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Dangerous Ultrasonic Cleaner Electrical Failure

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Clive Foster27/07/2018 11:45:25
3630 forum posts
128 photos

A broken Ultrasonic Cleaner arrived yesterday for me to fix if possible. One of the common, inexpensive, but effective Chinese PS-20A heated variety as shown in the first picture. This one managed to clean two carburettors before it went pop. On contacting the supplier they simply sent a replacement suggesting that premature failure was not uncommon.

3) cleaner front view.jpg

Opening it up revealed a horrifyingly dangerous assembly error. The ultrasonic transducer drive board had been installed under the nylon stand-offs  rather than on top so many of the through hole connector tails on the PCB were firmly touching the metal baseplate rather than having a safe air gap. How the heck it ever managed to work at all I don't know. Would have expected major short circuits all over the place and instant failure.

2) board mounting.jpg

Looking at the board the only obvious damage is a an exploded capacitor and comprehensively blown on-board glass fuse. First time I've ever seen one with the end completely blown off. There is a space for a diode too but I suspect that was never fitted on this model as there is no evidence of it anywhere.

1) board top view.jpg

If you have a cleaner of this type it might be prudent to take the bottom off and verify that all is safely assembled. The fact that this one managed to work a couple of times despite what should have been instantly fatal issues suggests these things can be very robust and might well soldier on for considerable time with less major issues.

This one was made by Yi Bal Trade Co Ltd.

4) cleaner rear view.jpg

Clive.

Edited By Clive Foster on 27/07/2018 11:46:59

john swift 127/07/2018 12:02:42
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318 forum posts
183 photos

 

I suspect your the second person to look inside !

Some one else has had it  apart and not reassembled it correctly

 

John

Edited By john swift 1 on 27/07/2018 12:03:18

Brian Oldford27/07/2018 12:09:27
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686 forum posts
18 photos

I wouldn't like to say who or when someone has looked inside it. An ultrasonic cleaner is an item I've toyed with the idea of buying for a while. If I do buy one of these I'll certainly check it out before applying power.

Thanks for the heads up. You may have save myself and others a whole heap of grief.

Clive Foster27/07/2018 12:37:01
3630 forum posts
128 photos

Normally I'd agree that its been looked at before, and not put back together correctly. However in this case I know that's how it came from factory. Even if Paul had taken the board off there is no way he'd have put it back like that. That guy could give could give Inspector mMeticulous lessons! Anything electronic he has issues with ends up on my bench and he knows rules 1 to 900 are "Don't fiddle.".

Clive

Martin 10027/07/2018 12:48:13
287 forum posts
6 photos

Yes something quite visible that could indeed prove fatal. One would that with the 3 pin inlet and the metal case it is properly earthed.

I've seen quite a few glass fuses vaporised, the tails and end caps of the solder in type often being the only evidence left.

I would hope most if not all would recognise that method of construction as a major issue but as shown many moons ago on here a simple mains USB power supply feeding a seemingly 'harmless' LED lamp 'at 5v' has the inherent potential to kill because some USB power supplies, usually offered into the market by backdoor suppliers are, by design, built with near zero separation and are thus totally incapable of meeting any safety standard recognised in the UK/ Europe/Australia/USA.

Bazyle27/07/2018 12:50:46
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6956 forum posts
229 photos

Have you informed trading standards - This is probably just one assembly operator who made a dozen wrong before the supervisor noticed but didn't bother to recall the earlier units as he would have got a rollicking for not training the operator properly.

peak427/07/2018 12:54:40
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2207 forum posts
210 photos

Cheers Clive, I've been looking at buying one of these myself.
I'll check it out before plugging in if I do.

Bill

Neil Wyatt27/07/2018 14:04:03
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19226 forum posts
749 photos
86 articles

>ouch<

I sincerely hope you paid attention to the 'admonition'. I'd suggest calling Miss Li to complain, but you might expire before you got to the end of the phone number.

I note it has 'CE' in roman script, not a proper CE mark...

It can only be the curve in the board that let it function for a while.

Neil

Cornish Jack27/07/2018 14:22:45
1228 forum posts
172 photos

VERY interesting!! I've just (yesterday) disposed of that self-same model, having blown the fuse, opened it up, had a look , brain hurt and retired it to the rubbish bin - the cleaner, not my brain - although ...?. My dullard level of electrickery knowledge can work in my favour!! Being of a miserly and 'magpie -ish' bent, I 'rescued' the kettle socket and switch and the stainless bowl for possible future use.

Thank you, Clive

rgds

Bill

Michael Gilligan27/07/2018 15:47:56
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23121 forum posts
1360 photos

Thanks for the story and photos, Clive

Products are cheap ... Life is cheap

That's the world we are making for ourselves.

MichaelG.

.

[sorry ... feeling more cynical than ever, in this weather]

Edited By Michael Gilligan on 27/07/2018 16:10:21

Ady127/07/2018 15:51:56
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6137 forum posts
893 photos

Been thinking about one of these for a while, thanks clive

PS you might have just saved about 25% of the posters on this forum !

jaCK Hobson27/07/2018 16:03:40
383 forum posts
101 photos

I have been a fan of cheap goods from Ebay and BangGood but some recent experience have made me wonder...

I bought one of the cheap blue demagentisers with the little red button. It really works but I left it under a notebook (heavy enough to activate the red button) for 5 minutes. It melted.

I bought a thermostatially controlled soldering iron which heats to 450C in 40 seconds... and left it on for 8 hours. It melted.

Luckily the melted plastic in these products has a very pungent smell.

I'm not completely put off but I would strongly advise that these bargains are only operated under supervision.

KWIL27/07/2018 16:39:21
3681 forum posts
70 photos

Neil,

CE is correct for China Export, which it obviously issad

Clive Foster27/07/2018 16:44:11
3630 forum posts
128 photos

Realistically there is no way of knowing how common an assembly fault of this magnitude is. The "Friday afternoon" or "someone not watching the new guy (or gal) closely enough" error will always be with us. Probably even after the robots take over!

Shouldn't have passed QC of course. Or, at least next person on the assembly line ought to have flagged it. In a perfect world. In practice there are plenty of operations where corporate culture makes it hard on the ordinary worker bee if they do what they ideally ought about this sort of thing. Your children going hungry 'cos you've been dismissed without pay is a darn sight closer to home than some faceless customer half a world away.

What worries me is that the device worked a couple of times with such a major problem inside. Usually the magic smoke comes out immediately if its that bad.

Clive.

Jeff Dayman27/07/2018 17:17:36
2356 forum posts
47 photos

I've seen a number of electric shock / fire incidents in industry caused by mounting PCB's next to sheetmetal parts with no insulating material between them, due to movement of the sheetmetal in use. Using plastic standoffs with a specific assembly order with nuts washers etc. virtually guarantees some assys will be assembled in the wrong order, even with 6 sigma quality control!

It would be a far safer and more foolproof for assembly to have the PCB snap fit or assemble (oriented only one possible way by PCB boundary and plastic features) with thread forming screws in a flame retardant plastic housing with a UL94 V-0 rating, then mount the plastic housing with separate fasteners to the stainless assembly. The mount fasteners need to be well away from the PCB fasteners or live components (creepage and clearance per UL and IEC stds). This approach might add a 50 cent plastic part at production qty's in Asia but would reduce risks dramatically. Add a snap fit cover to the plastic housing made of similar plastic to the housing for another 20 cents and the electrical shock / external mechanical damage to PCB risk is further reduced. Personally I'd happily pay an extra dollar for better electrical safety on a metal appliance or tool like the u-sonic gizmo.

SillyOldDuffer27/07/2018 17:55:16
10668 forum posts
2415 photos

I shall stir the pot!

This was obviously assembled by one of those chaps who believe elf and safety have gone mad. Reckoned it was smart to save time and effort by reversing the pillars. He's down the pub this very moment telling his mates what fools the designers are for not spotting such an obvious trick. Of course he knows nothing about electricity...

smiley

duncan webster27/07/2018 18:05:51
5307 forum posts
83 photos

An obvious example of the Dunning-Kruger Effect. Put simply 'the less you know the more you think you know'

Mark Rand27/07/2018 20:32:36
1505 forum posts
56 photos

When I rebuilt my Hardinge, the original Variac that fed the carriage feed motor, via a rectifier, was burned out (the motor was missing as well crying). I replaced the motor, the Variac and also the original selenium rectifiers with modern silicon bridge rectifiers. The new, correctly sized Variac didn't last very long, probably because the current in the original had been limited by the original rectifiers.

Anyhow:- I got a Chinee PWM DC motor controller and wired it in. It worked perfectly for a while, then let all its magic smoke out. Turns out that one of the PCB tracks ran right to the edge of the board and was close enough to eventually ground out on the case. The bad design could have been worked around with a plastic shield or a bigger case.

I bought another one and opened it up, expecting to need to insert a shield if the PCB was of the same design. Low and behold, this one already had a bit of insulating tape stuck to the case in just the right place!

I.M. OUTAHERE28/07/2018 07:02:53
1468 forum posts
3 photos

I have one of those cleaners and mine has 6 transducers controlled by three driver boards , i never really checked that all of the transducers were working when new but after a few uses i noticed a real drop in cleaning performance .

I took it apart to find two of the driver boards has died for some unknown reasom and both had destroyed the exact same components , i repaired these and changed the same components on the board that was still working and have had no issue since . The performance was better than when new so i would guess that at least one of the boards had failed in the first run .

Eric Arthrell28/07/2018 07:51:07
47 forum posts
19 photos

Under rated components, quarter Watt instead of half watt resistor insures a repair department.

The trick is getting It to fail just after 12months, then you can buy a new one or have it repaired ?

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