Suitable replacement for PTC thermistor?

Discussion in 'General Electronics Chat' started by Chris Ronayne, Apr 24, 2013.

  1. Chris Ronayne

    Thread Starter New Member

    Mar 11, 2013
    10
    0
    Hi all,

    I am repairing a 1996 20" SAMSUNG TV-516 colour television set (unsure of chassis). This set appears to have been water damaged at some time, but was still working great, until I switched it on yesterday. I was greeted by a bright green flash inside the set, which then shut down. I looked inside and discovered that a PTC thermistor (P801) has fried itself, taking the 250V 3.15A fuse with it.

    I don't know a great deal about posistors, other than their use in the degaussing circuit, and so can't interpret the markings on the top - 14MS 03H4. I have a few spare PTC thermistors kicking around in my workshop, marked as follows:

    M7 MZ73-18ΩM
    14MQ 03L5
    T2 Mz73B-18ΩM
    120M 3003
    07MX KDM61
    A9R0Q 6N

    Would any of these be a suitable replacement? If not, where could I look to find one? I've done a quick search, which yielded very little.

    There is also a small four leg transformer (line filter?) or inductor (it's marked as L801) in the degaussing circuit, so would it be a suspect component?

    Cheers,

    Chris
    (amateur television serviceman)
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,001
    745
    If its in the de-gaussing circuit then omit it and replace the fuse and power it up again,if all is well the screen will be slightly magnetised at the corners, if so then its possibly an 14 ohm type, so replace it with the 18 ohm one to test.

    if it still blows the fuse then its something else.
     
  3. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    give me the exact model number of your set and ill have a look at the schematic and see what type was fitted
     
  4. Chris Ronayne

    Thread Starter New Member

    Mar 11, 2013
    10
    0
    Thank you for the replies!

    Dave, I'll try that. Fingers crossed!

    Sheldons, it is a SAMSUNG TV-516. The code number on the circuit board is: AA41-10657A.

    Chris
     
  5. Chris Ronayne

    Thread Starter New Member

    Mar 11, 2013
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    0
    Dave, the fuse still blew rather violently, so more searching is required! I can't see any other components that are visually faulty, or which could blow the fuse. Any thoughts?

    Chris
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,001
    745
    Well your going to need the circuit of that chassis, possible searches are Lopt, psu, Line output stage transistor.
     
  7. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    im hunting out the service manual-in the meantime check the on off switch for shorts-have a test across the main smoothing cap on the primary side for a low reading,if you have a sc reading check your bridge rectifiers for shorts,chopper transistor for sc etc....on the secondary side do the same test across your ht supply rail and if you have a low reading isolate the line stage and look for faults there. with the line stage isolated load the ht supply with a lamp(when you have a working power supply again )and check you have ht at the correct level.....could you post a picture of the board fitted to this set?
     
  8. Chris Ronayne

    Thread Starter New Member

    Mar 11, 2013
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    0
    Sheldons, I'll take a photo in the daylight tomorrow. Thank you for your help! I'll have to dig out the old set again.

    Chris
     
  9. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    have you not got your camera warmed up yet
     
  10. Chris Ronayne

    Thread Starter New Member

    Mar 11, 2013
    10
    0
    Sheldons, I'll try and get a photo posted soon. I forgot about the thread I posted here!

    Chris
     
  11. sheldons

    Well-Known Member

    Oct 26, 2011
    616
    101
    i now have found the service manual for your model set and power supply wise its pretty straight forward ,heres the smps circuit....
     
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