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John Deere Tractors Discussion Forum
Show Parts for Model:

Wico X magneto coil; test procedure?

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Todd Wiscal

04-29-2006 22:23:08
71.193.2.58



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Is there a specification or procedure for testing a Wico magneto coil with a good multimeter?




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Glen in TX

04-30-2006 18:56:56
208.246.9.71



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 Re: Wico X magneto coil; test procedure? in reply to Todd Wiscal, 04-29-2006 22:23:08  
Specs. for Wico coils from Graham Lee tester manual.
Coils:
X2766, Wico C & A, 8500 ohms max. secondary resistance, 1.0 max. primary.

X5700, Wico XH & XV, 7000 max. secondary, 1.2 max. primary

X5700B, Wico XH & XV, 9000 & 1.2
X5700C, " " ", 8500 & 1.5

X6936, Wico XHD & XVD, 6500 & 1.2

(Secondary is read from points wire to coil button output) (Primary is read from points wire to ground wire) I didn't include test readings for the XB or AP or APH Wico.

Like John T said these are only tests for secondary and primary open or closed circuits. A true coil tester will put a load on the coil heating it and give it a high voltage output loaded firing test which will indicate insulation or circuit breakdowns inside the coil. We also do a outside high voltage leakage tests on the coils as well. Those readings are specific to each coil and series and the coil testers test charts. So just because it passes a ohm reading test doesn't mean it is good. On condensers we do more than just test with a ohm meter and test for microfarad capacity, series resistance, and leakage breakdown tests.

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John T

04-30-2006 06:27:55
66.244.90.5



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 Re: Wico X magneto coil; test procedure? in reply to Todd Wiscal, 04-29-2006 22:23:08  
Todd I can describe a procedure to use only an ohm meter to tell you if a coil is indeed BAD but it will not tell you if its necessarily GOOD. You need a regular high voltage coil tester for that cuz many common failures are due to high voltage breakdown and especially once up to temperature, which the low voltage ohm meter simple continuity checks will not reveal. This assumes its a Wico C or X mag NOT a Wico XB distributor.......

NOTE: It still takes a decent quality ohmmeter to measure these low ohm values which should adjust/null out to zero with the leads shorted if an old fashioned analog type.

A coil MUST pass at least simple continuity tests in BOTH the low voltage primary and high voltage secondary windings and NOT be an open, cuz if EITHER winding is open its BADDDDDDDDDDDD.

PRIMARY If you remove the wire from the points leading to the condensor and any kill switch stud wires (if it has one) youre left with the coils low voltage primary wire on the points so if when the points are open or that wire is simply removed (best way to test) and you place an ohmmeter on it and case/frame ground (provided the ground lead is good and connected) you ought to measure maybe in the 0.4 to 1.0 or so ohms range. If its an OPEN circuit its bad or the ground lead isnt well grounded, they can get broke off or the screw grounding them be bad or loose!!!!!.

SECONDARY If you place the ohmmeter on the coils side high voltage output terminal/button and case/frame ground, it ought to read 3000 to 7000 ohms or so and NOT be OPEN or else its bad or the ground lead is not grounded (see above).

Also smell the coil for the burned electrical insulation smell test and/or see that theres no ugly oily sticky black gooooooooo has leaked out.

If the coil passes BOTH tests and the condensor is NOT bad or SHORTED (condensors go bad you know) and the ground pigtail is grounded and its not a smeller or leaker theres a good chance its good so look for other problems like bad bushings causing the rotor magnet to drag and other problems.

Another easy test is to replace all the wires on the points and put an ohmmeter there and to ground and manually open n close the points and the meter ought to read zero when points are closed (unless they are burned or putted or carboned or not closing) and the 0.4 to 1.0 when open. If she always a dead short even when open and the coils primary is not shorted, suspect a bad shorted condensor (try with its wire removed) or a kill switch wire (if it has one) or the kill switch stud is bad n shorted (if it has one and its wire is connected) try removing its wire n see what happens.

DISCLAIMER these ohms values are not exact but should suffice for the purposes and limitations of the test I described, Duane or Glen could give you more exact and correct ohms values but that still depends on the particular model you have and the coil, REGARDLESS if its OPEN its baddddddddddddd.

Ol John T in Indiana (NOT a mag repairman but have worked on mags and been to a goat show and calf roping in my day)

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J Schwiebert

04-30-2006 09:57:36
209.143.51.159



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 Re: Wico X magneto coil; test procedure? in reply to John T, 04-30-2006 06:27:55  
Hey John T. I would like to contact you. Thanks.



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John T

04-30-2006 10:24:36
66.244.90.5



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 Re: Wico X magneto coil; test procedure? in reply to J Schwiebert, 04-30-2006 09:57:36  
my e mail is jmn50@msn.com



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