Ignition module

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Dennis, Here is my secret Jonsered parts source, e-mail [email protected] His name is George he has been very helpful in keeping my 49sp's alive. He travels alot for business so be patient. Paul
 
So, does it run yet? I was at Georges house today picking up some spare parts and asked if you had contacted him. He told me you had, and he had the part new.
 
Howdy Dennis,

I perhaps should have mentioned this before, but I had not run your post. I have found that most electronic ignition module problems are not with the module, but rather due to corrosion due to the machine being left out in the weather. The clue is sun bleached castings. To fix; just remove the module, clean up the surfaces that mate to the casting to bare fresh metal, both on the module and on the casting. If there is a ground wire, clean where it also contacts the casting.

What happens is the casting and/or module material corrodes to an invisible oxide layer that insulates. The primary side of the ignition is usually only six volts (remember the pre 67 volkswagen bug problems?) Even a microscopic layer of corrosion/oxide will drop the voltage of the primary well below where the ignition can function. Be sure to disconnect your kill switch before testing any ignition. (The switch can be the problem!)

Some of the old Jonsered's had a capacitance discharge ignition, that if tested with a poor contact at the sparkplug, would destroy the electronics. You need to be careful of this one.
I don't think the 111 - 110 was one of these, I hope!

Any electronic ignition seems very prone to this corrosion problem. The nearer to salt water you live the more likely, and the quicker. I'm in Montana, and I just retrieved a T-20 Sindaiwa, where the problem was corrosion insulation of the trigger module, AND the pickup coil/transformer. Both were "bad", and fixed by an application of emery cloth. The machine had been thrown away and was in the pile to go to the garbage ground! (The plastic top cover was sun bleached beyond recognition of it's original color).

Regards,
Walt Galer
 
Walt,

Good piece of info, I'm off to put some emery cloth to those low voltage ingition wire connections.

Frank
 
Walts right. At Stihls service school 2 weeks ago the service guy was hard on the mechanics for sending so many ignition modules in. He said they tested all 120 of them and 100 of them where ok. Probabably just bad connections like Walt said

John W
 
Good (bad) coils and modules

Hello J.W,
Im Don't think your factory instructor is correct in saying 100 out of 120 coils and/or modules are not defective. I've had 3 of my own personel saws have bad coils /modules. one was a 394 set up to race with. one day it would start . the next day it wouldn't .The other 394 was a woods saw, you could run a tank of gas through it but when you tried to restart it it would not restart. no spark, but the next day it would start just fine but not restart hot. The fix was to install a used 272 coil on them and both saws worked fine. then we replaced both 394 coils and they haven't malfunctioned since. now when husky's quality control section tests these 2 returned coils he's going to test them and they are going to fire cold . then he'll tell the husky rep and the husky service instructor that out of 120 coils 100 were good. its probably more like 20 are good. maybe not even that high, i'll bet all the saws the mechanics replaced the coils on are all running good. the first test on a coil problem is to unhook the on-off switch. i've had corrosion problems on saws but not when they are under 2 years old. the stihl coil problem was on a new 084 racing saw. it made 40-45 cuts before it acted up. it would start but after 5-6 seconds it would die. we figured it was a fuel problem, checked all that out, still wouldnt stay running so we tried a module. they are separate on the 084. no luck so put on a old used coil and it worked fine. Now im sure if stihl tests that coil they will pronounce it just fine because it produces spark for 5-6 seconds so it really was some other problem or we cleaned off that invisable corrision when we had the coil off. but it was a almost new saw so it was not a corrosion problem. I would challenge a statement made by a factory school instructor saying 80 percent of the coil/ modules were good. its just not the case
ken kdhotsaw@ hotmail.com
 
Howdy Ken,

Sorry to have to disagree with you, but I'll bet you live near salt water! Yes, low voltage contact insulating corrosion can occurr in one year. I've seen it even quicker with professional landscapers in Hawaii. Any machine exposed to weather is exposed to this potential problem. Also there is the potential problem of the parts and/or castings having a slight oxidation coating at time of assembly, but everything works fine for a while.

You are not alone in rather loudly disagreeing with this, as it is often a big arguement at service schools. I will agree with you guys on one thing that is not supposed to happen, and that is solid state sealed modules absorbing humidity. I have succeeded in bringing a couple back by leaving them inside on a windowsill in the sun, all summer! The module suppliers absolutely say that it can not be!

I'm surprised, John, that the Stihl service school instructor did not go into detail as to exactly what causes the problem, and instruct to remove, clean, polish contacts, and re-install before giving up on a unit. Stihl considers these so reliable as to offer a lifetime warranty on them, but I don't think they anticipated the strong opinions of the mechanics who really would rather replace parts anyway. You should see the creative writing that goes onto the warranty form!

Incidently, those points replacing little ignition chips have this problem in spades! They are very dependent upon that mounting bolt, or ground wire, ground integrity. Since this is often a cobbled up ground conection, this gives early weakening and then loss of spark. (Remember you have to have blue-white spark, not yellow!)

Regards,
Walt Galer
 
One more thing, Ken:

That hot failure, where the ignition dies only after the machine has come up to good temperature, indeed can be a bad coil. What happens with cheaper made units is that since the windings are only insulated by lacquer, the lacquer can get brittle with age and crack. As things expand with heat, the insulation fails shorting out windings. When cold, everything works fine.

A better quality coil, will have a more durable insulation on the wire windings, and therebye not have the problem.

This is a completely different situation than a completely always-dead ignition.

Regards,
Walt Galer
 
Bad coils/ modules

Hello walt,
sorry walt, but you just aren't right on this arguement.
no, i dont live on the coast. if it was a corrosion or ground problem the coil would work as soon as you removed the capscrews and reinstalled them . thats not what happens. you still have a coil/module that doesn't fire. the manufacturers know the problem is heat related . all ignition systems that use intregated circuitry have heat related problems. I worked on cars for 35 years, when ford came out with electronic ignition in 1975 they had the very same problems. the cars would run fine but when the weather got hot or when the underhood temp. got high or a pickup pulling a horse trailer or fifth- wheel got hot under the hood the electronic componets would fail . by the time the car was towed in it would restart. it was such a problem that when the highway patrol officers would stop to help the stranded motorist if it was a ford they would just get out thier wated bottle and pour it over the ignition module and cool it down so it would start and get them on thier way to the closest shop. Now I have been to many, many factory service schools and had instructors tell us that most electronic ignition modules sent back checked out good but when we replaced the modules the cars ran and the people got on thier way. I'm sure thier are a few older saws that have corrosion and ground problems but most mechanics check that and the kill switch first. on any coil that has a ic circuit module its going to be a heat related problem. the coils/modules returned are not all good maybe 20 percent are good but not 80 percent. your corrison/ground theory just doesn't fly on the newer saws walt
ken
 
Sorry Ken,

I have to disagree with you, except in the case you cite of Ford! I have one. A 1986 Ford Ranger 2.9 liter EFI. (I assume that means Extreem Frustration Included.) The ignition module would fail taking the engine grossly out of time when hot. Problem was the lacquer breakdown between windings, as I previously described. Had nothing to due with the integrated circuit. Cost me $300 to get Ford to solve the problem, and then I had to tell the "technician" what I expected him to find and where it would be located. I made him put the original "brain" back, since he had installed a new one, it was not the problem! (My diagnoses was based on the heat accumulation effect, not having a clue what was really in there).

Just loosening and tightening the bolts may solve a chainsaw ignition problem half of the time, but may not be adequate otherwise. Many units are dependent upon a contact between a tab on the underside of the unit and the casting, not on the bolt. (which is rather insulated by the loc-tite, by the way). Of course, when you change the unit out, and it works, it is natural to assume the original unit was bad. (Post hoc ergo proctor hoc fallacy right?). This is why the manufacturer gets so many good units back on warranty.

Regards,
Walt Galer
 
Wow,
A disagreement with Latin and everything! You guys are
better than cable!
I believe the statement that 100 out of 120 coils that are sent
in under warranty are OK, but not for the arguement that is
ongoing, but due to the fact that there are a whole lot of people
working on small engines that have no clue and are just guessing.
A bad ignition coil is quite rare around here, but we do not
compete on cutting anything, so I cannot comment on the overheating issue. If you have an electronic coil, diagnosis is
quite simple, as to why it failed is beyond our scope and we
should not pretend otherwise.
Fish
 
I have to agree with the fact that alot of ignition units test as good after sent in...John (Walker) ask Pascal how many were tested as good, when he was doing the warranties for Husky...but i do know that some of those ign units did not run when warm...I have had units that will run perfectly, until warm...then they start sputtering and quit....only one thing cures them...a new ignition....
 
guys - i love it!! lol

:D

ok, if i understand the coil thing correctly - you should be able to examine the condition of the insulation by "megging" ie like testing an electrical motor for flux leak - send a large impulse through the coils and if the insulation offers a leak you can see it in the meter....:confused:
 
I can see both sides of this discussion, and I'll say first off that I have absolutely no empirical experience with the things like you guys do so the relative number of good ones to bad ones is beyond my personal experience by a long shot. Secondly, the only Latin that I know is caveat emptor.

Heat related probelms with high tension coils have been around for a long time. These intermittent problems usually manifest themselves as shorted windings in the primary (low voltage, points/module side) due to insulation failure. In many cases, the short manifests itself only after the coil is hot because of expansion.

Perhaps an explanation of how coils work would be of interest here. If it isn't, just flame away!

It's important to understand that the primary is a high current, relatively low voltage environment. I say relatively low voltage because, using a simple breaker point analogy, when the points close, low voltage (from the battery, mag or flywheel mounted charge coils), flows through the primary. This is NOT when the spark jumps the gap. What is happening is that energy is being put into the coil, it's rate determined by the inductance of the primary and the voltage impressed across it. As the points close, the current through the primary will start a zero and linearly ramp up until the points open. Powdered ferrite or a physically gapped core is used here; the energy is actually stored in the physical gap or distributed gap in the ferrite material. When the points open up, this energy has to go somewhere as now you've opened the primary circuit. What happens now is that the coil "unloads" and reverses polarity, sort of like a spring being expanded, then released. The voltage across the primary goes from, say, +6V to -100's of volts during the open circuit condition. This is what they call "back EMF, and it's the same principle as how an electric motor spinning is just like a generator. Because the primary inductance has provided many times the coil charging voltage, the secondary-to-primary turns ratio can be reduced, making a more efficient coil. Peak primary currents in ignition coils are in the neighborhood of maybe 10 Amps. The condenser in parallel with the points limits the peak voltage across them to help keep them from pitting. It acts as a shock absorber to keep arcing down. It also serves to limit the peak voltage across the primary and lengthen the discharge time across the spark plug.


Electronic ignition modules do the same thing as the points, but with a transistor. In this case, the transistor is a switch that's either on (points closed) or off (points closed). The electronics that drive this output transistor can be made to do many things better than a points ignition, such as tayloring the discharge and advancing the timing. 99.9% of the failures of electronic modules in this regard are shorting of the output transistors that drive the coil primary.

Because of the high currents involved in the primary circuit, good grounding and connections are mandatory. A poorly connected electronic module may fail permanently for this reason alone. If a connection is bad on a breaker points ignition, nothing bad happens. If an electronic module isn't connected well, you might blow it.

When the secondary (high voltage, spark plug side) goes, the coil usually ceases to work forever due to carbon tracking. When a secondary looses it's insulation integrity, the high voltage usually arcs across and forms a carbon bridge that effectively shorts out a portion of the secondary. At this time, the heat generated from the arc melts the insulation off adjacent windings, which in turn shorts out more, etc. etc. Secondary DC resistances are usually in the 10's of thousands of Ohms. Carbon tracks are not dead shorts and may be many thousands of Ohms themslves, so "Ohming" a secondary or even hi-potting it may not offer conclusive evidence of failure.

Sparks are interesting things in their own right. We all know what resistance is; well how about a negative resistance? If one increases the voltage across a resistor, the current also increases. If one increases the voltage across a spark plug's gap, the current decreases. This is one principle that allows electronic ignitions to adapt themselves to different conditions inside the combustion chamber by using the current through the spark plug as a sense mechanism. But that's another story.
 
Since points are out of the loop of this discussion, since they
are outdated, what are you saying? That the failure of the
newer electronic ignitions is due to corroded grounds? That
many of the claimed failures of ignitions are correct/incorrect?
Overheating due to poor fin cleaning? I am not trying to
argue,{I never do} but I just wanted to hear your thoughts
on this question.
Fish
 
Howdy Fish,

What I am saying is that the vast majority of ignition failures is due to corrosion under the parts or of the bolts that must conduct to ground.
To fix a dead ignition: disconnect the kill switch and retest. If still dead, remove the ignition parts and clean both the ignition areas that rest on casting or against bolt heads, and the casting the part rests on - to fresh metal. Remount, reset, and test. Over 80% will be mysteriously fixed.

Then there are the cases of failure after warm remaining. These are usually failures in the coil and will only show up when hot. (Well designed equipment will have the ignition with insulator blocks on the bolts, spacing the coil away from the cylinder and allowing liberal air flow). I can't say I've seen trigger module failure just when warm, but I suppose it might be possible, I'm not sure just how. I have seen them absorb moisture, and they are not supposed to.

Regards,
Walt Galer
 
Does anyone have a coil from an older Oleo Mac 999? The one I have has a govenor on the coil, which retards the rpm at about 10,000 rpm. Dozer Dan is building it for me, so we need a coil if you can find one.
Thanks in advance,
John
 
Dbabcock,

Pretty good explaination on the theory. I designed all kinds of wirewound components for TRW during the 70s and 80s including, tuned , audio, pulse, switching mode, power, and high voltage.

As you are well aware many things can happen to chain saw ignitions over time and with temperature (and also from poor connection as Walt said) I would expect that the true percentages slightly favor Walts explanation. Very carefull and time consuming failure analysis would have to be done to know for sure. I don't think the distributors or saw manufacturers would go to the lengths necessary to find the real answeres. The coils manufacturers should be set up to readily run failure analysis on a few returns. A coil Q test with appropriate waveform examination should reveal the problem. Of course, it gets more complicated with the circuitry intigrated into the ignition package nowadays. The mananufacturers failure analysis help could be biased toward not incriminating themselves.

I was once involved where we had manufactured hundreds of coils with significant longitudinal scratches on the secondary #34 nylon poly magnet wire insulation, those went to a marine ingnition application. These were bobbin wound, not layered insulation coils. You can imagine what happened. All it takes in one sharp edge to form on a winding machine eye during production. The first clue is powdered magnet wire insulation building up on the wire guide eye. These defects are not always cought right away by in line production testing methods.
 

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