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Astron SS-25 (NON-M Model) PS Low Output Voltage

Discussion in 'General Technical Questions and Answers' started by KB3GWQ, Oct 12, 2017.

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  1. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    I got a used Astron SS-25 PS for free from someone a week ago and have been using it OK with my ICOM IC-476PRO for the past few days. Today I went to turn the radio on and the radio wouldn't come on. Checked all the cables, etc. first and then checked the output on the PS at the terminals and it's ouputting 2.2V. I grabbed a backup PSU I use and the radio works fine again.

    Not sure how to diagnose this. I opened up the unit and didn't see anything obvious. Appreciate any advice. I found this: http://www.n5na.net/s9y/index.php?/archives/28-Repairing-an-Astron-SS-25-and-SS-30.html. So a possibility would be removing the diodes and checking them?
     
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Sure, why not?

    But switchmode power supplies are complex, and failures have many causes.
     
  3. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    Well I figure the failure may just be because it's old and unknown how long it's been sitting for. The PS wasn't underrated for the radio and it never ran that hot when I was using it.
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Could be "old age," or at one time it experienced a lightning transient, or almost anything.

    The SS-25 in my experience is actually quite reliable, but they sure don't do well with nearby lightning strikes.:p
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Does the voltage adj pot change the output voltage at all ? A dirty pot makes strange things happen.

    Good Luck.
     
  6. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    I thought the voltage pot is only going to adjust it like a volt or so, or am I mistaken? I suppose I could try it just for kicks.

    I did remove the few diodes that were mentioned in that link in the first post (D17, D18, and another one nearby) and they are testing out OK.
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    You are correct. That is if it is working properly.

    If the pot is on a dead spot (Dirty) the output can be way off.

    Just Bump it. It is a long shot that is the problem, But is easy to try.

    Good Luck.
     
  8. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    I'll give it a try tonight. If that doesn't work the gentleman who gave it to me has serviced these before and said if he remembers correctly there was a large 1 ohm resistor somewhere in there and those were the most common thing he replaced in them.

    Will check that out as well if the pot doesn't do the trick.
     
  9. G4COE

    G4COE Ham Member QRZ Page

    I'd be checking electrolytic capacitors, for bulging, domed tops or leakage.... this alone may not indicate if they have gone high ESR.

    Should any of these need changing DO NOT use 'bog standard' capacitors use 105 deg. C. temperature rated types that have low ESR.

    Dave
     
    K8AI likes this.
  10. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    I did a visual inspection they all looked OK. But I do have a heathkit cap checker. And yes, I always use 105C whenever I redo caps in anything. But will make sure to use low ESR series as well for this if it requires it.
    I typically use Panasonic 105C's when I can for any project.
     
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