Help Needed Please! Electric Machine Fault.

[AES]

Scroll Saw knowledge NOT required (I don't think so anyway)!

A) I have an Excalibur EX-21 CE Scroll Saw. It requires 220/240 V and draws 1.5 Amps (manufacturers data);

B)The motor, a fully enclosed type, is 60 V DC, variable speed (external control knob);

C) Unlike UK versions of this machine, mine does not have an NVR;

D) I am in Switzerland. Our electrical plugs are different to UK plugs. Biggest difference no fuse in the plug itself (but the workshop mains circuit supplying the machine IS fused - a CB actually);

E) The machine is fitted with an accessory On/Off foot switch (NO speed control in foot switch);

F) Also driven from the same mains supply; vacuum cleaner; work light (separate mains plugs);

G) The machine now 8+ years old; generally recognised as being very much at the high quality end of the market. Has never suffered any sort of failure electrical or mechanical before - until yesterday!;

H) NO changes whatsoever to the above set up in the whole 8+ year period.

Yesterday's job was well within the usual "hot knife/butter" capability of this machine. Brand new blade; low speed; cutting a "doughnut" from soft ply (NOT Baltic Birch), approx 10 mm thick.

PROBLEM:
In middle of job machine suddenly stopped with a loud "crack" sound (similar to a blade break sound - which it wasn't)! NO smoke, NO smell, NO flames! NO blown mains supply CB either.

CHECKS ALREADY MADE:
A) Changed machine fuse (AFTER finding it on machine)! Fuse 5 Amp clear glass cartridge type. Removed fuse obviously very "kaput" (blackening of fuse itself and surrounding fuse holder area. One metal end "blown off" fuse). Machine still completely dead after cleaning fuse holder then fitting new spare fuse;

B) Within available mechanical limits, motor still freely rotates cam mechanism;

C) Removed foot switch; work light; vacuum cleaner from supply - one at a time, then all together. Tested machine each time. NO GO;

D) Checked one motor brush. "Perfect" condition; smooth commutator contact surface; virtually same length as new spare brushes; NO sign of carbon dust on brush/around brush holder area. (As motor is fully enclosed not possible to see arcing etc from commutator. But no funny noises or smells ever noticed throughout machine life).

QUESTION PLEASE:
From the above symptoms and checks, I now strongly suspect a "blown" PCB ("Motor Control Panel" - the manufacturers description). Agreed?

Though "simple", this machine has a lot of mechanism packed into a very condensed area, and at a guess it would take a couple of hours careful work to remove the PCB and replace it with new (which I would have to order).

My worst case scenario would be to spend the dosh and time to replace the PCB only to find it's not the problem! SO:

QUESTION PLEASE:
Is the any other check/s I could make before ordering a new PCB? It so how please (I have limited electrical/electronics knowledge).

TIA

 

[MorrisWoodman12]

I have no direct knowledge of this saw but have mended the PCB on a couple of variable speed lathes so a bit of experience with similar systems.
Does the incoming mains supply connect directly to the PCB? If not what is it connected to other than fuses and switches?
Do you have any way of safely measuring the 220/240 VAC mains so you are sure it's supplied to the PCB? EG. a meter.
Do you have a car battery (12V or preferably 24V). I suspect if the motor is connected to it the motor will turn albeit slowly and with little power - you may need to disconnect the load/cam mechanism. That will give confidence in the motor and point further at the PCB assuming the PCB is getting mains supply.
Hope this helps.
Martin

 

[Sideways]

That sounds like a pcb failure or a dead short in the wiring (a wire gets pinched and over time the insulation is gradually squeezed out until two wires short out or a live shorts to earth. You'll be able to see it ...
The advice about the motor is good.
Universal brushed motors will run off ac or dc and if it is rated 60V dc, then it should turn slowly if you apply 12V or certainly 24V from a car battery or a car battery charger directly to the motor.
If you heard a "crack" then you should be able to spot the failure if you look hard enough. Discoloured component / pc board / blown section of track / wire and when you open it up do try the smell test again

But first of all, make sure the fault isn't inside the mains flex so disconnect that where it enters the machine and carefully check it with a tester.

 

[ajs]

Again, no direct experience of that model but looking at the manual and the wiring diagram it looks like a PCB fault, there isn't anywhere else it could be, mains in the to board and motor drive out. My hunch based on the symptoms is a blown cap in the rectifier, yes that will mean getting to the PCB but in the plus side it will be an easy visual inspection. Back of an envelope calculations suggest several thousand microfarads which at 60V+ will be physically quite large cylinders, if there's only one perhaps a couple of inches long by an inch or more diameter, correspondingly smaller if there are several making up the capacitance. In they are bulging out or in particular if the end cap is buckled outwards or even missing that's a failed cap, they'll usually be liquid residue around too.

If that's the case I'd suggest pricing up a new board but if you feel capable a board level repair shouldn't be too difficult. Finger in the air pricing suggests new caps could be anywhere from perhaps £4 - £35 here in the UK, yes that's a big range but there's a lot of scope for variation in precise values. I'd probably opt to replace the rectification diodes/bridge rectifier at the same time - perhaps £2 tops. If I'm right and you can post some good photos of the board we can probably advise further.

 

[AES]

@MorrisWoodman12; @Sideways; @ajs:

Gents, thanks a lot to all three of you for your prompt and very helpful replies. Though I spent a LOT of time last night Googling for similar problems on this machine, I found nothing relevant! And it was "only" your input Morris that made me even think about (!) doing another search for a circuit diagram for this machine (there's nothing of the sort in the Manual I got with the machine). The result is attached below. But first, answers to all your Q's:

A) I don't have a meter suitable for poking about in mains (and even if I did, I "know" enough about electrics to be sure I should NOT be trying that)!

B) From physical inspection (VERY difficult, needs work light, good torch, and a mirror!) it looks like the mains lead does go straight to the PCB.

C) The attached "circuit diagram" (more of a "schematic", surely?) seems to confirm item B) above.

D) To give those unfamiliar with this machine I have included a Parts Diagram (plus key) to give an idea of the access problem. It's one of three diagrams - so it's a "complicated/tightly packed" machine. Example: There's no way I can even see - let alone remove - the PCB without substantial dismantling.

E) Mainly to help other Excalibur owners I have also attached one page from a rather better Manual which I found during the online search this morning. As per my OP, it took me a LONG time to even find the fuse holder so it MAY help other owners.

Gents, in the light of the above PLUS your inputs, the consensus seems to be "Get yer tools out and buy a new PCB AES!" AGREED?

AND, unless it's a "simple" single layer PCB requiring only "simple" soldering I doubt I would be able to repair the present PCB, even if it is "only" a capacitor.

QUESTION:
Any ideas as to what "AC1" and "AC2" as shown on the circuit diagram are please?

Again, thanks all. One really can rely on at least one person on this Forum knowing the answer to just about any Q

ATTACH FILES:

(To follow on as a PS as soon as I've scanned them).

PS for attach files:
1. EX-21CE Circuit Diag:

2. EX-21CE Parts Sheet A:

3. EX-21CE Parts List:

4. EX-21CE - Mains Fuse Location:

I think that's it. Thanks for all help Gents. Looks like I'm off ordering a new PCB (?) and getting the tools out. JUST what I need right now. NOT!

Cheers

Another PS - SORRY.

I have done a simple continuity test (1.5V bulb!) on the mains leads. All OK

 

[Sideways]

A quick cut n paste for convenience

1)AC1– Non-inductive or slightly inductive loads
2) AC2– Starting of slip-ring motors
3) AC3– Starting of squirrel-cage motors and switching off only after the motor is up to speed. (Make Locked Rotor Amps (LRA), Break Full Load Amps (FLA))
4) AC4– Starting of squirrel-cage motors with inching and plugging duty. Rapid Start/Stop. (Make and Break LRA)
5) AC11– Auxiliary (control) circuits

A switch, contactor or relay has a different current rating depending what use it is put to. Starting and stopping resistive loads is easy so the switch will be rated for most Amps in AC1 duties.
Frequent start,stop of inductive loads like motors means big surge currents for a large proportion of the time, so the switch is derated to smaller number of Amps.

For your purposes it's probably irrelevant unless you need to replace the labelled component, in which case get one with the same AC1 rating. Universal brushed motors are generally considered "resistive" loads. Not like induction motors.
In fact the switch sees the PCB not the motor directly, but it will still be much closer to a resistive load than anything else so AC1.

But.
This is the general use of AC1, AC2, etc

When you paste the cct diagram we may find them using the terms just to arbitrarily label two terminals of an AC connection because the circuit doesn't care which is live and which is neutral. In Europe it doesn't really matter because the plugs aren't polarised.

 

[MorrisWoodman12]

AC1 and AC2 are just arbitrary labels for the two AC mains connections.
When you did the continuity test on the mains lead did you check there was no connection between the live and neutral leads between the mains input/fuse holder and the PCB? A 1.5V bulb is great for this type of test.
Let me know if the cost of a replacement PCB is too horrendous: I may be able to look at it if you send it to me.
Martin

 

[AES]

Thanks again Morris (sorry, Martin).

Because my electrical "knowledge" is so basic, yes I did check all three "prongs" on the plugs and the "sockets" on the other end/s. I also had the foot switch "in circuit" with my foot on the pedal!

(Long ago I made up a little dry cell battery holder with a torch bulb holder and a couple of leads with croc clips on one end and "thin probes" (bits of piano wire actually!) on the other ends.

So yes, I'm quite happy that the whole mains lead assy from plug in the wall until the electrons arrive at the machine is all OK.

BTW, the total length of the mains lead assy, inc foot switch, is only about 2 to 3 Metres, and it's good "thick" rubber coated mains cable which is not subjected to undue vibrations, wear & tear, etc.

(SOOOO: It IS that "+"*ç%&/()=" PCB, isn't it)? It's really all it can be?

And thanks for the offer of repair. I have to wait until tomorrow anyway to order a replacement PCB, and I've no idea what the delivery time is. So with that AND all the disassembly required, I'll wait until I can actually even SEE the PCB before deciding what comes next.

But thanks a lot, despite the horrendous Post charges here I may well take you up on your generous repair offer - beer tokens and post charges included of course!

 

[AES]

@MorrisWoodman12:

Further to the above, if everyone else agrees that it IS the PCB, once I get it out of the machine, I will be vising UK in mid Nov for personal reasons. So that MAY nullify the stupid Swiss post charges, not to mention possible duties.

Yes, we're getting ahead of ourselves (or I am), but it may well be sensible to continue this discussion by PM if going that route? (Again, assuming that everyone agrees it's the PCB, and even with my limited "knowledge" I really can't see anything else).

 

[Skeety]

Hi,

From reading your description and the above posts I would concur that it is most likely the PCB.

However, going with the Capacitor theory (which i agree with) the thing that counters that is that you had no smell, normally electrolytic caps stink like fish when they let go.

Have you been aware of the motor speed surging at all, not staying at a constant speed?

Another thing that PCB's in this type of use are prone to are dry joints\broken joints. You could try some gentle taps of the machine with the power disconnected and see if it comes to life at all when the power is reconnected. If that is the case then you or someone local could just go over the PCB and re-solder the joints.

I did find this article which seems to relate to the same saw as yours with some pictures of the PCB. For a simple speed control there seems to be quite a bit going on, feedback from an optical sensor on the motor to maintain speed as load is applied. Several different TRIACs etc. One of the sticking points seems to be their is an IC (Chip) on the board which is covered in black epoxy making the identification difficult.

Would be good to see some pictures of the PCB once surgically removed.

Article i found is here: https://maker.pro/forums/threads/defective-pcb-scroll-saw.275695/

Cheers,

Jon.

 

[AES]

Thanks for your inputs Jon. Much appreciated. To answer your points:

Though it's not a completely sealed compartment, the location of the PCB is such that I doubt I would have smelled anything short of a total eruption in there! It's about as far from the "operating position" as is possible to get while still cutting; I wasn't wearing a face mask; and I smelled nothing at all at the time of the "crack" sound.

These machines are noted for their lack of vibration. Mine is bolted down to a thick ply top which is firmly screwed down to a "typewriter desk" (sheet steel fabrication); the "desk" is on castors, but apart from the odd movement around the shop (sometimes for access to other stuff - it's a smooth concrete floor) nothing is subject to any other sort of regular movement or vibration.

The motor speed has always stayed constant as set on the pot and has never given any sound to indicate labouring - not ever - not yesterday before the "bang" either. And I've cut some pretty horrendous stuff on it in the past - using bits of broken band saw blade which IS "allowed" in the machine Manual - with never any indication of any loss of speed or power on the blade.

With the above in mind, and with respect, I doubt that any amount of "tapping" on the machine outer casing will reveal any dry solder joints, etc.

Thanks very much for the PCB photo. Useful, at least for "my EX-21 file". I'll now do a search for any disassembly instructions on line.

From all the following it looks like you WILL be getting photos of the PCB once it's removed! "Don't hold your breath" though

Cheers

 

[MorrisWoodman12]

Some observations re @Skeety 's post.
IMHO dry/broken joints usually cause malfunction (e.g. full speed or not running) rather than blowing fuses.
The only connections to the PCB other than incoming power and the motor are to the speed control pot(entiometer). This is designated VR on the parts list and there is no mention of an optical sensor separate to the PCB. Of course this can be built into the motor but there are only two connections (power and return) between the motor and PCB.
Yes it will be good to see a photo of the board once it is extracted.

 

[amakah]

If you know little about electrics get somebody who does know have a look at it.

 

[Spectric]

Why do these scroll saws all seem to use low voltage Dc motors, why don't they just use a brushless Dc motor and controller running 230 volts Ac. Easy to control speed and set motor characteristics.

 

[AES]

Why do these scroll saws all seem to use low voltage Dc motors, why don't they just use a brushless Dc motor and controller running 230 volts Ac. Easy to control speed and set motor characteristics.

A rhetorical question Spectric?

If not, then I have no idea, sorry.

 

[johnwalls26]

Just a thought, is the year of manufacture shown? In the early years after the change to lead free solder, manufacturers continued to work at their usual temperature before the need to work at higher soldering temp for the new solder was apparent.

 

[AES]

Yup, maybe John.

But machine was made in Taiwan (under licence to Canadian company General International), so "maybe" with other countries involved, "lead-free solder" rules not relevant?

In any case, with my admittedly limited knowledge, IF poor soldering was applicable then I would expect "dry" solder joints fault/s would have shown up long before, when the machine was first bought 8 years ago? Especially in a low-vibration environment?

But thanks anyway.

INFO TO ALL INTERESTED:

PCB (and spare fuse!) price and delivery lead time now being investigated through the seller (Dictum Tools in Munich). Will advise further.

Cheers

 

[Spectric]

A rhetorical question Spectric?

Not really, we see quiet a few issues with these scroll saws from various OEM's and they all seem to use these low voltage motors with speed control and often the pcb is at fault. What is the design reasoning behind this approach, I initially thought cost but when you can get an electric scooter for £150 that uses a brushless Dc motor with field orientated control then how much is just the motor and controller ? It would not be hard for an OEM to make big improvements but I think they are just sticking with the technology they have always used and are not looking to change. Then looking at the OP's problem the control board seems to be a weak link and again there is no reason not to have more protection so the board is more robust but again selling boards is probably profitable. When I look back to when I made a coil winding machine I just took the easy approach, this would also work on these scroll saws and that solution was to use the pedal control from a sewing machine.

 

[AES]

Not really, we see quiete a few issues with these scroll saws from various OEM's and they all seem to use these low voltage motors with speed control and often the pcb is at fault. What is the design reasoning behind this approach, I initially thought cost but when you can get an electric scooter for £150 that uses a brushless Dc motor with field orientated control then how much is just the motor and controller ? It would not be hard for an OEM to make big improvements but I think they are just sticking with the technology they have always used and are not looking to change. Then looking at the OP's problem the control board seems to be a weak link and again there is no reason not to have more protection so the board is more robust but again selling boards is probably profitable. When I look back to when I made a coil winding machine I just took the easy approach, this would also work on these scroll saws and that solution was to use the pedal control from a sewing machine.

-----------------------------------------------------

OK, I understand your question but doubt that I'm able to answer fully.

First I wasn't aware that "all" scroll saws use such motors, just that mine and "some" others do. (So do the very common Chinese Mini Lathes BTW)

Second, my machine was originally designed and produced in Canada in, I think, the 1980's or 90's. Were brushless motors "commonly" available then? I dunno.

Third, since the start of that machine numerous developments have been made, mostly (AFAIK) to the mechanicals. There have also been various changes of actual manufacturer, with the manufacturing being moved to Taiwan some time ago. Nevertheless that machine has retained it's "high-spec/high-value image" and is today generally reckoned at least one of the best on the market throughout the scrolling world. It's certainly pricey, like the equally highly-regarded Hegner, and (IF you can find one outside the US) the Delta machines too.

Fourth, perhaps the design and production of my machine is covered by patents, etc? I don't know. But what is clear is that when production first moved to Taiwan there were quality problems with some first batch machines and apparently the original "design rights holder" (for want of a better title) sent someone to Taiwan to sort the problems out - which were indeed sorted.

I do take your point about the PCB on my machine apparently "blowing up" because the machine was expensive enough 8 years ago (circa Euros 700) and today what is AFAIK the same machine costs about Euros 1,000! So I wouldn't really "expect" to have such a major problem on a machine at that price level (at least major as far as gaining access to the problem is concerned).

But as said, PERHAPS (I have no idea) the current manufacturer of this machine is "not allowed" to much such changes? Again I just dunno.

Finally re your point about selling spares. I currently have an enquiry in re cost and delivery time of the PCB. I don't yet know what the answer will be, but one important aspect which differentiates my Excalibur and the Hegner machines is that Excalibur spares prices are definitely much more reasonable.

As above, I'll post the price and delivery quote here once I have the answer so all interested know.

Thanks for your interest.

P.S. Re the Chinese Mini Lathes mentioned above. I THINK that the newer models are indeed brushless electronically controlled motors. Mine (an older model metal lathe) has a DC motor controlled by a PCB which I HAVE already had to have repaired. So your basic Q does indeed make sense. Perhaps these manufacturers are just "slow"/have too much invested in "the old ways"???

 

[Sideways]

If I had one and it were to fail in this way, I would be open to alternative solutions.
A 60V dc power supply rated for perhaps 8 Amps is the first requirement. These can be found on ebay from various sources. Switch mode power supply modules designed to power stepper motors or (commercial more likely than domestic) LED lighting are fairly plentiful. Meanwell is a very reputable Chinese brand for these.
Then you need a DC to DC variable voltage module with at least the same maximum voltage and current ratings as the power supply.
The type needed is often termed a "buck" converter. Buck being a converter that outputs less voltage than you feed into it, Boost being the opposite, a converter that provides an increased voltage but at a lower current.
Feed the power supply output into the variable voltage module and the variable voltage output straight into the motor terminals and away you go.
These modules are likely to be bigger, more robust and less prone to overheating than an all in one circuit board squeezed into a tiny compartment in your saw with no air circulation.

Here's an example of a 60V power supply (500W) I picked up unused on ebay for about £50

And here is an extreme example of a "buck" converter.
This RIDEN RD6018 module is rated 60Volts, 18Amps and basically lets you turn any spare DC power supply into a very usable laboratory power supply. It's far too much overkill for the job but the point is that this level of tech costs about £100, so I imagine a simple 60V/8Amp+ variable output buck module can be bought for considerably less.

(In case anyone wonders, I've fitted this module into a mini systainer fed from an old laptop power supply. It makes a great charger for the car battery and happily bangs out 9A for hours on end).

When @AES posts a picture of his circuit board, it will be interesting to compare how much "tech" you can buy for the price of a replacement board.

The good news is that with simple and readily available modules, it doesn't need much knowledge to make a functional replacement for a PCB on an old machine or a no name machine where the supplier has gone out of business or doesn't offer spare parts.