Thread: Stihl Electronic Brake

Hi Ratbag,

your guess about the electric brake using polarity reversing is spot-on. It is one of the functions of the electronics module, which is housed inside the hind grip handle. I'm afraid that you will have to replace that if you want to have the brake function back.

The MSE 220C (nowadays MSE 220 C-Q, with "C" for controlled starting and braking and the "Q" for a separate mentioning of the brake system being very quick) started off as the E20. This first model had a 2000 Watts motor with a current limiting startup circuit. This model only had the mechanical emergency chain stop, operated by either moving the black hand protector bar or by sudden upward movement of the bar (by means of an inertia mass inside the housing, that trips the actuator spring. The actual emergency brake consists of a steel band that spans tight around a hollow steel clutch drum on the motor armature. This drum is adjacent to the motor's centrifugal fan array. When the triggered sprung mechanism spans the band around the drum to stop it spinning, the mechanism also operates a switch that cuts off the motor's power. This mechanical brake system has been part of this model from the E20 up to the present MSE 220 C-Q.
When the E20 was still around, the assortment of Stihl machines was more modest than today. Everybody knew that 08, 026, 066 070 and 090 related to chain saws, Stihl's core business products. The few other machines like the grinders bore names carrying abbreviations of their purpose (TS stood for "Trennschleifer" or cutting grinder). But when the range of products grew, it became necessary to give the saws their own abbreviation of "MS" ("Motorsäge" or motor saw). So the next version of the E20 would have been an MSE20, but the motor was cranked up to 2200 Watts, so it became MSE 220. I'm not absolutely sure about this, but i believe the E20 featured a resistor type current limiting starup device. This resistor was combined with a special switch, containing in fact two switches, one of which with a time lag of 1 to 2 seconds. When squeezing the trigger, the first contact closed and fed the motor through the resistor, avoiding it to absorb full mains startup Amps. After the time lag the second contact closed, bridging the resistor and connecting the motor directly to the mains. This current limiter style has been used in heavy industrial angle grinders (like the Flex L2106VC) until quite recently, because the loyal but conservative heavy users of such grinders still regarded electonics as vulnerable and less reliable. The failing of the module in your saw (two times no less) proves that they have a point.

The MSE 220 had no resistor, but a triac type module instead. The triac circuit was set at approx. 70% maximum output, which gave the same startup result at limited current. The double-action time-lag type trigger switch remained the same. The E20 and the MSE 220 featured a mechanical type (bi-metal operated) overload current protection device (recognisable by a littel green button in the machine's housing).

A further development of triac device were the MOSFET (metal oxide doted silicon chip based field effect transistor) and the IGBT (isolated gate bi-polar transistor), both very fast switching transistor types, with low internal resistance and high amp capacity. IGBT's are used in modern battery drill drivers, in the modern Festool plunge saws, and in a vast range of other tools. IGBT control devices are combined with purpose designed integrated circuits, which can be fitted with additional input terminals for sensors, like heat sensors (overheating of motor windings), tacho generator coils (for constant rpm regardless of load) and overcurrent. The first MSE 220 C model only featured curent limited startup and polarity reversed pulse braking. A mechanical Klixon device detected heat in the field windings.The module in the later C-Q model can sense temperature rise and overcurrent, so all control functions are incorporated in the module itself, but i believe that the C-Q lacks constant rpm control. To provide the electric braking function, the module in the C and C-Q needs separate connection for the field coils and the armature. When the trigger switch is let loose, the module reverses the polarity of either armature or field and feeds a pulse to the motor of about 20% full mains power. The reverse torque quickly slows down the moving parts and the short reverse pulse is visible as rather nasty sparking of the brushes. Stihl (as do Festool and others) remind of the fact that brushes wear quicker in machines with electric braking.

I have never closely studied the wiring diagram of an MSE 220 C. Example: i do not know for sure what causes the pulse after the trigger switch has cut off the mains power. The old triac circuit was series-connected with the motor, and bridged by the second time-lagged switch inside the trigger. And one thing's for sure: when that trigger was released, there was no mains power allowed to any part of the machine anymore. Yet the brake electronics are allowed to emit a pulse, so they must still be connected to the mains power somehow, parallel to the trigger switch. So i couldn't tell for 100% sure what component has failed. There is a set of IGBT's inside such a device to allow for the polarity reversing. One is enough for startup current limiting.

Does your saw still start up in two steps, as before, or with the sudden jolt of direct connection to the mains?

When replacing the module, there's another thing. The MSE 220 is an easy saw to take apart but finnicky to put back together again. That's mainly due to the oil pump's gear wheel, which is sandwiched between the drive train and the sprocket shield. This saw must be built together again in layers, as it were, in a specific sequence. I have a regular MSE 220 without electric brake. It performes well, but i was rather disappointed when i took it apart. These plasticcy machines are in a better league than the flimsy gardener's style MSE 140/160/180/200 B-Q range, but then the price tag of the 220 has been stiffened proportionally. All of these saws are not worth their money in my view, but that goes for most electric gardening tools. What a difference the old E15 and E30 were! I love those.

greetings and success!

gerhard

Gerhard, you're a gem!

I'd noticed previously on this forum that you'd been within the bowels of an E220C (and weren't particularly complimentary regarding the construction of the gear-train), but couldn't relocate your particular post.

I was rather hoping that you'd pick up on my request, given your astonishing expertise regarding Euro power tools, but felt it impolite to address my request to you directly.

I suspected that the electronics module would require replacement. However, when my first saw was "repaired", it was this item that was replaced, to no avail! One thing that I've noticed with the saws is an intermittent "freezing" of the saw on startup, as if the electronic brake is still applied: the motor hums and strains, but cannot overcome the brake to begin rotation. This occured immediately prior to the brake failure. Although it's happened on numerous occasions I've only ever allowed this "seizure" to occur for a second or two; just sufficient time to recognise a problem, and release the trigger.

I don't think that you should dismiss electric saws as being mere toys. It's a common misconception amongst saw users, perhaps based around their relative lack of power and the inconvenience of the power cord. Good quality cord should provide barely measureable voltage drop over distances of 60m, more than enough for all but the most expansive of yards: up to 11,000 square meters!

Most commercially available "budget" saws are indeed toys. However, the Norwegian-built Husqvarna that I use at my shack is ideal for pruning maintenance, firewood and tree surgery chores.

The Stihl E220C is in a class of it's own. It has similar power characteristics to my 026 petrol saw, the smallest of Stihl's range of "Professional Forest Harvesting" saws. It has been a hire industry favourite for years by virtue of it's power and robustness. I have 5 saws available: 090, 064 and 026 Stihls the Husky and the E220C. They all have different uses, strengths and weaknesses, but the saw I prefer to use within reach of a power source is the electric Stihl.

Using saws in hardwood, power isn't necessarily the best alternative to torque. An electric saw offers torque in spades, even when loaded up within the cut. I can remember using a Stihl E30 as a young trainee Ranger in the 70's on a mill skid docking logs to length for a sawmill. It was, and still is, the biggest, heaviest, most powerful and scariest saw I've ever used, even compared to my 090. The three phase motor was enormous, extremely heavy, and thanks to the heavy rotating mass, took forever to run down. Despite the front heavy nature of a four foot bar, the thing had a kick like a mule, and was, if the tip was pinched in the cut, all too ready to kick backward and upward around the rotating axis of that enormous motor. It was a week of sheer terror! There's no love in me, despite it being Valentines Day, for the E30!

It's just downright antisocial (and illegal in Tasmania) to use petrol saws in built-up areas these days when there's quieter alternatives available. Which is better to maintain neighbourly relations: a screaming, fuming 2-cycle petrol motor or a constant-running quiet electric? Quiet enough not to require ear muffs!

My household runs on firewood: cooking, heating & hot water. I prefer to harvest dead, standing trees that have been suppressed and killed by their brethren in regrowth forests. Older dead trees have nesting hollows, an important habitat for native birds, reptiles and mammals, and are a disappearing resource in our native forests. These "poles" can be easily harvested by hand in 2m lengths, transported on my ute and processed at home quickly & efficiently in bundles. Door to door in less than 2 hours for 1.5 tonnes of bone dry, fire-ready firewood, and no splitting! Petrol saw in the bush, electric @ home.

Over the last 2 days, I've been visited twice @ my jobsite by irate Shire officials over my smoky fire-pot, being threatened with fines. I'm therefore unwilling to tempt providence by using either petrol saw again, despite extensive remedial work being required for the badly overgrown fruit trees.

In reply to your questions, Gerhard, do you think that a storage capacitor could be providing a discharge current for engine reverse braking? This would explain the momentary nature of the high current discharge and sparking with no voltage available from the supply side. My saw, as always, starts with more of a progressive runup to max. revs than a two-stage startup. I liken it to a 9" electronic soft-start Metabo grinder, for example, of about one second duration. The only issue is with the rundown. I timed it today at about 5 to 6 seconds, which is a bit unnerving for ladder work!

As always, thank you very much again for the extremely comprehensive nature of your reply. I feel a lot more confident to tackle the problem now.

Hi Ratbag,

i did a study on the Stihl type of electric brake over the weekend and i wish i had done so earlier. It is now clear that i was wrong in claiming that the braking action was achieved by reversng the armature's polarity. Instead Stihl reverses one of the field coils. So i was wrong on that account and i apologise for having misinformed people and for possibly having invoked mishap because of that. I will sure take better care next time!

I didn't see such array in a power tool as yet, but when searching further on the web, i found that some Makita SMCS-saws use it as well. Some twenty years ago i did find such a brake array in my Braun MP50 juicer, though, which has an induction motor. This model doesn't automatically eject its pulp, so its needs intermittents stops to clean it out. Because the motor is near frictionless, spinning down takes more than a minute and for that its switch has an additional pulse setting for a quick stop. Reversing one of the two field coils puts the rotor in a one-magnet-pole-only setting, which induces Eddy-currents in the rotor bars and these provide the stopping power. The same braking effect is achieved by feeding DC to an induction motor.

I found this out as soon as i saw pictures of the actual field packs of the Stihl saws. They had fixed leads for the brush holders, as any conventional brush motor field pack has, so reversing of the armature was out of the question. The Stihl and Makita field packs, meant for models featuring electric braking, did show an extra wire that stuck out from one of the field coils, so this must be the wire that may provided the field coil reversing. So, in the end it is safe to say that the secret must be sought in the combination of the field and the switch and/or electronic circuit.

Your capacitor suggestion is interesting, but apart from that you would still need the reversing switch array. An MSE220C has a nominal input of 2200 Watts, meaning an idle input of approx. 700 Watts (idle Wattage intake is often around 30% of the nominal load consumption). 300 Watts are spent generating the cooling air flow, driving the mass of gears, armature, chain and oil pump and the rest of the power is spent on overcoming friction and generating heat and noise/vibration. So a short reverse jolt of 100-300 Watts (over a period of 1/4 to 1/2 second) would contribute nicely to a quick stop. The charge capacity of one Farad is capable to emit 1 Amp current over a period of 1 second (as an average; the start voltage would be high and the Amp count very high, subsiding into a quickly dying voltage and simultaneous drop in current). 200 Watts would mean approx 1 Amp and such a jolt during 1/4 second would mean the charge capacity of 0.25 F = 250 times 1000 microFarad. In practice you would need a bank of 50 to 80 capacitors of 1000 uF to build up the jolt. Electrolytic DC capacitors are cheaper and more compact to AC equivalents. But that would be okay because you can brake a brush motor with reversed coils by means of DC even slightly more effectively as with AC. So it could work, but it would be like sticking a battery pack to a mains powered tool. You could also use a multi-contacted relay and a push button to provide a hand-operated electic brake, in case you need one (which isn't all the time).

As illustrations, i added schematics of the 220 and 220C for comparison. The moduel sure does make a lot of difference and it is a tough challenge to rpelace it with something just as effective, since it controls a lot of functions.

You mentioned your saw humming while starting. The electric brake may indeed be activated, but that could also be the fault of the switch instead of the module (which behaves good otherwise, i read in your reply). I'll be back with more soon, since right now i'm pressed for time. Till soon!

gerhard

Found it! Stihl patented -of course- its electric brake system, for instance in America. Over there Stihl's application received the entry as United States Patent no. 4680862, and i found this abstract, describing the patent's main feature and principle:

Abstract:
A motor-driven chain saw is electrically operated by means of a universal motor and has two brake systems operating independently of one another. A mechanical brake system serves as a safety brake and when actuated, the mechanical brake system brings the saw chain to a standstill instantaneously. The second brake system is an electric coasting brake, which when the switch is released stops the saw chain quickly but without recoil. The electrical braking is effected by reversing the polarity of one pole coil of the field winding and short-circuiting it with the rotor winding.

So now we're sure that there is no reversing of the armature polarity involved and that a field pack with an additional connection is used. Two questions remain:
- what does this look like in a schematic drawing?
- can such a brief reverse connection upon switch-off be achieved by the switch alone (without the electronic module being involved) or is the cleverness an integrated part of the module, making it indispensable?

To be continued... back soon with more!
gerhard

Hi,

another step. Found the wiring diagram of the Makita LS1214 saw. Same principle, by the look of it. But still not sure about the wiring of the field coils, and about the way in which either the switch or the electronics are involved. See attachments. If anyone has an idea how the reverse switch cyvle works before i found it out, feel free to comment.

Hi Ratbag,

About another topic in your interesting post. True, i was disappointed about the E220’s construction. For a price tag of almost 600 Euros i expected more than merely a bigger size of an otherwise standard consumer chainsaw construction. By chance I had some boxed restored Stihl electrics that i hadn’t brought to my rented storage space yet. So they were easy to get at and set up for comparison pics. The E220 is the most boring model of them all and looks just as bland from the outside as it is from the inside. Yes, the E30 and E15 are from another era, but that era hasn’t died yet. The E30 is still in production today, by the Austrian firm Prinz, as model EED. The inline design of the E15 also has some successors that aren’t half bad. Take a look at the Prinz E21 and PowerCut 2700. Or at the Vimal-64 from India. Heavy metal stuff, with robust steel gears. Compared to those, an E220 looks like a household appliance. Sure, the popular Makita/Dolmar and Husqvarna/Jonsered inline models and most sidewinder style models all have plastic gears, like the E220, but you can buy two or three of those for the price of one MSE220C-Q.
Back soon with more. If anyone wants details on the E30 and E15, let me know and you're in for another yarn (six miles instead of six lines) .

pics of the Prinz and Vimal saws

That's fascinating stuff, Gerhard.
Perusing your photographs has confirmed just what a monster saw the E30 is.
As it's three phase, I suppose that its main purpose in life was as I had used it all those years (34 or 35) ago: docking large logs to length in situations where a 415v. supply was conveniently available, such as sawmill skids and loading bays. In my case, it wasn't just the weight of the saw to be considered,but the 50 odd meters of heavy duty armoured 3 phase cable that needed to be dragged around with it! Quite a handful for a mere boy!

I'm fascinated by the E15 saw. I've always found that "in line" motors on these saws are much more convenient to use. My first electric saw was a Chinese clone of the Husky/ Jonsered style. It was a fantastically powerful saw (rated at only 2000w), but naturally only short -lived. My saw had a suppression capacitor failure I think, causing alarming armature sparking. Had I been diagnose the problem at the time I could have effected repairs, but instead it was consigned to the bin, as most inexpensive asian tools are these days, as an unrepairable "disposable" tool. Modern versions usually have "soft start" electronics, removing the unsafe sideways 45 degree initial kick of inertia on startup.

My replacement saw was a Norwegian made Husky. Quite a good saw, but much lower geared, I assume for additional torque, which actually made the saw much slower cutting than the Chinese copy! At least it's still going.

Back to the E15. By the look of the photographs, it's single phase, and I'm guessing that it has a universal motor. Are those brush hatches at the rear of the motor casing? I can't see much in the way of air vents at either end of the saw, and that together with the diecast housing and angle grinder style bevel gears would make the saw become quite hot in extended operation I'm guessing!

These saws would be extremely useful for carpenters and builders in that the relatively low profile would make them a safe, quiet alternative to circular saws in tight, inaccessible situations. Despite claims to the contrary, I've always regarded a modern inline chainsaw as a safer tool to use & operate than a circular saw of equivalent capacity. Sidewinders are much less convenient to use for framing work, just as in circular saws.

By contrast, the Vimal saw you've illustrated looks anything but safe! There's no concessions to operator guarding at all, on either the trigger or handle ends. Presumably there's no braking mechanism either. In fact it's quite a scary saw all round! I presume chain oiling is also manual, necessitation removing one's thumb from the safer wraparound position to pump chain oil manually during operation!

Hi Ratbag,

Yes, the Vimal 64 is a very old design and its use is forbidden in many parts of the world. It has a hand oiler and i’m not sure if it has a brake. But i just added this example to point out that durable metal electric chainsaws are not extinct yet. Vimal also makes some very nice three phase saws. One model harks back to one of the first Stihl two-man saws and its safety specs are also not up to date, but some other models are very modern and feature brakes and automatic oilers.

The E15 design is from the late 60’s and –although the 3 kW power of an E30 could not be drawn from single phase 220 Volts without fusebox and wiring ploblems- it was still meant as Stihl’s heaviest single phase alternative. A single phase induction motor was ruled out because of its lack of torque. Asynchronous single phase motors have good efficiency and torque if the difference between field rotation speed and rotor rotation doesn’t grow too big. Two pole async motor usually run at 2850 rpm on 50Hz and torque and output remain good if the load speed doesn’t drop below approx. 2600 rpm. Below that, the torque collapses quickly and the current intake increases dramatically, with much of the power converted into heat. So, where three phase motors with their much stronger rotational field will overcome heavy load peaks, single phase motors will stall. Brush motor series wound motors, on the other hand, have excellent torque in adverse circumstances and are a much better choice for a single phase chain saw.

The rule for professional grade chain saws is: one hp for the first 25 cms of bar length and one hp extra for every additional 10 cms. So a 35 cm saws should preferable have a 2 hp motor, meaning approx. 1400 Watts output for an electric. Really durable two horse brush motors were expensive to develop and build in the 60’s and the market for this machine type was probably not big or lasting enough for Stihl to venture such an investment. So they searched for a readymade motor instead and the strongest durable brush motors light enough for handheld use were to be found in the power tool world. 1400 Watts output would mean (with the efficiency figures of that era) an input value or 2400-2800 Watts, and the startup current peak of motors with such ratings had a fair chance of blowing 16 Amp fuses. So Stihl had to downgrade its design demands a bit, partly because wattages beyond 2000 were “very big” in those days and 2000-plus motors hardly existed. One of the biggest brush type tool motors in the 60’s was the 2000 Watts Elu MOF11 router motor, which alone already weighed 7 kilograms and was built far too generous (big axle and large bearings for routing precision) for a chain saw. Furthermore, its 18000 rpm would be too much for direct drive and the lack of a suitable of-the-shelf gearbox soon made this motor an unrealistic option. Circular saw motors did have nice speed reduction gears and their arbour’s output rpm also fit the bill perfectly, but the largest circular saws of the day featured only 1350-1600 Watt motors.

The best options were therefore found in the only remaining heavy tool type: large industrial angle grinders. Series production of such machines is large-scale, so purchase prices would be lower than prices asked for smaller scale custom designed constructions. The gearbox construction was also ideal, since most angle grinders allow for rotating the box and the disc arbor 90 degrees. Ackermann + Schmitt (Flex) and Bosch types probably had too many protrusions and the firm name was cast onto the housing. The housing of the AEG machines was relatively smooth and generic and the 1900 Watt versions were at that time one of the most powerful machines on the grinder market, with a output somewhere between 1200 and 1300 Watts. AEG made two versions, the 6600 rpm (230 mm disc) WSA1900 and the 8500 rpm (180 mm disc) WSB1900. Stihl chose the 6600 rpm version. The WSA1900 was also available with a built-in relay and a startup resistor, to limit the current surge during spinup. This machine could even be used on 10 Amp fuse, whereas 1900 Watts without current limited startup was just about the limit to leave 16 Amp fuses intact. So these ratings fitted Stihl’s bill. An additional advantage was the WSA1900’s cooling airflow, part of which was guided through channels integrated in the gearcase moulding. Other reasons for Stihl having chosen AEG are probably AEG’s willingness to make the machine in a mirror image (for regular angle grinders would only drive chain saw assemblies in the proper direction if the bar was mounted on the left side of the machine) and doing so for an attractive price. Also, AEG is the most renowned German name as a deliverer of electric motors for every possible drive (up to U-boats). So is Siemens, but Siemens was never involved in tools as big as AEG was and thus was not nearly as experienced in that field.

The agreement between AEG and Stihl was more of a bi-lateral exchange, by the way. AEG bought back saw frame parts from Stihl and was allowed to add this joint chain saw model in its own tool program as well. Stihl chose to fit the E15 with a 40 cm bar as standard, but AEG showed better respect for the “1+1 hp for 25+10 cms bar” rule, so settled on a 36 cm bar. The AEG equivalent of the E15 was named “KES36” (KES is the abbreviation of “Kettensäge”).

So there you are. The E15 is indeed single phase, it has a brush motor derived from an angle grinder and the fittings in the hind section are brush caps. There are air intake louvre slits in the black hind grip and there are fan exhaust slits underneath the gear box and also exhaust holes in the upper part of the gear box, blowing air in a forward direction. This array is relatively standard for all large angle grinder types. The E15 is 60’s technology, so there’s no brake or clutch. The oiler is automatic, with the pump and the oil reservoir both integrated in the orange sprocket cover. The pump is driven by a crank pin stuck in the sprocket locking nut, which turns round a tranverse rod in the pump’s axle. The pin and transverse bar provide a sort of cardanic system, to compensate for any misaligned mounting of the sprocket cover. This is the same oiler setup as used in the E30, but that pump has a larger debit because of the slower rpm of the E30 (2800 instead of 6600 rpm).

The E30 has a .404”/1.6mm chain, the E15 is laid out for 3/8”, but i believe .325”-sprockets were also available for it. It is okay to use 1.3mm chain (the motor cranks out 1.5 to 2 hp max) but 1.1 mm is too thin, since the torque under severe load is much higher than that off small petrol Stihl saws fit for 1.1mm chain. The E15 had no soft start / current limiter provision like the relay in the WSA1900, since the spun up inertia of drive train and chain is less than that of a 6mm grinding disc, so the startup current peak of this saw is briefer and slightly less severe than the peak of an angle grinder. Seen from the side, the gear box of the WSA1900 has a somewhat bulbous humpy shape, which was no problem for grinding down welding seams or cast parts irregularities. Later versions like the WSA1700S and WSA2300 had very flat gearboxes to work in difficult angles and tight spaces. But seen from the top, the WSA1900’s gearbox is relatively slender, so it contains a rather compact crownwheel gear for such a powerful machine. This was done to have maximum use of the motor power and cutting depth of the disc. The small gear array of the WSA/WSB1900 range was also its weak spot. The gears were more than enough for a chain saw, but wore quicker than what was wished for in an angle grinder. Therefore there are many E15’s left over in working order today, and not many grinders. The grinders could become quite loud when the gears were in lack of grease or grew worn. The E15 can get loud as well, since the alloy frame, sprocket cover and bar all transmit the reverberations and tend to asmplify them a bit. This was one of the reasons for Stihl to choose glass fibre reinforced nylon gears in its E20. Even if nylon gears are in lack of lubricant or wear down and have their teeth deformed because of it, they remain relatively quiet, contrary to metal gears.

The E15’s production was ceased by Stihl around 1982. The E30 and E15 in the comparison pics were both built in 1981. The choice of an angle grinder as a power source naturally made this saw an inline-design, but the E15 was no novelty in that department. Many early saws, petrol and three phase alike (by Dolmar, Stihl, Mafell, Ural, McCulloch and many others) used beveled gear drives, with the motor mounted inline at the back. Many inline-machines were two-man operated.

I added some more E15 pics, revealing more of the motor itself. It is an earlier version built in 1975, when the rear handle of the AEG grinders was still grey instead of black. The small pic is from the Ebay auction through which I bought it and the large pics show both sides of the saw after being restored. The Duromatic bar in the pic came with it, but it is too large and too modern. I left it on to show the seller how the machine looked now and that it was in good hands, but i replaced it by a plain brushed steel vintage Stihl bar with black and orange print, as soon as i found one new on Ebay. Another detail difference is the logo. The newer 15’s have the orange rectangle, the earlier versions have the treetrunk cross section shape bolted on top. I don’t believe i’ve ever seen plain aluminium plates with “E15” printed in black, bolted onto the side of an E15’s orange sprocket cover. I’ve only seen cast lettering on both versions, painted in silvertone on the old models and in black on the newer ones. There is also a pic below with an E15 along with a KES36. There’s no KES in my collection yet, these models are quite rare ande well preserved ones even moreso. I have a WSA1900 in a box somewhere, which is not yet restored. I'll try to find it and when i have, will post pics of it in this thread.

till soon & all the best

gerhard

That E15/KES35 design is, from a mechanical engineering perspective, a thing of beauty.

I especially like the lateral thinking involved in adapting the grinder's castings to accommodate a left handed low RPM chainwheel drive and how the oiling mechanism is located and driven from within the sprocket cover.

It's not realistically the best place to site it, as it could interfere with the bottom scarf cut when falling timber by fouling the ground or other low obstructions. Nevertheless, you have to admire the sheer engineering genius in the design adaptation!

In my youth I had an old Ducati motorcycle which had a wonderful but ridiculously complicated shaft driven overhead valve mechanism that used bevel gears in the cylinder heads to turn the camshafts to both open and close the valves. Instead of using closing springs, as every other four stroke motor in the world does, these old V-twin motors had a single cam with an additional pair of wierdly ground lobes and double "Desmodromic" rockers to provide a truly mechanical solution. Afficionadoes of these bikes always remarked on the stirring exhaust note of a Desmo Ducati at speed. Personally I much prefer the mechanical symphony of the induction slurp, exhaust thump, the whine of the bevel gears and the rhythmic clatter of the tappets and rockers of a Desmo V-twin at idle.

I still feel that an inline design is a superior layout for saws of all descriptions. Those worm drive framing saw designs so beloved by our North American brethren are yet another iteration of the principle. It's obviously a more complicated and expensive matter to turn the drive through ninety degrees by using bevel gears and pinions, but also a superb engineering solution to gear down a high revolution motor into a slower revolving output shaft.

I've just purchased another new (old stock) E220C at a pretty good price, inclusive of the regulation 2 years warranty. Interestingly, this is marked on the ID plate as a 2003 build, meaning it's been on the shelf gathering dust for some 9 years. It still has the coasting brake of the later MSE220C models, and appears superficially the same.

One thing that I've noticed, however, is that the trigger actually has 3 positions: on & off (obviously) and a third, intermediate position that actually disables the coasting brake, allowing the saw to "run down" in the same way as my 3 faulty saws have done. This feature, while not exactly explaining why my coasting brakes have failed in the previous saws , does perhaps rationalise the additional wiring contacts you've shown attached to the trigger mechanism.