Shindaiwa T20 neg or pos ground ignition set-up?

[johnl_]

I have a Shindaiwa T20 string trimmer with no spark, coil has continuity, and not shorted, looks like the ignition module may be bad. It is separate from the coil, original module part# 20035-71710 (NLA) or 20035-71700 (new). I bought a Stens universal module to try, #440-465 because much cheaper. The instructions have you choose a positive or negative ground set-up, I don't know which it is. Will I burn out the module if the wrong polarity is used?

[KE4AVB]

Should cause a problem other than the ignition timing will be considerable amount and the unit will not start. And the odds it going to be negative ground is fairly good too.

[bgsengine]

NOt so much being pos or neg grounded, as it is determining the trigger point (leading or trailing trigger) given the sine wave of the AC Voltage generated in coil. one way it'll fire, the other it won't (or it fires out of time) Plus , from experience with many of these 2-piece systems, often the universal module won't work with them any way.. This might be one of those rare ones where it will work though, but sorta kinda doubt it

[KE4AVB]

An AC sinewave is both positive going and negative signal though most forget there is a zero voltage crossover point. Here what they are referring is rather if when the flywheel magnets generates a pulse if it is first positive or negative. This is due to arrangement of the North/South poles of the magnets. The older Briggs cast iron engines for an example had flywheel magnet polarity reversed of today's Briggs engines which an initial negative pulse which made them positive ground.

Following is the sine wave generated. Left is with the magnetic poles one way and the right is after the magnetic poles have been reversed.

As you see the trigger point shifts if the ignition module is set to the wrong polarity as the initial pulse can be either positive or negative depending the polarity. Only a few universal trigger module were designed to switched between the two modes.

[Arkie]

I have a Shindaiwa T20 string trimmer with no spark, coil has continuity, and not shorted, looks like the ignition module may be bad. It is separate from the coil, original module part# 20035-71710 (NLA) or 20035-71700 (new). I bought a Stens universal module to try, #440-465 because much cheaper. The instructions have you choose a positive or negative ground set-up, I don't know which it is. Will I burn out the module if the wrong polarity is used?

I've tried chainsaw engine electronic ignition modules that polalrity could be selected as neg or pos.
Usually (if no instructions included with the module
Leave the spark plug out (to reduce compression for a good crank spin) and look at spark for neg ground first.
If spark install and see if you get a run. If not reverse polarity to positive ground and test.
Some of them universal modules won't run at all even though you get spark and some will run with the engine slightly out of time and seems timing is usually too fast. (engine cranks over hard)

I've never had any good luck using the non OEM electronic ign modules on chainsaw engines. If I got a good run the module would not live very long. (and some modules with same part numbers would act diffeernt on same engine)

Summary:

You are just rolling the dice and hoping for the best.