I have a SNAP ON tools / 115 vac Growler (armature tester) it is the MT320A model and has the light bulb, on-off toggle switch, two leads and the V-shaped laminate base for the motor to sit in while testing it. I need an electrical schematic for it so I can repair the fraid wiring. It has two coils, and each coil has 4 wires (yellow, red, black and green) If anyone out there could help me it would be greatly and I do mean greatly appreciated very much. Thanks. Don
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Measuring across the commutator opposites is a rough check - if each pair has the same resistance it is probably good but even then there are no guarantees. I have never seen the armature resistance stated for any motor though that doesn't mean such figures don't exist.
It would seem logical that each pair should be isolated but that generally is not how the armature is wired and each commutator segment is the termination of two coils.
In reality there is only three ways to test an armature - either build it into a motor and see if it performs ok, use an automated motor fault analysis machine or one of the dedicated armature testers such as an armature growler.
Hi get the motor field coils & armature checked for shorts u can check the field coil with a multimeter / it would b advisable to get the armature checked on a ( GROWLER )....cheers
It sounds like the armature is bad. It should have an even dark ring around the bars of the armature commutator where the brushes ride. If one or two of the bars is discolored above and/or below that it could easily be bad. It could also be pitted between a couple of bars. Normally the space between the bars is even all the way around and nice and "clean cut" looking. If you have access to an armature growler you can test the armature. Hope that helps.
There could be an issue with the oil sending unit, spark plug boot or faulty on/off switch. Easy tests. Always use a new plug for testing. Unplug the oil sending unit wire and retest for spark. If spark may need to change the oil or low oil. If still no spark, leave the sending unit wire unplugged and remove the boot from the plug wire. Insert a short piece of paper clip wire into the end of the plug wire and hold near metal of the engine for test. If spark, replace boot. If still no spark, unplug wire from on/off switch and retest. If still no spark suspect faulty coil ~ redo all tests using old coil. If still no joy return new coil for exchange. I use a growler to test coils(growler used for testing armature for short, place one leg of coil on each pad of growler and activate growler for short burst). Good luck.
Always have a new spark plug handy to determine if faulty plug when no or weak spark. If your engine has an oil alert, disconnect sensor wire and re-test. If still no spark suspect spark plug boot or coil. New or used coils are available at small engine repair shop. If you have access to growler (used for testing armature), by placing coil on growler with one leg on each pad, you can test coil for signs of life. Good luck
Sounds like your brushes are used up. Take the brush caps off on each side of the grinder handle, if the carbon is 1/8" long or shorter they have to be replaced. (Makita Part #191938-1) If you overworked the tool (put too much pressure on while grinding) it's possible the armature and/or field overheated and burned out. They are Makita Part #517301-4 and #521621-0 respectively. You need a growler to check these items to see if they're shorted out.
Save yourself a lot of time and headache. Take the motor to a motor repair shop (also try starter and alternator shops as well) and let them pull the bearings off. They already have the tools, pullers, specialty vices and such to make the task easier without damaging the laminations or bending the shaft. They can also put the armature into a growler and tell you if the motor is even worth working on. Shorted windings are not uncommon on older units. Start there, it will be worth the few dollars and minutes it takes.
They might also have a replacement motor that is just a few dollars more than bearing service, particularly if yours tests good electrically. The motors in RVs and such are not unique, actually pretty common, and therefore cheap.
More than likely you have a worn brush. If the breaker was running good and then just stopped this is the case. These brushes have a pop-off feature that will stop the motor when it is time to replace the brushes. If you replace the brushes and are getting a lot of sparking, the armature or field more than likely may have a short. Sometimes its the armature, sometimes it's the field, and sometimes its both (running short). You have to have a short tester and a growler in order to test for the shorts. One thing to look for is any burn marks on the windings of the armature, and look for scarring on the inside of the field which may have gotten damage due to rubbing from the armature. An imbalance in the electrical field can push the armature into the side of the field while it spins.
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