Recently, I burned out the circuitry in a florescent lantern by accidentally reversing the polarity of the volts in. The circuit seems pretty simple, a transformer, 3 resistors, 3 mono capacitors, a 100uf electrolytic capacitor, a 5609 transistor (it exactly says 5609 5C C EBC) and a small diode. I am wondering how I can test the components on this and identify which one to replace. I know the transformer works because I put a power supply on one end and a neon bulb on the other, and the bulb flashed when I added power for a second. I also tested the diode with a digital multimeter and got 620 ohms one way and insulating the other, so i am guessing the diode works. So this leaves the transistor and the capacitors. I am most likely sure that the transistor is the failed component, but I have no idea how to test it, and see what is wrong with it. I am guessing that the transistor is used as an oscillator for the transformer to get the right voltage for the bulbs and thus no oscillation means no light. So how can I test the remaining components (especially the 5609 transistor) so I can see what to buy and replace so I don't have to buy a whole new Lantern.

I know I was stupid messing with it and burning it out, and I should have just kept it to its 6 D battery power supply, but I am only 14 and any information will help!

  • \$\begingroup\$ I tested the resistance from emitter to collector and got ∞ ohms both ways, from collector to base i got 630 ohms one way and 868 ohms the other way, and from emitter to base I got ∞ ohms both ways. \$\endgroup\$ – skyler Nov 12 '12 at 18:23

A good design will have a blocking power Shottky diode to protect the active and polar caps from reverse damage. It looks like your product didn't have one, or possibly you bypassed it inadvertantly with your external DC.

The prefix and suffix to the '5609 are important when you look for a replacement. It is a PNP power switch with linear hFE. Most likely 5A part with 80V rating. The suffix A,B,C are ranked with increased sorted bins of hFE. If not, then no sort.

The transistor can be tested with an ohmmeter as two diodes connected to the base to determine function but sometimes the coil impedance or other circuit loads will affect the result, so removing it is best when in doubt.

Transistors can handle reasonable reverse voltage in fact the Collector-Base is always reverse biased. But the Base-Emitter Veb reverse ratings are much lower.

edit I corrected myself Emitter−Base , Reverse Voltage, VEB = 5 Vdc absolute max on both the 5609 and my suggested replacement.

High eonough to test on an ohmmeter but dont try much more.

However the design must protect the transistor when the inductive load is switched off so that it does not exceed MAX Vce and Veb ( reverse biase mode).

This is a good way to get experience but breaking and then fixing them. That's how I did it at your age. ( and sometimes still do it , heh!)

Here is one possible replacement part.

http://www.onsemi.com/pub_link/Collateral/MJD44H11-D.PDF Specs

I chose one at a higher current rating same voltage , in stock and < $1 @1pc. Depending on your suffix, a better one might have higher beta or hFE. This one is 40 min @ 4A which is not bad.


I agree in that the transistor is most likely the damaged component. One simple way to verify that is to replace it. If the lamp works, then it was the transistor.

You don't say what kind of transistor it is. Different types are tested differently with ohmmeters. For example, to test a NPN first find the base. This will be the one terminal that looks like a diode to the other two. For a power transistor, the collector is the one that will be connected to the case or the heat sink tab. The other is the emitter. For a small signal transistor, just pick E and C arbitrarily for now. Now have the ohmmeter apply a voltage accross C-E. The resistance should read inifinite or very high. Dampen two fingers and put them between C and B. This should make the transistor turn on partially, which should show in a obvious way on the ohmmeter. To verify that amplification is going on, connect the same damp fingers between C and E and see that you get a much smaller response on the ohmmeter. If you're not sure about which is C and E, filp them around and try this test again. You will get somewhat higher gain when C and E are hooked up correctly.

  • \$\begingroup\$ I did specify that the transistor was a 5609 transistor, but maybe that wasn't enough so in an edit, I said that the whole transistor said 5609 5cc ebc \$\endgroup\$ – skyler Nov 12 '12 at 18:54
  • \$\begingroup\$ @skyler: But unless someone just happens to know what a 5609 transistor is, that's not useful. No, I'm not going to guess what manufacturer and chase down a datasheet. That's your job. \$\endgroup\$ – Olin Lathrop Nov 12 '12 at 20:37
  • \$\begingroup\$ So where can I look to find a datasheet \$\endgroup\$ – skyler Nov 15 '12 at 0:55

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