Workzone "dremmel" low revs and faultering

100nF, 250V, X2 class block cap, across the 2 wires to armature and stator, good ESR but only about 50nF. Perhaps spark eroded away and now arcing across internally, anyway will find a replacement for that and retry on mains

My Dremel sometimes fails to start, but runs ok once push-started. Bad at low speed. Commutator looks ok, so I was assuming internal shorts in the armature, rather than problems with the controller. Am I wrong?

A similar problem to yours however...

Ordinarily, stuttering means the brushes are sticky or dirty, and not making consistent commutator contact. It could be, though, that your triac is false-triggering (there ought to be a gate-to-cathode resistor or resistor+capacitor that prevents false triggering).

Are you sure that component is a triac? There are similar devices called 'quadracs' that have an inbuilt trigger.

If there are shorted turns in the armature, the motor will run slow, vibrate and get very hot. The shorted turn is acting like a brake. An open in one wire will make it lose torque, and possibly have a dead spot where it won't start, but otherwise will mostly run.

Jon

Main control is a Z0409MF triac. If a short in the windings then it would not work well on DC, even if only 60V. I'll try a diode on a variac while the pcb is removed to check for higher V internal arcing. In a couple of hours I'll put in a new 100nF and crack open the old one and look for errosion of the film metalisation. Generally I'm very impressed with this Workzone WCT 135, I bought a second for a spare luckily. Just 2 safety issues, needs a shroud around the on/off switch and a brake on the pot knob from vibrating around, both easily modified.

no overheating or smoke/smells. Cold testing showed consistent 12.5R segment to segment, consistent

50R across brushes and 120R overall, while turning the rotor

With a 1n4006 on a variac, perfectly happy with 70% mains , quasi DC , presumably about 180V peaks. Autopsy on the cap. No obvious smoke trails inside or burning smell, just a "chemical" hot polyester clothing out of a tumble drier sort of smell. Minimum metalisation mid way into the bulk of the layup, only 1/3 of width of metal remaining, so presumably local heating there so run away and the metal there looked very suspect , grey, not mirror and microscopic pin holes

Back to perfect working order. Quite a bit of space in there but no

100nF 400V(decided to up from 250V rating) cap laying around, but 4x .47uF 100V in series went in there with room to spare. This will be a stock fault with these nice compact drills, I use mine on a daily basis it seems. While in there a better idea of anti-vibration fudge for the pot knob, simply a small O ring over the pot shaft, before replacing the knob, to bind slightly as it is compressed slightly when fitted in the casing. I left the TIC226 triac in there as running perfectly normally.