I was using my old Bosch PST-50E 'electronic' jigsaw yesterday, and I
noticed the handle seemed rather warm. Then there was a flash and a
bang from inside, but the saw carried on as if nothing had happened.
No trips gone, no fuses blown (13A in the plug, probably way too high,
it's only 350W), variable speed still OK, no obvious RFI. So what
happened? I suspect a capacitor popped, but where, I don't know. I
don't particularly want to open it up to find out, as it still seems
to be working OK and I might not be able to re-assemble it. It doesn't
get much use, so I'm not in a hurry to replace it, and being plastic
and so-say double-insulated, with no earth wire, it should be safe
enough to handle.
It could be the suppressor capacitor across the mains, it'll not
affect the working of the jigsaw at all if it's not there. They are
'X' rated (I think that's it) for direct connection across 240v AC and
they're supposed to fail safely. If this is what happened I don't
think it failed all *that* safely! :-)
Some even fail benignly, aka "self-healing". The are a metallic layer on plastic
film, wrapped around. A local short-circuit due to overload causes an arc which
locally burns off the metal, leaving a pinhole with a non-metallized circle
So it goes bang, emits magic smoke, and continues working fine afterwards with
slightly reduced capacitance.
In fitting a new capacitor its probably best to get a spare, not a generic part,
because they caps tend to be wedged into place and need to have the "right"
shape for that. Waiting to replace it should be fine (until it happens again,
causes radio interference, warms up, smells, emits sparks, goes off and joins
the Foreign Legion, ...)
On Thu, 17 May 2018 12:18:20 +0200, Thomas Prufer wrote:
I'd have finished that with "and joins the choir invisible...". :-)
I had a similar experience a month or two back. I was sat at this very
desktop computer late one evening when I heard a very loud and distinct
bang of a major catastrophic HT component failure in an SMPSU. The
strange thing was that nothing seemed to be in the least bit effected
(and I had a few candidates plugged in and powered up in my 'Den').
My best guess for "The Event" was that it could only have been an X
rated filter cap that had gone bang (self healing or not) and, quite
possibly the one in the ATX PSU of my desktop computer (or maybe the one
in the ITX PSU in my Gateway 2000 desktop NAS4Free server box). Since I'd
only heard and not seen or smelt any other evidence, I just shrugged and
carried on, placing my trust in the non end user serviceable fast blow
fuses inside of metal cased smpsus to protect me from the risk of a fatal
conflagration, as if nothing had happened.
 Quite frankly, in the complete and utter absence of *any* failed
devices, I simply CBA to waste time trying to track down a blown filter
cap. Whether it had self healed was a matter of total indifference to me.
The important consideration in this case being that everything was still
functioning with literally no sign of 'magic smoke emission' nor any
unusual smell to suggest any further trouble brewing.
 Such an "Event" could have happened before whilst the 'Den' wasn't
being occupied. Such a scenario, "If a mains filter capacitor arcs over
internally and there's no one there to hear it, does it make a noise?",
reminds me of the other, rather more prosaic, 'Chestnut',"If a tree falls
in a forest... yada, yada, yada..." which begs the question, "Why
Well, if its got suppression capacitors then you may feel its not giving
rfi, but it probably is. Normally the switch and handle are not that bad to
get at. The thing to watch is the springs in the trigger if its the speed
control as well. You need to do the final cover removal under a plastic
bag, so anything that shoots out is caught.
Chances are its one of maybe three capacitors which has gone leaky and has
been a bit of a drama queen, and blown open circuit.Note, change all of
I've not forgotten my rectifier diode cheapskate repair of a video which
meant I had to change all four in the end as they died one after the other!
This newsgroup posting comes to you directly from...
On Thu, 17 May 2018 09:46:32 +0100, Chris Hogg wrote:
Had similar with my Bosch SDS drill the other day. Except that the
drill stopped, opened it up, (well designed no ping fuckits), and
found supression capacitor across the mains had ruptured it's casing
and the coiled up ali/plastic core damaged and exposed. Removed it,
reset the MCB, drill worked fine. Have have since replaced it with a
proper spare part from Miles Tool and Machinery Centre.
I guess if I'd just reset the MCB it may have just worked but I
wouldn't have known about the state of that capicitor...
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.