VHS DVD combo that still won't power up

Discussion in 'General Electronics Chat' started by Rolland B. Heiss, Apr 16, 2015.

  1. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    I'm a bit bummed out that I haven't been able to get power back in relation to my once working VHS/DVD combo player. I took it apart and one capacitor was clearly bulging and I thought, 'AH! Therein lies the problem!!!'. However I replaced the one and only obvious problem and still no power. :( So I figure that despite a visual inspection there must be other capacitors in that section of the circuit that are bad without any visual indications. So, must I unsolder each capacitor in order to test them or is there a better way that is not so time consuming? I'm fairly new to all of this as many of you know or have already gathered and therefore any advice is always appreciated.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,249
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    Check things up stream from the cap; maybe it took something out. Maybe there were some fuses. Maybe a resistor opened.
     
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  3. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    Fuse is good. Haven't checked a resistor yet however. Thanks for the input!
     
  4. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Temporally disconnect and 'dummy' the PS output then see if the PS 'boots up'... Note: A 40W 120v incandescent lamp should adequately serve as a dummy resistor for most SMPSs...

    Best regards
    HP
     
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  5. debe

    Well-Known Member

    Sep 21, 2010
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    Would be beter if people posted pictures of their gear, like your powersupply. Some SMPS have a resistor to kick start them, if it goes high they wont start.
     
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  6. sheldons

    Active Member

    Oct 26, 2011
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    Make and model and ill look at the sm if ive got it.....
     
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  7. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    Thanks for the suggestion! Interestingly enough I was reading an instructable this morning in which someone used several christmas lights as 'dummy' resistors which also sort of doubled as 'dummy' fuses in order to charge certain things with a 12 volt lead acid battery. I'd never thought about using lamps or christmas lights in such a way until I read that and here you are giving me similar ideas but in this instance not for charging but rather isolating a problem. I swear I'm going to figure this problem out eventually!!!!
     
  8. Rolland B. Heiss

    Thread Starter Member

    Feb 4, 2015
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    I'll try to keep that in mind. I was done for the day when I posted this and frankly didn't want to see the garage or the workbench again until another sunrise came around! There comes a point on certain days every now and again when you are either too tired or just too frustrated to press forward any further.
     
  9. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    FWIW, in the applications described in your post, the conventional term is 'ballast resistor{s}':) --- Note also that when using lamps 'off label' it is important to determine their technology (e.g. Incandescent, LED, Discharge, EL, etc...) only incandescents are true (albeit 'swinging') resistors (i.e. R=[E^2]/Rated_Power only under specified operating conditions and, hence, filament temp) --- Other devices exhibit disparate electrical characteristics...

    Best regards and good luck! :)
    HP
     
    Last edited: Apr 18, 2015
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  10. sheldons

    Active Member

    Oct 26, 2011
    616
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    Ok if you remove the feed to the line op stage, attach a 40w lamp as a dummy load on the supply you can check on switch on if you have ht and if you supply the make and model I can supply the sm so you will know what ht voltage should be present. ..
    If ht comes up and is stable you know at least the primary side is working and the secondary side is ok ....if the set is stuck in standby you may have a fault nvm wise or a fault on one of your other supply rails.....I once had a dead set due to a faulty audio ic....make and model required
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    make and model of TV, any pictures of the pcb,with the chip numbers of the psu.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    There's usually only one or two electrolytics that "take stuff out" - usually there's an error sampling capacitor and/or an aux supply cap that supplies the control chip/discretes, sometimes they're one and the same. Sometimes the offending capacitor is only 1uF, but may be as big as 47uF - the smaller ones I always replace outright with a film type, the larger ones can't easily be replaced with a bulky non-electrolytic, so I replace the electrolytic with a high temperature low ESR type and pad it with a non-electrolytic on the print side. You probably want to aim for at least 0.22uF if it will fit the available space. Failure of this capacitor usually causes a resounding PHUT, so I attend to it whether it needs it or not.

    Excessive SMPSU frequency ripple on any of the secondary side filter electrolytics can upset things - possibly preventing the front panel micro from initialising.

    Most of the component supply houses that specialise in consumer electronics, stock kits of electrolytics for popular models to do a "shotgun" replacement service. Its nice when a faulty electrolytic owns up by bulging it's top, but they don't all do that, and if one is worn out - the rest aren't far behind.
     
  13. debe

    Well-Known Member

    Sep 21, 2010
    947
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    Wondering where TVs came in to the discution? I thaught he was refering to a VHS/DVD combo player, which is a diferent beast.
     
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