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Help identifying Component

Discussion in 'General Electronics Discussion' started by Bruno, Feb 1, 2012.

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  1. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    I wondered if anyone could help me identify a component from (what I think is) a switch mode power supply. It is across the incoming mains after some caps and inductors and just before a bridge rectifier and its position on the circuit board is marked "NTR". It is a black disc about 20 mm dia and 4 or 5 mm thick and marked with a symbol looking like an 'e' inside a wide 'u' followed by 20SP and on the next row something looking a bit like a '9' on it's side possibly followed by EI then 005.
    It also has 2 holes blown in it which I'm hoping don't come with new ones.
     

    Attached Files:

  2. GonzoEngineer

    GonzoEngineer

    321
    2
    Dec 2, 2011
    Looks like a Transient Suppressor, or maybe an MOV.

    Also looks like it gave its life so that others may live!
     
  3. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    I have tried some internet searches for Transient Suppressor, or MOV but haven't found anything that seems to relate to the numbers on the blown part.

    This circuit has a FAN7554 Versatile PWM Controller in which I could not find a supply voltage to it so I removed it and powered the circuit which is when the mystery component and the fuse blew, could that just have been a coincidence?
     
  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    That's a 5Ω 7A 20mm Inrush Current / Surge Protector for 220 VAC. It's not placed across, but in series with the mains input.
    The cap's and inductors are just noise filter components.
    If there's a short in the bridge rectifier or any power transistor(s) then this resistor tends to get a hard time, along with the fuse.
    I don't get what you're saying in the last paragraph btw..
     
  5. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Its possible that you apply voltage 220V ac to 110V ac input pwm. That's component was MOV rated 120V.

    You can confirm if this was MOV by tracing etch of 2 ac line input that connects to MOV 2 terminals.
     
  6. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    My apologies, after checking again I find it is in series.
    Is it unusual that a 7A device was damaged when the circuit only had a 1.6A fuse in (which also blew)

    With regard to the second paragraph in my second post, the charger appeared to be partially working initially but was not supplying any output current so I got a datasheet for the FAN7554 IC and could not find a supply to it on pin 7 so removed the IC to try and check further, which is when things started blowing.

    Charger is 230 VAC rated, I'm afraid I don't know what a 'MOV' is.
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    A fuse is not a current limiter. The 7A rating is a hot-state (= lower resistance) continuous rating, not a cold-state (= 5 ohm) rating.
    At the instant before the fuse blew the current was probably 230V / 5 ohm = 46A thus producing 46A * 230V = 10580W in the NTC.

    Removing the IC may have left the power MOSFET Gate floating and thus it could have picked up a charge and become "permanently" conductive.
    The bridge rectifier, the MOSFET, and any low-ohm current sense resistor (in addition to the NTC) may have been damaged by this action.

    If no voltage was present on pin 7 (related to pin 5) then you should check the (100k) resistor between pin 7 and +330V DC. They sometimes break.

    A MOV is a Metal Oxide Varistor, aka VDR, a ceramic material acting sort of like a bipolar zener, to conduct & dissipate overvoltage transients.
     
  8. shrtrnd

    shrtrnd

    3,808
    511
    Jan 15, 2010
    I was thumbing through the newest Newark advertising I got, and I see your device
    in it. It's labelled EPCOS NTC Inrush Current Limiters.
    You should be able to find it on the Newark website now.
     
  9. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    I tried a search for 'newark' but noting looked related to electronics, I am having trouble locating a 7A NTC Thermistor, would a 6A one be OK.

    Checked the MOSFET and it permanently conducting now! - it must be nice when you know what you are doing.

    Would readings of around 0.2 ohms be realistic for the primary windings of the transformer that the MOSFET connect to?
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Just Google Newark Electronics.
    A 6A NTC is close enough, but make sure the resistance is also close to 5Ω.
    Make sure the Gate is discharged (to Source) before you dismiss the MOSFET.
    Yes, the resistance of these switch-mode transformers is very low, even on the primary side. They rarely short out.
     
  11. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Just in case you already have replaced all damaged components and charger still have no or low output. Try to replace filter capacitor of pwm ic ( around 47ufd 25V ) connected to +VCC or pin 7 of pwm ic.
     
  12. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    Thanks for all the help, I will have to find some parts before I can go much further.
    If I leave the MOSFET out, is it OK to bridge the surge protector position to try and check the supply to the FAN7554?
     
  13. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yes, provided you leave the 7554 in place. Otherwise the voltage could get too high on the capacitor connected to pin 7.
    It's better to leave the NTC in place if you are going to apply mains. It'll still work as an inrush current limiter even if it may be off-spec.
    I'd prefer to just Ohm the (100k) resistor though.
     
  14. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    I have checked the resistor and capacitor on pin 7 of the FAN7554 (both OK, 200KΩ & 100µF/35v) and now have 12v across pins 7 & 5 so don't know if I missed this somehow previously.
    I hadn't checked the NTC since I found the holes in it as I assumed it was cream-crackered but it is still reading 7Ω.
    Have ordered new NTC, MOSFET & FAN7554 so will have to wait for the postie now.
     
  15. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Do you have capacitance tester to test 100ufd/35V?

    I've just repair a Forward Converter Power Supply today. It's using Fairchild FPS ic 1M0880. Found 47ufd/25 of its VCC filter capacitor have changed value to 32ufd using my Fluke 79III Multitester. Just replaced with same value. Then PS for PABX working again.:)
    Try replace it. It might save you lot of time and trouble.:)
     
  16. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    Yes, used a meter, I think it was slightly over its stated size, 102µF or something, though I don't know how accurate the meter is.
     
  17. davenn

    davenn Moderator

    13,802
    1,941
    Sep 5, 2009
    thats ok for an electrolytic, they can be as much as 15 - 20% tolerance

    Dave
     
  18. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    I finally got the replacement MOSFET, FAN7554 IC and NTC and nothing has gone bang this time but I just seem to be back where I was at first with the circuit still not giving any output.
    The first part of the circuit is very similar to the FAN7554 Circuit in the data sheet for the IC but the output side is very different, I have been trying to draw the circuit but am having a bit of difficulty with that, it is a Ring Automotive Smartcharge8 battery charger so I tried contacting them and the tech support guy seemed quite helpful initially but finally told me they don't actually manufacture or repair them and would/could not tell me where I might get some info on it.
    As I only know the very basic stuff about electronics is it time to abandon this?
     
  19. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Try measure dc voltage on +VCC or pin7 of FAN7554. You should meaure not less than 15V. FAN7554 will not oscillate if voltage was lower than 15V.. Check starting big resistor ( around 100k 2W ) and if burnt or changed value. If big resistor have correct value. Change filter capacitor connected to pin 7. Even capacitor have passed capacitance test. There might be also a small filter capacitor 0.1 mfd.connected to pin 7 pcb etch .

    WARNING. Big around 2,000 mfd. capacitor after the Bridge rectifier have fatal voltage specially if power supply was turned on and no output. Charge voltage still exist because of no load or pwn ic not functioning. Wait until it was discharged before touching the big resistor 2W. Or you can use your soldering iron as bleeder resistor. Touch the ac plug of soldering iron to terminals of big filter capacitor to discharge. It will take around 30 seconds to completely discharge.
     
    Last edited: Feb 22, 2012
  20. Bruno

    Bruno

    25
    0
    Jun 25, 2011
    Voltage between pins 7 & 5 on FAN7554 was 11v, changed R & C and now get a reading that varies between 12 & 14v but still no output from charger.
     
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