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electronics type question - transistors and what they do?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by lotus7, Jul 14, 2006.

  1. Can someone with better electronics kung fu please help?

    I have a particular transistor in my bike. It appears the switch functionality works fine, however the output is not what I expected:

    1: show a open circuit (this occurs correctly).
    2: show a given resistor output (instead I see a closed circuit).

    It was suggested to me that the transitor only shows the resistor output for a very brief moment and then closes the circuit, and that this is too fast to measure, thus I am seeing the closed circuit when I attempt to measure in the switched condition.

    Alternatively, I think perhaps the resistor has blown - but since its a sealed unit I cannot easily check.

    So... any help welcomed!
  2. Andrew, can you be more specific?

    If this is a sealed ignition unit, there may be many more things at play.

    From my old electrical principles days (a long long time ago), we didn't measure resistance across transistors the way that you seem to be doing.
  3. This is a very simple circuit - part of a "smart tre" that goes between the gear position sensor and the ecu. Basically, the tre is meant to convert all gears other than neutral into 5th gear. If I measure the output from the stock sensor in 5th gear I can see 6800 ohm consistently as expected. When the tre is inbetween and the bike is in gear all I see is a closed circuit.

    Here is a very basic circuit diagram to explain - if that helps:


    The tre is the box at the bottom...
  4. Edit: cancel that, youve posted more info while I was posting :)

    Yeah sorry, Im lost, need more info. :?

    Is the test your doing similar to this? (more the analogue one)
  5. From my basic understanding of electronics, a transistor has to be removed from the circuit to be tested. In my experience this usually b#ggers them. So read the numbers, find an electronics store & solder in a new one. Only a couple of dollars so no real biggie.
    Think of a transistor as a tiny relay. A very small input signal causes it to switch a higher current to on.
  6. mmm, not sure of the diagram is correct. It would help if I knew what the ecu expects to see from the gps.

    All a transistor circuit like this does is function as a switch or a small current amplifier.

    The way you would normally measure if a transistor circuit was working would be to measure voltage (at the emiter from memory) or current flow. What I imagine the 'tre' unit is doing is just presenting to the ecu the voltage it expects to see from the gps in 5th or 6th.

    A very simple circuit and easy to troubleshoot. However, rather than do that, I know that Johnny O has fitted a similar unit to his K6. He might have some tips if you are having problems.

    Some tutorials for you:




    It's sad to think that when I was an apprentice, I knew all of this (and way way much more) like the back of my hand.
  7. It should be impossible to measure "closed circuit" (I asume you mean "short circuit" which is 0 ohms, closed circuit just means theres a conection of any resistance)
    Should be impossible for that module to measure less then 15k.

    Do you have the module disconnected from the bike? Otherwise the tests wont really work.
  8. If you look at the diagram posted, im not measuring directly across the transistor - im measuring the output to the plugs. When in neutral I get an open circuit - exactly like stock. When in gear I see a closed circuit - im expecting it to be 6.8k ohm (note that the circuit diagram shown has a 15k ohm resistor - should be 6.8k I just couldnt find a predrawn one with the right one in it).

    So, is it showing 6.8k for a brief moment then closing the circuit (and thats how a transistor works?!) or is something amiss here?

    The only reason I payed for one was I couldnt find a supplier for the suzuki connectors. By having them its very easy to instal or remove at whim.
  9. Ok, here is a clearer diagram which shows the workings of the stock gear position sensor..


    again, the tre shown here is emulating 6th gear instead of 5th which mine *should* be doing...

    When I remove the TRE and measure the output of the gear position sensor I get:

    neutral: open circuit
    1: 560
    2: 830
    3: 1.5k
    4: 2.7k
    5: 6.8k
    6: 15k

    when I put the tre in place (it sits between the gear position sensor and the ecu) I get:

    neutral: open circuit
    1: closed (i.e. short circuit)
    2: closed (i.e. short circuit)
    3: closed (i.e. short circuit)
    4: closed (i.e. short circuit)
    5: closed (i.e. short circuit)
    6: closed (i.e. short circuit)

    Im expecting to see:

    neutral: open circuit
    1: 6.8k
    2: 6.8k
    3: 6.8k
    4: 6.8k
    5: 6.8k
    6: 6.8k

    Does that help explain its function better?
  10. Even more confused.

    With a switching voltage applied to the base (the blue wire in your picture) at the collector (the red) I would expect to see at best the 6.8K resistance.

    With no switching voltage, I would expect to see an open circuit. What you might not be taking into account is how the GPS and ECU interact. Basically you are inserting the Tre unit into the ECU circuitry. There could be any number of circuit permutations on the other side of plug. Hence, we need to know what the 'expected' values are for both the Tre and the standard unit.

    Or give John a call!

    EDIT: Seen your post. Analysing...
  11. cejay - thats exactly what im expecting, just not what im seeing...

    No switching voltage means neutral - which is open circuit. Johnny O didnt fit his TRE since it disabled the stock gear indicator and last I heard was selling it. I undertstand the concepts behind what the tre is meant to be doing, and why you want it.

    My question really is - with the switching voltage, should I continue to see 6.8k ohm or will it only be momentary (i.e. so fast I cannot measure it)? This is what a manufacturer of tre's suggested - but that confuses me as to how the ecu will interact with a closed circuit - in the stock situation this would mean I was "not in a gear". I half expect the ecu to see this and run in a "limp home" mode...
  12. Ok.

    It works thus:

    When in neutral, there is no voltage applied to the base. With no voltage, there is no path to ground, therefore there is no voltage being developed at the ECU. Once a a gear is selected the grounding effect at the base is removed and a voltage is applied. This opens the circuit and a path to ground is now available. This brings into play the 6.8k resistor, which, combined with the 1k resistor develops a known voltage at the ECU.

    To test the circuit.

    Measure the voltage at the blue wire (it looks blue to me) at neutral and in gear. I would expect to see a voltage there in gear and a direct earth in neutral.

    If you get the expected values, then measure the voltage at the red wire in the same circumstances. If you see no voltage at the red wire, the unit is defective. Unless you can open it, you cannot test further.

    It's unlikely the resistors are blown, unless they are crappy quality. Much more likely there is a break in a wire or the transistor has failed. Seeing as it's just a simple switching transistor, you should be able to buy a new one for pennies. The biggest problem you might find is that you have to buy 10 or a 100 of them!
  13. Don't measure resistance, measure voltage. That's what the ECU is expecting to see.

    On that specific point, they are talking nonsense. My understanding is that the GPS just tells the ECU that you are in a specific gear and to use a specific map for that gear. In 5 and above, you get full power. Why they change the resistance for each gear is strange, I assumed there was a 'Full Power' and 'Less than full power' difference, but obviously not.
  14. Ok, sounds like its defective. Bugger. Well, easy enough to get it replaced... but this makes me quite curious - Suzuki ecu runs different ignition maps for different gears - given im basically not in a recognized gear, I wonder what its doing... certainly seems to "run" fine, and no error conditions come up on the dash. Will see what happens eh.
  15. Remember this is my take on the matter and might not be the opinion of management.. :)
  16. Disclaimer duly noted :wink:

    Now, if only we could reprogram the ignition maps we wouldnt need the tre in the first place... time to do some hunting!
  17. I'd say it actually thinks you are in neutral. Therefore, probably the same map as one of the other gears, maybe 1st?
  18. Ohm meters arent supposed to be used with power applied, its can make them read garbage.

    Measure voltage at red wire and ground.

    Neutral I would expect to see 5v
    in gear I would expect 4.4v (if N measured 5.2 then add the .2 to that, or subtract if it was less then 5)

    If in gear it gives 0.7v then there is no resistor, which would explain the short your meter is reading.
    But if its the 4.4v then your ohmmeter is just going spastic because of the external voltage, the resistor is there or you would bave 0.7v

    Sounds like the transistors ok anyway.

    Otherwise you could disconect (or cut) the red wire to take any voltage off it. But I recomend trying voltage measurements.
  19. My take on the neutral gear position is that there should be a floating voltage at the ecu. From the diagram, when neutral is selected, the base of the transistor is ground. The transistor is off and the collector voltage should be floating. But I am happy to be wrong. I agree, the voltage at the ecu with a voltage applied at the base should be 4.4 (ish).
  20. OK just to be pedantic, the circuit has to be drawn incorrectly as the blue wire is not connected to any of the resistors attached to the gear switch, therefore you will be seen as either in neutral or no gear, which will have the same effect to the ECU. ie the transistor will be turned off and no current flow, and +5V will appear on the A/D.

    For the GPS switch to work as a momentary action then either: the switch works only when you actually change gears (this makes no real sense), or there is other circuitry missing off the diagram (this is possible).

    Now as to the actual workings:

    The basic design seems to be the transistor is working as a variable resistor and not as a switch. This gives a voltage divider function to the analog to digital (A/D) input that varies dependent on gear selection.

    So if you measure the voltage at the ECU input you should get a different voltage with each gear, and neutral should be +5V

    What the actual voltages will be, depends on how the GPS resistors are connected to the transistor, and the type of transistor in use, and if there is more circuitry than shown.