Sparking/squeaking Testarossa motor

[cigmas]

No, not that Testarossa. But for some women, this is the more important one. Hair dryer Testarossa by Conair, model TST335C.

Sometimes the motor is making a horrible screeching sound (enable audio in the video clip) and sparking from, I presume, the brushes and commutator. Other times it functions fine. Both situations are captured in the short video:

https://i.imgur.com/IXR5Uy3.mp4

What's wrong, and is a repair feasible?

[KE5FX]

Ah, yes, the Testarossa, equipped with a SLOW DOWN light for each cylinder bank that comes on to indicate that the catalytic converter for that bank is currently on fire.     At Pebble Beach, they would look for the correct SLOW DOWN 1-6 and SLOW DOWN 7-12 lamps, rather than a quick and dirty part swap with a lowly 308QV.

Wonder if shorted turn(s) in the field winding would do that.  It seems to run smoothly at some starting angles, not so much at others.  Amusing failure mode, but probably beyond economical repair.

[james_s]

How are the bearings? Failing bearings can make all kinds of nasty noises. I'd also check the brushes and try cleaning the slots between the commutator segments. I was given a nice cordless drill that would spark and smoke from the brushes, I replaced the brushes and it didn't make much difference. I used a razor blade to scrape out the slots between the segments and it works like new.

[cigmas]

Ah, yes, the Testarossa, equipped with a SLOW DOWN light for each cylinder bank that comes on to indicate that the catalytic converter for that bank is currently on fire.    

This Testarossa could use a light like that too

How are the bearings?

The shaft is held solidly without play and the rotational resistance is consistent. Turning the shaft is neither "free spinning", nor rough/stuck. It's even with a bit of friction.

As for sound, when manually rotating slowly there is a certain twanging like that of a compressed spring. I've attached a short mp3 recording. The finger sounds and plastic creaks are louder, but listening carefully, the periodic twanging/creaking is noticeable. Does that say anything?

I'd also check the brushes and try cleaning the slots between the commutator segments.

Good idea. My first inclination was to clean out the hairs that got inside despite two meshes at the air intake. The shaft under the fan blades has a moderate bunch wrapped around it. The commutator is also blacked with a fine powder (carbon from the brushes?) everywhere. Can I use isopropyl alcohol on it?

I'm also not sure how to remove the fan even after removing a nut from the threaded copper sleeve over the shaft. I'm not sure if the fan blades are attached or screwed to the brass sleeve or if it's all one piece. The threading seems to stop before reaching the metal part of the fan, so I would think the fan should just pull off.

[Gyro]

That's a tapered collet, just like the ones used on rotary switch knobs. The threaded piece has an outward taper with slots in it inside the fan hub which grips the shaft. the fan hub has a matching taper to close the slots. the fan should just pull off with little persuasion. Maybe a quick tap on the end of the shaft.

Note the length of exposed shaft so you can put the fan back on at the right distance.

[cigmas]

That's a tapered collet

Ah, that makes sense. Though I would expect a collet to let go more easily; it's really stuck on there tight. I've tried a bit of penetrating oil, hammer taps on the shaft, lots of tugging... it doesn't budge even a little.

And thanks for the tip -- I've noted the length of the exposed shaft at 3-4mm.

[cigmas]

Seems to be solved! Looks like it just needed some cleaning.

I cleaned the commutator by manually rotating the motor and pressing a paper towel with isopropyl alchohol, being careful not to leave lint pieces behind. I also used a toothpick to clean between the segments a bit -- it couldn't really reach all the way into the crevice. It's still blackened, not shiny copper like in many commutator cleaning videos out there, but this first try worked well enough. With multiple on/off tests, I could not get the squeaking/sparking anymore.

As for removing the fan hub, I still didn't manage that. It'll have to wait till next time..

Those of the long-haired persuasion are happy enough now.