EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: jerryk on December 03, 2020, 01:56:09 am
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This board is off a jump pack I'm trying to repair.
The marking are B139E with dots above and below the marking. Any help on what this is and how to interpret the dots in this configuration is appreciated.
Also I have an SMD diode on the same board marking of S16G in an SOD 323 package that I need to identify.
Thanks in advance - Jerry
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2SB139?
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Thanks but I can't find a 2SB139 anywhere in the searches that I've tried. Any tips on where to find it?
What I have tried is to assume there is date code in the number and used B1 and B13 as a possible marking scheme. Looking at the caxapa site (http://caxapa.ru/thumbs/588912/smd-codes.pdf) the closest possibility is the 2SC3739-13 (SOT 23) or 2SC4173-13 (SOT 323). But I can't locate either of those if they are in fact what I need to replace that component.
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If you trace the circuit in that area, then that should at least tell you whether it is an NPN or PNP BJT, or maybe a MOSFET.
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Assuming pin 1 is the base it goes through a 2K series resistor to the collector of an NPN transistor. When I test the collector (pin 3) and emitter (pin 2) in diode test mode with positive terminal on pin 3 I get a forward voltage of .624v. No other junction tests show any forward voltage. Holding the positive terminal of the multimeter on pin 3 then touching (momentarily) the negative terminal to pin 1 causes pin 2 and pin 3 to have continuity for a few seconds and the returns to open circuit. Keep in mind I'm assuming base, emitter, collector for pin 1,2,3.
Might it be a p channel mosfet?
Hope this info helps.
Jerry
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I pulled it out of circuit and by digging into the side of the broken lead with a razor blade was able to get a reading on my DCA75 as to what it is. The output of the component test is in the attached images. If there are any suggestions for a P channel mosfet might work as a substitute that would be great.
Thanks - Jerry
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Is this MOSFET configured as a high side switch? Does it switch the BAT input?
If it is working, then why do you want to replace it?
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My guess it that it's the switch in the so called boost circuit. It's in that area and from other jump pacs that I have worked on there is a minimum voltage required returning from the jumper cables in order to transfer the power to jumper relays. This is around 9 volts on other devices I have worked on. Absent that voltage you can hit a boost button that will override this safety for a minute or so and jump a dead or sub 9 volt battery. The gate of the mosfet traces back to one of the micro controller pins.
Again just a guess as I have not sketched this circuit out.
I'm replacing the mosfet only because the drain pin was corroded and snapped of completely. That why I had to cut into to side of the mosfet to get enough material to connect the third lead of the Peak component tester. Otherwise I'd be happy to leave it be. Lots of corrosion on the board and many dissolved leads from various IC's.
Right now I'm just fixing it out of pure spite to see if I can make it work. For me it's good practice on salvaging the old pads and the like. I do think saving it is possible as I think the micro controller is alive still.
I never can seem to make the output of that DCA75 match even a known components datasheet unless it's a simple zener. Hence, the asking for a favor from the more experienced in translating the DCA75 output in those photos to an available components datasheet. Otherwise I'll do my best in picking one.
Thanks for your input and help.
Jerry
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Could "S16G" be a 16V TVS diode? A full photo might help.
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This is one I took out of circuit and tested with the DCA75. I shows it as a Diode junction with Vf of 6.23V. There are several of these on this board.
I did find this datasheet (https://www.alldatasheet.com/datasheet-pdf/pdf/984568/YANGJIE/S16.html?) that seems to match it. The substitute I have in my cart at Mouser is
a PMEG6010CEJ,115 (https://www.mouser.com/ProductDetail/771-PMEG6010CEJ-T-R). Not sure if it's a correct or best choice.
Edited - to add other photos of circuit board as a whole. Mosfet in question is Q4. S3 is the boost switch I referred to above.
Jerry
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Just wanted to follow up and say that this unit is repaired and working correctly. It had a lot more damage than I originally thought. It took a couple of tries as I ended up causing a bad solder joint on the ground pin of the new LM393 that I installed as one of a many parts replacements on this board. The original mosfet in question labeled B139E was replaced with a DMP2305U and it's working fine. The S16 diodes were replaced with PMEG6010.
I have attached a video of the repair description and a photo of the final assembly of the jump pack.
Finally, I wanted to say that help that you guys provide on this forum goes a long way on projects like this. I sure do appreciate it.
Jerry
https://youtu.be/Vs_xF-iRTo4 (https://youtu.be/Vs_xF-iRTo4)