can't see and busted looking components or cracked solder. I'll have a look at the main board too.

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    Quote Originally Posted by divdivdiv View Post
    I've already had a look at both the original power supply board and the replacement carefully and I can't see and busted looking components or cracked solder. I'll have a look at the main board too.
    Often some components fail without any visible issues.

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    Yeah. Unfortunately looking at them is about the limit of my technical abilities. Could any of you guys recommend someone who might be able to repair my UEC box? I'm based in Sydney. Happy to pay cash to a hobbyist who thinks they're up to it. At the moment all I've got is a dead box and two (likely) perfectly good power supplies.

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