Hi everyone. I hope you are all well during the strange times!

I have been browsing these forums for quite a while but I have never actually posted before. (I wasn’t a registered  member until my registration was approved today!)

I have owned a 1992 Suzuki savage for quite a few years but unfortunately it has been off the road for several years due to electrical gremlins. I was hoping that the community here may be able to help me get to the bottom of it!

The bike is a bobber and has had the wiring cut and simplified. This was done previously to my ownership.

I am having trouble with the ignition system on the bike. I currently have no spark at all. (But using an inline spark plug light I do have a faint flash of light as I crank the bike)

I am going to write the history of the problem in chronological order to try and make things clear:

1 - Bike was running fine, starting and running perfectly.
2 - During the winter the battery went flat and the battery was replaced with a new one as the battery was very old. When the battery was replaced I caused an accidental short within the battery box. I am not sure what shorted as the wiring inside my battery box is quite tight.
3 - The bike would not start and had no spark.
4 - I tested all of the ignition system components as per the Suzuki service manual:

Ignition coil primary coil - 1 ohm
Secondary coil - 20k ohm

( I noticed that the HT lead has a spark plug cap on it which has a 10k ohm resistor in it) so secondary coil resistance is actually 10k ohm.

resistance across pickup coil - 208 ohm

battery voltage 12.8v

12.2v when cranking

5 - from here I came to the conclusion that the Igniter (TCI) box must be causing the issue. I opened up the TCI box and found the transistor was burnt out.

6 - I managed to find a used TCI box on ebay with the same part number 32900-24B00

7 - Fitted used TCI box. Bike had a spark and started. I tried to rev the bike and the bike stalled. Bike stalled due to lack of fuel.

8 - At this point ignition is still ON. I went to fill the bike up with a jerry can of fuel. During this time (2 mins or less) I noticed a burning smell and found that the transistor had burnt out again.

I have now read on the forum that leaving your ignition on without the bike running is a bad idea as this can happen. But would this have happened in the 2 mins it would have taken to fill the bike up with fuel?

I have managed to source some replacement transistors to solder onto the board (Fuji D1071)

I am apprehensive to install the new transistor if something else in the circuit is causing the issue of burning the transistor out.

I have also just purchased a voltage regulator / rectifier as the one on the bike was looking old and a replacement was fairly cheap.

I have checked all of the wiring and I couldn’t find any shorts between wiring or to the frame so,

My questions are:

Could the pickup coil cause the transistor in the TCI to burn out?

Could a faulty ignition coil cause the transistor in the TCI to bun out?

Is there anything else I should be looking at before I replace the transistor again?

Many thanks and sorry for the long winded question! Looking forward to getting the bike back on the road soon!

Cheers,

Tom  

Thanks for the message Verslagen.

So I have now replaced the ignition coil. I noticed that when the ignition coil that was fitted was lightly heated with a heat gun that the resistance would quickly drop to 0 ohms.

I replaced the coil with a brand new aftermarket coil from eBay. The resistance of the new coil shows as 1.5 ohms on the primary coil which is within the spec of the service manual.

I have also replaced the transistor on the board with a new D1071.

Disappointingly - I still have no spark. With a spark plug tester between the HT lead and the plug I still see a faint flash when cranking but absolutely no spark.

I don't appear to have any shorts on the wires leading up to the coil. I see 6amps on the primary coil with a DC clamp meter.

I notice that the transistor gets extremly hot within seconds of the key being turned on.

I have attatched a drawing of the ignition circuit which shows that the base of the transistor is controlled by the TCI modules and the collector pulses the ignition coil.

I am now wondering if there could be other failed components on the TCI module circuit board?

To be honest I am really scratching my head. I would be willing to buy another TCI if there was one available for sale.

Any suggestions would be very much appreciated. I have spent far too many hours trying to diagnose what is seemingly a simple fault!

Many thanks!!

according to the datasheet...
Quote:


you need to get the temperature down or the current down or get a higher watt IC.

Thanks kamelryttarn and Verslagen,

This is still me (Cornish Savage) but on my dads old user account. For some reason it wont let me log into my own account and wont let me reset my password... Anyway.

Kamelryttarn, that is interesting that you have 3.5ohms on your primary coil. I wonder if using this aftermarket (Cheap) ignition coil with 1.5ohms is causing my problems with burning the transistors. It would make sense that this could be the problem.

By my calculations using ohms law, 1.5 ohms of resistance at 12v would give 8 amps of current

On your primary coil with 3.5 ohms of resistance, at 12v you would only see 3.4 amps of current.

Going by Verslagens datasheet, it would appear that my coil is overloading the transistor which has a max current of 6A.


kamelryttarn: there are several capacitors on the circuit board and lots of resistors and diodes/zener diodes and a couple of amplifiers. I do not have a schematic of the board so it is hard to identify exactly what each part of the circuit does what. It would be amazing if someone did have a schematic of the board.

I have managed to buy another TCI board from the states which is being shipped over to me here in the UK. In the meantime I will purchase an OEM coil and maybe try replacing the transistor again....

I have been reading on various webpages and forums and I have found a guy that recommends replacing the transistor for a Bosch BIP373. They apparently come in the same form factor and are very rugged, with built-in over-voltage and over-temp protection. If it starts to cook, it simply shuts down.

Unfortunately these transistors are not easily available in the UK. Has anyone with an LS650 managed to upgrade the transistor on the board with a more modern variant?

Cheers!

cornishgonzo wrote on 10/30/20 at 11:52:39:

Thanks kamelryttarn and Verslagen,

kamelryttarn: there are several capacitors on the circuit board and lots of resistors and diodes/zener diodes and a couple of amplifiers. I do not have a schematic of the board so it is hard to identify exactly what each part of the circuit does what. It would be amazing if someone did have a schematic of the board.

I have managed to buy another TCI board from the states which is being shipped over to me here in the UK. In the meantime I will purchase an OEM coil and maybe try replacing the transistor again....

I have been reading on various webpages and forums and I have found a guy that recommends replacing the transistor for a Bosch BIP373. They apparently come in the same form factor and are very rugged, with built-in over-voltage and over-temp protection. If it starts to cook, it simply shuts down.

Cheers!

Could you try and snap some pictures of the board? The capacitor I am most interested in should be connected in parallell with the transistor (between the collector and emitter).

And heres the underside

If you have it torn down to that level, may as well replace the electrolytic caps.  They in many things I repair (radios)  is what I usually suspect  goes wrong.  Get quality ones with high temp rating, long service life, correct voltage,   uF, and watch lead distance.

I used my LCR meter to measure the capacitance in the CDI box on the pins that connect to the ignition coil and got around 330pF.

Regarding the transistor I believe you can replace it with almost any NPN Darlington transistor you can find that has similar or better specs. I would give the following a try

https://www.onsemi.com/pub/Collateral/MJE5740-D.PDF