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Capacitor replacement

Former Member

Hello everyone!

I would need your help solving a little problem where I am not sure of the value of a capacitor that I need to replace.

I have never seen a capacitor like this one (yep, I'm a noob) so I searched online for some info and I though I could read it's value...the problem is that when I desoldered it from the board I noticed that on the other side it had other things written that, to my little knowledge, suggest a different value. Here are the pictures:

 

image

From this one I read that the precision is B, and the value is 4.1 uF with max 400v. The rest of the letters I have no idea what they mean.

image

From this one I read that it is a 4,7 pF capacitor and the precision is M. The rest I do not understand.

 

What I would really like to know is what the actual value of the capacitor is and if possible, what the various things on both sides mean so that in the future I will be able to read them.

Thank you very much in advance

  • 0 in reply to Former Member

    Hi Francesco,

    Your transistor number does cross to an NPN deflection / flyback transistor. How are you determining the polarity of your test leads on your Ohm meter? Several of my meters have the positive voltage on the black lead of the Ohm meter. Confusing but for whatever reason this is the way they were designed. Typically these transistors fail in a shorted condition. If you do not have a short between any of the leads it may not be the transistor.

    John

  • 0 in reply to mcb1

    Ok, thank you very much...by adding the "2S" in front I was able to find a lot of information on the transistor!

  • 0 in reply to jw0752

    The multimeter should be "regular" with red as positive and black as negative because all other readings suggest so and I was also able to power up an LED with the diode testing mode and that further suggested what the polarities are. Now, assuming it is a NPN transistor as the datasheets say, I built a tiny circuit giving +5volts to the Collector, ground to the emitter and when I put something around +3 volts on the Base the current went through (I powered an LED). I also am pretty sure of which is base, which collector and which emitter because they are printed on the board. The transistor seems to work fine with low voltages and currents, I don't know if it may behave differently when those currents are increased...this to me suggests that the problem is elsewhere.

     

     

    Ok, I just did another test...this time I assumed it was a PNP transistor. I connected +5v to the emitter, ground to the base and current went out the collector to power an LED. At this point I figured something was wrong so I disconnected ground from the base and it still powered the LED...I am afraid either I do not understand transistors that much (very very possible) or the transistor is working in weird ways

  • 0 in reply to Former Member

    Francesco

    Can you confirm what pins are 1, 2 and 3 in your testing.

    http://www.svntc.com/TPDF/2428.pdf

    Also can you confirm what the 1, 431 and 40 reading is (Ohms, diode test or ??)

     

     

    One of the faults that can show is a collector to base short, and the reading of 40 between 1 and 3 doesn't tie in with the other readings.

    I would expect a +ve on the base will conduct to the emitter.

    I also expect a +ve on the emitter will conduct to the collector (using the protection diode)

     

    Mark

  • 0 in reply to mcb1

    Hi Mark,

    pin 1 is base, pin 2 is collector and pin 3 is emitter, just as in the pdf you linked.

    The readings are from the diode test.

  • 0 in reply to Former Member

    Francesco

    Thanks for the confirmation.

    I assume when you use your meter on diode test with nothing connected it will read 1.

    if so ...

    this is the representing the forward bias voltage of the diode under test, which is usually around 0.4v on these testers.

     

    Using this it appears the transistor is working fine.

    1 and 3 = 0.040 which is the resistor

    -ve on 2 and +ve on 3 = .431 which is the reverse bias diode

    +ve on 1 and -ve on 2 = .406 which is the reistor and diode in series plus the base junction conducting and possibly the C-E also conducting slightly.

     

     

     

    One thing an older guy at work taught me for testing switchmode supplies.  image

    Make up a lead with a lamp in series in the phase wire.

    If you use a 100w lamp and the switchmode has a short, it will light the lamp instead of making a big bang.

    If the 100w lamp is not enough use two or a 150w lamp.

     

    Mark