330 electronic ignition

[dynodave]

I got my 330 seemingly running OK. However the guy who gave me the saw said it had an EI problem. Well it seemed to run sweet and I though he was mistaken. However after starting to use the saw after a few big cuts it would die instantly. After resting or cooling it would fire up and go again for a few minutes and die again.
I finally accept that I have a bad EI pn A94361.
I bought an ebay NOS one and will give that a shot. I will try and demanufacture the old one and do an autopsy and attempted repair If I can identify the intermittent component.

[sweepleader]

I have wondered about those units, if you removed the electronic stuff and left just the coil, could you then install a chip like you can in place of points and get it to work? Some have said that it is possible on some models where both type if ignition were offered that you could install a points coil and a chip in place of an electronic unit but what about those that no points were ever offered? Let us know how that autopsy goes and what you find in there.
Dan

[dynodave]

Defining the problem will decide what can be a possible cure. Is it a hall type trigger part (input) or output transistor that turn on and off the coil. I would think you would have to partially demanufacture the EI unit to get at the coil end of the primary wire to hook up an aftermarket trigger/coil driver.

[sweepleader]

I am no expert, but I saw one on TV once! Anyway, I was just wondering since the aftermarket chips get away without any timing signal other than the flywheel magnet, perhaps the factory combined EI would do the same. Perhaps that is where the aftermarket got the idea. I am sure you are correct when you speculate that the coil primary connection would have to be uncovered to connect the chip. I just wondered if indeed the coil itself was the same as a points unit, with the addition of a factory "chip" embedded in the potted unit. You sound like you understand the electronics and could tell what you were looking at if the potting was removed, I could not. Since others report success replacing the EI with a points type coil and a chip, I suspect that the magnet/timing is the same in both units. That might indicate that a Hall Effect transistor was not needed and that lead me to suspect that the coil might be the same too. Just curious and wondering but I am not really able to offer and brilliant insight. Perhaps if you could identify the bad component it could be replaced and the EI repaired. A place where I used to work could dissolve the potting out of a sealed unit so it could be repaired, I do not know how they did it without melting the electronics inside.
Dan

[dynodave]

A few days ago, I finally put in the new $40 EBAY EI. Yesterday I cut a big pile of oak (long bed pick up load). The 330 ran flawless until the new chain went dull, and my second chain was also dull. My friend with his husky 55 took over but was very positively impressed with the homelite, since he tried both saws. Now I will disect the old EI. Let you know what I find....

[sweepleader]

Hey, glad to hear it runs well, I will be interested to hear what you find in the EI.

[dynodave]

Have dissected the 330EI/coil. Taken a few annotated pix.
limitations of my cheap camera are obvious but my eyes can easily see whats going on here...
fix would be very difficult but swapping other EI on to another core lamination may be not to difficult.
330EI2link
330EIbottom
1. There is a typical high voltage coil with insulation paper layers between the coil layers.
2. A coarser coil below that, in the blue coil form, is I believe a charge coil that produces the power to be trapped by a diode into the large charge capacitor (400v dc?).
3. Then at the mid point of flywheel (magnet) passing the coil... the zero crossing of the voltage pulse (single sine wave the transistor is triggered to dump the power from the cap through the coil primary....SPARK generated.
4. Simple CDI ignition

Bad (thermally sensitive until it finally dies) transistor or charge diode and the process goes down the toilet.

[sweepleader]

I have wondered ever since I first saw these how they triggered the spark, very simple indeed. The zero crossing sine wave never occurred to me. Very nice, now we know.

How did you open up the potting?

[dynodave]

I use a hot air gun to soften the brown potting and then you use a "dull" digger and have at it... heat dig heat dig heat dig. The black case is just a fixture to hold the components while the potting is being poured and curing. It comes off quite easily under heat.
I will next remove the components and test the transistor(SCR?), diodes and capacitors. There may be 3 sections of coil but I will only find out upon final destruction of the HV coil and charge coil. It would be inside probably the HV coil maybe 50-100 turns of bigger wire.
The two terminals are a ground for HV return from the plug and the second to short out(off switch) the charge pulse to keep the saw from running.

[sweepleader]

When you mentioned "zero crossing" I thought SCR. If I am not mistaken, I am pretty sure they use zero crossing control for lamp dimmer and motor speed control, seems like that would work here too. It has been many years since I had anything to do with that. I earned my living as an auto mechanic during the change over from points to electronic ignition so I learned a lot then. I would suspect there are only 2 windings on the coil and that your estimate of 400 volts on the primary would be in the ballpark for the instant of "opening"/spark. I have been bitten more than once by the primary side of the circuit during tune ups. Oh yeah, and the secondary side too.

I had a friend who rewound motors. He sawed through the coils, then counted the cut ends of the windings to get the numbers he needed to rewind. Of course he could not unwind the coils inside a motor if they were intact.

Dan