Care and Repair of your TCI

This is for XJers like me who when they look at anything electrical on the bike have their eyes glaze over with a total lack of knowledge of how it all works...

What is the TCI?

It's the heart of your XJ. It's responsible for ensuring your spark plugs spark at just the right moment at just the right RPM. The "TCI" (Transistor Controlled Ignition) usually sits under or to the side of the seat area and is a little black box around 4" x 3" approx. and should have some alpha numerical markings on the top which designate whether it's for your XJ550/750/900 etc. Generally, any problems can be related to a bad solder joint cracked with age or a blown component.

About 12 months after the acquisition of my XJ900 I was experiencing problems with erratic running of the engine the cause of which was hard to pin down (it would start and go nicely and then for no reason cut out for a second or two and then fire up again - really exciting as you're leaning into a corner!!!).

And I tested with a meter every related electrical component on the bike and all seemed good but could not find a way of testing the TCI (maybe because there is no fool proof method of doing so). I was lucky to obtain the loan of a known working TCI module for a 900 and as soon as I hooked it up my erratic running problems disappeared. Worth noting, I just received my copy of the XJ CD and it has a good section on the TCI unit...and having received the XJ CD I can highly recommend that anyone who works on their bike spend the $10 or so to get a copy; it will save you both grief and much $$$ in understanding and repairing/servicing your bike.

TCI's are repairable and via the resources available through this great XJ site one of our own can help you with your TCI problems. I sent mine to fellow XJer Robert in California, who was able to diagnose and repair the faulty component(s). Got it back, plugged it in and...good as new.

If your bike is running erratically (or not at all) and you've tested all other avenues such as fuel flow/carbs and meter tested battery/regulator/rectifier/alternator etc., then it may be worth chatting to Robert to see if your TCI is messing with your mind...

Remember, your TCI could be 25 to 30 years old and depending on exposure to the elements over the years components have aged at various rates and solder joints might have hairline cracks perhaps momentarily disrupting power/spark to the engine.

If you think you have TCI problems get back to me or Robert for more information.

 

I'd consider the engine itself to be the heart of the machine... IMHO, the TCI unit would be more like the brain.

Kinda like the distributor system on an older car.

Courtesy of Dave Jackson from New Zealand. The likely culprit is either one or more of the six electrolytic capacitors that inhabit the circuit board, a bad solder joint, or both. This happened to me a few years back with my 750, when it was cutting out while riding like I'd hit the kill switch. After swapping the capacitors out and touching up the solder joints, it's been rock solid ever since.

Like you say, it's repairable -- if I can do it, so can anyone.

 

Often, if the bike stops running when hot (or hard restarting after a quick stop), but on cooling starts okay, that is also a point toward this wonderful component...

 

RedCentre003's TCI had a bad switching transistor, I replaced it along with all of the capacitors. Should be good for another 20 years. I am heartened that so many of you have been successful in repairing your units. I am still overhauling units so if anyone else needs a repair or a capacitor refresh, let me know...
I would also like to gather up a dead board or two so I can map out the boards for the respective units and have new ones made (the more I buy, the cheaper the cost) to repair damaged boards. I will accept donated dead TCI's for this effort.

 

Could you send me a little more info on the cost and such on repairing TCI. Also, i have an 80 xs1100. Can you do these units as well, plus CDI units?

 

Lemme do some digging... I remember taking pictures of mine when it was apart, but I don't know if I still have them or not.

 

You'd probably be better to PM robert directly about that chvbob.

 

I don't know anything about the 1100 units or CDIs but I would be willing to hack at anything, electronics is electronics regardless of manufacture or year. I have yet to figure out how to get the sealed units (out of 85+ 700s and the like) open in a non-destructive way so I'm still working on those.

 

Robert: I found the pictures I was looking for, but they only show the component side of the board, and I don't think they're as detailed as you'd like. I can still fling them in your direction if you're so inclined.

 

Quick question here about the TCI. (I have always referred to them as the CDI box. Taken from the old dirt bikes & snowmobiles.)

Are they computer controllable, or are they just an electronic distributor. I have seen a few after market ones that claim to produce a better power curve? Can they be reprogrammed? I have been out of the street bike scene for quite some time now, but I see them on TV plugging the newer bikes into a computer to reprogram them.

 

I don't believe these have any upgradable "code" in them. I'd expect the timing advance curves to be burned into a mask ROM microcontroller of some sort. But Robert can probably say more about that.

They're also not even "electronic distributors.", as distributors switch the high voltage spark from one plug to another. TCI is much more comparable to the TFI module in Ford ignition systems, in that it gets a trigger signal and uses that to fire a coil. TCI, though, contains two separate ignition circuits; it gets signals from two crank pickups under the left cover, applies RPM-based timing advance, and charges and fires the two coils using included ignition driver transistors.

TCI stands for transistor controlled ignition, it uses transistors instead of points to dwell the coils, then opens the transistors to fire them. CDI is capacitive discharge ignition, which charges up a capacitor, then discharges it into the coil, which acts to step up the voltage to fire the plug. TCI coils run on 12V. CDI coils run on about 200V.

 

Just an electronic distributor, is my understanding.

Not to my knowledge; these bikes predate the widespread use of fuel injection (although there was a Japan home-market model that was injected). If one wants to fab their own injection setup, as has been done, I would think it would be feasible.

 

No, they're not. There's nothing over 12V in a TCI. It could be called an ignition module, or an ignitor, but it's not a distributor.

 

Robert, this link talks about getting into epoxy sealed units
http://www.perthstreetbikes.com/forum/f ... ble-86757/

This link is a full on TCI geek link! 8) (probably owned by somebody on this site :lol: )

http://www.jetav8r.com/Vision/IgnitionFAQ.html

 

Not in the strictest sense, granted -- you've already gone over the highlights, so I won't rehash. However, I'm hoping that calling it a distributor, while technically inaccurate, illustrates that it's not user-programmable.

 

SQL, VERY nicely explained, I could not have done better. You are correct, it is not a distributor. It merely acts as a high current switch.
It has a burned IC chip and is not reprogrammable.
Kevin, the newer aftermarkets have the advantage of being able to flash in newer or modified curve programs. You can wander down that path but it means you need to understand how to wire it in. One wire out of place could fry the new unit. Other than that, their cost is quite high so I'd do a lot of research on which ones would be compatible with our "lost spark" system.
Adrian, Thanks for the links, I've never seen the first but I've been in touch with jetav8r for technical discussions in the past. Good stuff for someone interested in learning just what is going on in there and/or wanting to repair their unit!