powering up old unused electrinics equipment

Discussion in 'General Electronics Chat' started by paulmars, Jul 31, 2014.

  1. paulmars

    Thread Starter Member

    May 13, 2010
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    I remember in electronics school in the 1980s we learned that the best way to damage a very old piece of electronic equipment was to power it on with full voltage. After a long time with no power caps go to zero ufd, which will pass the full voltage and burn out other components. Something like that. Im looking on the internet for info about this, but I cant find any. Do you know of any?

    tks,
    pa
     
  2. AlphaDesign888

    New Member

    Jul 27, 2014
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    Dispose of them at the tip. Those big machines that crush everything up are fun to watch. So much POWER! Hydraulic power!
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    AFAIK your memory is coirrect, the caps tend to blow. The way to recover is to soft start them by slowly increacing the line voltage over a period of hours to days.

    A Variac is most helpful in this task.
     
  4. bance

    Member

    Aug 11, 2012
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    Another way is to use an old fashioned light bulb in series.......

    HTH Steve.
     
  5. paulmars

    Thread Starter Member

    May 13, 2010
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    huh?

    The message you have entered is too short. Please lengthen your message to at least 10 characters.
     
  6. Lestraveled

    Well-Known Member

    May 19, 2014
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    I don't think that this would be a good idea in this case. Bringing up old equipment you want to start at low input line voltage. The lamp filament has the lowest resistance when it is cold so the line voltage would be highest at turn on. This is not desirable.

    A variac is the right device.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I agree with the variac - IF you can disconnect the rest of the device from the power supply. Some unknown equipment might have unknown isues with low voltage, unregulated power rails.

    ak
     
  8. Gdrumm

    Distinguished Member

    Aug 29, 2008
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    Just today, I picked up an old pc.

    It was one of the dirtiest I've ever seen inside (and out).

    I blew it all out, plugged it in, and it tried to go.

    Within about two minutes, it shut down. Kaput.

    I salvaged the 500mb stick of ram.

    I checked the HD and it was dead, wouldn't spin up.

    My guess is that as it was warming up, something blew in the MB or Power Supply.

    In the case of a PC, would a Variac have worked?
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The PC will most likely have a SMPS.
    This will not work well when the input voltage is to low.

    The variac approach will work for equipment that uses a linear power supply.

    Bertus
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I've just dumped a dozen old XP boxes I no longer have room or use for!

    No, unless you started with only 10 - 20 volts low.

    But failure was a likely due to dirt causing shorts or overheating, as anything else.

    A variac is fine for simple equipment, particularly those which have higher voltage rails and capacitors, eg valve based equipment. The older HV electrolytic capacitors are more prone to aging through lack of use, than modern LV ones.

    But complex equipment, particularly if it has a switched mode supply is best tested in stages, starting with the power supply.

    @paulmars

    What do you actually want to test run?
     
  11. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the veriac will not workon some old equipment, tube type equipment requires a minimum voltage before the rectifyer filament heats enough to conduct. it is best to either test the filter caps or replace them before turning on. paper caps also go bad with age. carbon resistors also age up in resistance.
    there are several radio sites for people who like the old "boatanchors" and restore them. look up "glowbugs" and "boatanchors" .
    also look up the brand of he old stuff, there might be forums and websites for collectors.
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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    6.3 volts was a common heater supply, if I remember correctly.

    Usually this was supplied from a separate transformer or winding so a second test on valve equipment might be to disconnect the HT supply (usually in the region 170 to 350 volts) and see if the heaters light up.

    The first test would, of course, be a continuity test on the heater chain.
     
  13. bertus

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  14. alfacliff

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    Dec 13, 2013
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    studiot, pull the rectifier, or open the leads from the rectifier to the transformer, a shorted filter cap can burn the transformer very quick. the reason the variac wont work is because the filament of the rectifier would bet how much voltage from a 110 volt primary transformer that usually steps down to 5 volts if the primary was only getting 30 or so volts. would the rectifier be putting out enough to form the caps? similar for a series filament string.
     
  15. alfacliff

    Well-Known Member

    Dec 13, 2013
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    pull the outputs from the smps and put on a load for the 5 volt output to test the power supply for pc's. an amp or so load on the 5 volt line should load it enough for the supply to come on. then you have to know how to get the supply to turn on.
     
  16. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Yes I meant to say that many pieces of equipment are made from plug together modules, so can easily be disconnected for testing.

    Why would a heater supply have a filter cap?

    There are indeed many types of valves (Mullard only ever called then valves except for CRTs), just as there were many manufacturers who did not use an E classification for 6.3 volt heaters. Even Mullard made a few 6.3v valves with other designations.

    However a quick scan of Ball "Radio Valve Data" reveals that 6.3 volts is consistently the most popular voltage.

    But really so what?
     
    Last edited: Aug 1, 2014
  17. bertus

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  18. alfacliff

    Well-Known Member

    Dec 13, 2013
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    tube (valve) filament supplies are usually ac unless for some battery powered stuff from LONG ago.
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    Anything with a SMPSU will do nothing up to a certain voltage then spring to life with full voltage on the secondary side electrolytics.

    If they're big enough to make a serious mess if they explode, they should be disconnected and re-formed individually. Once that's done the secondary side caps can be put back and the mains in reservoir caps can be edged up gently with a variac.

    Presumably modern PSUs with a PFC front end will make life a little more interesting, since the PFC front end is usuall in the form of a boost converter in front of the reservoir cap. Probably another one that should be unhooked and done individually.
     
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