Replacing 2n3904 with BC337

Discussion in 'General Electronics Chat' started by Feign, Mar 31, 2009.

  1. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
    2
    Short: replacing NPN 2n3904 with BC337 to drive an OMRAM G8P relay

    I have a broken vacuum, the power PCB burnt up a diode(Unknown value) and NPN(2n3904), they controlled the main vac motors relay. I replaced the 2N with the BC device I found in my spare parts. Now the vac "works" but not safely, it powers on but not off correctly.

    The 2N's base is driven by a custom Xilinx chip thru a 470 Ohm resistor. Without modifying the Xilinx firmware what do I need to change?

    I droped out of my Electronics class because I can't read Resistor colorcodes being color-blind. To bad we didn't have all these SMT goodies back then, with thier nice clear but small labeling..

    I "think" I need to loose .3v for the for the new NPN's base, is that correct?

    That would mean adding resistance?

    Question 2: Any guesses at the diode value and orientation?
    It was connected between the Relays coil pins, pins 2 and 6. It was just a spot of carbon before I removed it, so was unreadable.

    The relay switches at 75% and 10% of 12V.

    The Old NPN
    ..

    h
    FE* DC Current Gain
    IC = 0.1 mA VCE = 1 V Min 60
    IC = 1 mA VCE = 1 V Min 80
    IC = 10 mA VCE = 1 V Min 100
    IC = 50 mA VCE = 1 V Min 60
    IC = 100 mA VCE = 1 V Min 30

    All Max 300
    ..​

    The New
    ..
    h


    FE* DC Current Gain
    IC = 100 mA VCE = 1 V
    Min 160 max 250
    ..​

    Relay data sheet:
    http://downloads.components.omron.e...r Relays/Up to 30A/G8P/K108/K108-E2-03A-X.pdf

    NPN datasheets I got off the datasheetcatalog.com web site (I assumed they were from STmicro, the bulk of the chips are..)
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    If the 2N3904 was driving the relay OK, the BC337 should work fine with no other changes. Which relay do you have? This part number is available in a multitude of different voltage ratings.
     
  3. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
    2
    Sorry I thought I put the part number, but I just referenced the voltage. G8P-1A4TP
    Its the 12volt version.

    I made another error, the main microcontroller is a ZiLOG not Xilinx. I am searching for the datasheet for it right now, and not having much success with the zilog website.

    After removing the sticker, "Mercury Ver: 1.0.0" it reads as
    "
    ZiLOG 2155
    8F0223SH0058(Unknown character, Maybe C G or 6, I scratched it with the toothpick or my fingernail removing the sticker)
    0621 1J
    "

    I also just found another 2N3904, it is part of my parallax homework-board set, and I would rather not use it, but I may have damaged the BC337 when I went to verify the voltage the UC was putting to it. Do you think I may have damaged something putting the multimeter to the base pin and ground?

    The Vacuum is not reacting the same way now as it was when I left it to make dinner. It is not triggering the relay, with the rest of the motor drivers.
     
  4. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
    2
    I may have the zilog data sheet downloading, gogo dialup! My dsl should be active in 16 hours 57mins...

    Posibly a encore32 DS0200.. I was unable to find the PCB schematic, unfortunatly, but it is a nice piece of hardware imho. There is a debug port labled "GND, DBG, V33", there maybe an error code waiting to be retrieved. GND connects to ground, DBG to Pin13 of the Zilog and via a "103" smt resistor to V33(tests as 3.3 volts)
     
  5. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
    2
    Excuse the useless postings, definatly not a 256BGA chip. Back to searching.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    As far as the polarity of the diode, the cathode (end with the band) would go to the more positive terminal of the relay's coil connections. You don't want it to conduct when the coil is energized.

    If you've been trying to run it without the diode, you may have fried the new transistor.

    Be aware that the BC337 transistor's pin assignments are different from the 2N3904's.
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    More to the point, both the 2N3904 and the BC337 come in a variety of pinout variations.

    Many 'spare parts' are there because they became suspect a long time ago and that bit was forgotten. Was your BC337 really working, did you check it?

    And yes a BC337 is a more robust transistor than a 2N3904 and should have no trouble handling your relay.
     
    Last edited: Mar 31, 2009
  8. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
    2
    Mutter, stomp, mutter and stomp!

    I was looking at the internal schematic side byside, and would have swore they were identical, double checking and everything, I must have been distracted AND tired. It is most definatly not connected correctly. I spoted it right off now that you mentioned it. I am still (incorrectly) assumeing they are STmicro parts, and using thier datasheets for reference.

    My parts bin is half a working VCR that snapped it's coax input and half a playstation that went airborn because the cd lens got scratched. It WAS a good transistor, before I put it in backwards.

    I still have a pristine 2N3904 from my parallax kit, so hopefully I didn not break anything else. I may have to glue it in deadbug style, my soldering skills are a bit rusty and the board is going to show it when I remove the one I put in..

    Nope did not test the BC337, I'll do a search for NPN Transistor testing and start a new thread if I can't find one.

    I'll do a "Putting it all Together, Hoover vacuum repair" thread if and when I come to a final conclusion. Don't answer the test here, some of us are search impaired and might miss it..
     
  9. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
    2
    Last edited: Mar 31, 2009
  10. Feign

    Thread Starter Active Member

    Mar 30, 2009
    50
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