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No tacho signal - anyone know Igniter resistances?

2K views 14 replies 7 participants last post by  IrlMike 
#1 · (Edited)
I had to put my old gauges back on the bike to get through my bi-yearly inspection, and as I was doing it I blew the rear light fuse.

I may have sent 12volts directly down the tacho signal wire, or accidentally grounded it while fiddling - I'm not sure, but the bottom line is that I now have no signal coming from the Igniter.

Tried wiring both the standard and an aftermarket tacho directly to the blue wire from the igniter, but nothing.

I pulled the Igniter apart and nothing looks burnt, and it looks like there are only 2 resistors that connect the tacho signal (blue) wire to the orange wire (- signal wire to coil #1), and R26 gives me 150k ohm, but R13 shows open circuit.

Click on pic to enlarge....



So my question is does anybody know for sure if R13 is fried, and exactly what value it is supposed to be? It has 621 written on it, at a guess I'd say it was a 620 ohm (62x10?) :dunno

I'm guessing so because it's reading open circuit!
 
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#2 ·
I seem to recall the tacho signal was reduced to about 2/3 of a coil output signal by a simple resistor divider network with values about the 1k mark. Was in a thread somewhere, N5XL I think, maybe in the T3 section?

Is that what you were after Arfer?
 
#3 ·
Sorry to hear of your mishap with the igniter, Arfer. I'll follow this thread since I have a bad tacho, also. The bike I bought for rhe project has had a history of a bad tach.

Possibly, a tech agent at a big dealer, or Triumph itself, could guide you to the proper setting.
 
#4 ·
OK, all fixed :D.

Turns out I was right, that resistor was blown. I found the exact replacement on ebay for 5 bucks (well 50 of the buggers actually lol), ripped the old one out, soldered the new one in and bingo - all working perfectly.

So if anyone needs one of those 620ohm surface mount resistors I have 48 to spare (I damaged one with my first attempt lol).

And here's a pic to prove it...



:doublethumb
 
#7 ·
I'm game for a good challenge, Arfer. My TBird has a non functioning tacho and while I haven't taken it off of the bike and inspected, this sounds like something I'd enjoy doing.

I'd like to pick up a few of those resistors. Three would be a safe measure for the inspiration of Tim, the Tool Man. :) Just kidding..!
 
#5 ·
That's outstanding! What a brilliant repair. I wouldn't have the where-with-all to diagnose a resistor in the ignitor to save my life. So, with everything unplugged, you were able to check resistance across the resistor while it was on the board, without getting any "feedback" from the rest of the board/circuit?
 
#9 ·
Thanks for the kind words Charlie, but it's really not that hard to do. I'm no electronics wiz, just a bodger who happens to have the stupidity to feck things up in the first place, and luckily a few of the right tools to attempt putting it right again :rolleyes:.

Most components can be tested directly inline, especially resistors because the multimeter will measure the path of least resistance - ie the ends of the resistor that you touch to test. This circuit was particularly easy because the Tacho takeoff line (far RHS pin) is only joined to the #1 cylinder -ve signal line (I'm guessing the collector of the #1 transistor) by two of those tiny resistors, and one of them gave the correct reading.

If you're not confident doing that, you could just as easily make an entirely new tacho takeoff line by adding a resistor and capacitor to one of the other transistor's collector lines (or even easier do it externally by attaching it to the actual coil -ve wire), then you'd be reading cylinder 2 or 3's signal instead which makes absolutely no difference to the Tachometer.

Here's the basic circuit diagram for it -



That was my backup plan if it was too complicated or not possible to fix the original takeoff circuit.

Our Igniter circuits don't contain any CMOS chips, so they're not especially sensitive to static electricity (read as some idiot fumbling around with a soldering iron!), but I did use my ESD mat and wristband, and was very careful in that respect, and I always recommend using as much protection as you can.

I could have totally screwed it up, with the upside of that being that I would have had to have bough an Ignitech unit, so I wasn't too scared to give it a go ;).

One thing I did notice is that the soldering on these units is not very good, it hasn't gone properly through the board as it should, especially on the legs of the transistors. That could maybe explain some of the failures of these units we see. But they are relatively easy to repair and the transistors can be swapped out very easily as Ssevvy points out. As long as you can find replacements of course.

Ovni if you want me to send you some resistors just PM me your postal address, that goes for anyone else wanting to give it a go. I've got tons left and I really don't think I'll be needing many more, I can just put some in a normal envelope.
 
#6 ·
Mustang, the Yoda over on the TigerTriple forum, once replaced one of the transistors on his igniter for a few bucks. I built a few amplifiers from kits, and while I am no expert, I think there are probably electronic guys out there that could diagnose one of these pretty easily with the correct gear.
 
#10 ·
I thought it was just a 620/250 ohm divider Arfer, not an RC filter on the board? Which could of course be duplicated outside the board off any coil (signal) terminal?
 
#12 · (Edited)
Yes, you're absolutely right Mike, as I said I'm no electronics expert lol. I was hoping that that filter circuit would do the job, if it won't then please let me know for the sake of keeping the info here realistic.

Curious - if 621 = 62*10 = 620, how do you get 150,000 (150K) from 152? Seems like it should be 15*10**2, or 1500.
It's quite simple really - I messed up and wrote the wrong value :rolleyes:. The resistor in question is actually 1.5kOhm (or so says the "Electrodroid" app on my phone).
 
#14 ·
621=62*10^1= 62*10=620 ohms
152=15*10^2=15*100=1500=1.5k ohms

ok, I get it. The last number is the exponent you put on 10.
 
#15 ·
Arfer, yes, just duplicate the resistor network (whichever values are shown) is the way to go I think. Putting the capacitor in there will introduce a frequency (rpm) variable into the signal amplitude which is probably not desireable.

Useful stuff tho' Arfer, thanks for posting up for us :)
 
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