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Question about DC power supply

Discussion in 'Ham Equipment' started by Okiksapa, Feb 11, 2012.

  1. Okiksapa

    Okiksapa Member

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    Hello - I've been a member for several months, but have never posted.



    I picked up an Astron VS-35M power supply. When I plug it in and turn it on does there need to be a load on it in order to adjust the amps and the voltage? When I turn the knobs, the meters don't move at all. I can hear it humming but nothing else. I've never had a power supply before and the one I picked up didn't have a manual with it, and I know virtually nothing about these things.

    Thanks.
     
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  2. Okiksapa

    Okiksapa Member

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    One question answered

    I did find out that with no load the current needle will not read anything, so just need to know if I should be able to adjust the voltage with no load. I'm in the mode of seeing if I get a bum deal on this PSU right now, so any help for a newbie would be great. Thanks.
     
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  3. Robb

    Robb Yup

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    Never used a power supply before?
    OK.

    Did you hook up a radio and check it out on the supply yet?
    Set the voltage at 14.1v with the radio turned on.
    Observe proper polarity - very important.
    Don't transmit until you have an antenna or a dummy load on it.
     
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  4. mackmobile43

    mackmobile43 Jock Supporter

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    Think about it, does a battery charger show any charge until it's presented with a load>? no

    Give it a load and adjust, start with the variable control at it's lowest point to start with and slowly increase until the desired voltage is reached.

    Do not transmit any radio without an antenna or rf terminator connected.
     
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  5. Beetle

    Beetle Well-Known Member

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    Yes, you need a load for the AMMETER to give an indication, but the VOLTMETER should read up-scale as soon as you turn the PS on. If it doesn't, use a VOM/DVM and check the voltage at the terminals. If you get some value of voltage on that meter, see if it's adjustable.

    If it is, the voltmeter circuitry is defective - the meter itself or something in the wiring. If you get no voltage reading, the PS might need some repair.
     
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  6. Okiksapa

    Okiksapa Member

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    Thanks for the replies - (by the way I'm a retired Army CW4 - I see you were Navy) - Just so I don't do anything wrong, how do I hook up the DVM to the terminals. I know that red is hot, but do I just ground to the chassis of the PS?

    If the voltmeter circuitry is bad - where would I begin to look for something amiss?
     
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  7. Okiksapa

    Okiksapa Member

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    Nope, never used a PS before. I don't have a radio that I can hook it up to. All I have for a radio right now is a VX8R HH. I'm just trying to see if it works properly in the mean time. Is there something else I can hook up to it to load it down to see if it works?

    I came upon this PS and it was a 'decent' price so didn't want to pass it up. I knew getting something used was a risk, but I'm here to learn and if needed to fix stuff, so just trying to get going down the 'rectified' path (sorry, couldn't resist the pun). Thanks.
     
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  8. Okiksapa

    Okiksapa Member

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    That totally makes sense now that I think about it. I'm concerned about the voltage, though. I just want to make sure all is working before I hook anything up to it, but guess I need to hook something up to put a load on it. How about the voltage, anything I can hook up to that I might have laying around to check out the unit? Thanks.
     
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  9. mackmobile43

    mackmobile43 Jock Supporter

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    Do you have a volt/ohm meter? if it supposed to show voltage as Beetle says then this meter would indicate voltage output even if the unit's meter does not as far as testing with something laying around you can use anything that requires dc voltage in the range of the power supply, just make sure of the the polarity is correct before tuning on the power supply.
     
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  10. Okiksapa

    Okiksapa Member

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    Here's what I have so far on this:

    1. Fuse is okay
    2. DC adjustment knob was loose, tightened that.
    3. Hooked up DVM to it and got that following:
    - 1.86-1.89 VDC no matter where the voltage adjustment knob was

    So - does it look like my voltage adjustment circuitry is bad? It seems so to me. If so, where do I begin to troubleshoot this? What do I test with the DVM? What parts might I need? I'm assuming it will need some soldering to get this fixed.

    I appreciate your advice and assistance with this.
     
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  11. Okiksapa

    Okiksapa Member

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    I hooked up DVM again and took off the cover to look around.

    Nothing seems loose or broken inside.

    I did notice that when I rotate the voltage adjustment knob that the DV volts drop from 1.89 to 1.86 when I rotate clockwise. That seems strange, as the volts should increase.
     
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  12. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Sounds to me like the voltage regulator chip is shot. When the voltage regulator takes a dump the typical output voltage is around 2 volts which is what you are seeing. I am pretty sure you need a new LM723 regulator chip. Either that or one of the pass transistors on the heat sink is shorted and allowing too high a voltage to appear on the output and the safety protection is constantly being tripped which limits the output to jst a volt or two. An LM723 regulator chip is just a couple dollars and plugs into a socket and would be easy to replace. The transistor however is a bit harder but not difficult IF you are familiar with electronics.
     
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  13. mackmobile43

    mackmobile43 Jock Supporter

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    I did not know there was a dual in line package version of this chip, I have used the metal can package which I have a extra or 2 of if needed.

    http://www.ti.com/lit/ds/symlink/lm723.pdf
     
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  14. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    Man where have you been? :laugh: I have a Tripp Lite power supply that must be at close to 20 years old and it has the DIP package style in it. You need to get out more often Mack. :D
     
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  15. mackmobile43

    mackmobile43 Jock Supporter

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    The only use I've had for the lm-723 was in a bias circuit and never had to open any of my power supplies for servicing so that's why I was surprised, to too have a Tripp Lite now you make me want to tear into it and touch the guts.
     
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