On 02/07/2020 01:29:55, Archibald Tarquin Blenkinsopp Esq wrote:
On 01 Jul 2020 23:45:55 +0100 (BST), Theo
wrote:

Archibald Tarquin Blenkinsopp Esq wrote:
I found a last one without an alarm relay unfortunately, it worked.
The only difference was a yellow caution sticker by the mains input.
Yet they were all ordered as 240V and it ctearly states 240V on the
case.

Does this sound familiar to anyone?

Not exactly, but I think there are a number of variations of the REX C100
clones and they don't populate all the components. Try comparing yours with
some of the teardown videos. For example this:
http://www.karosium.com/2014/11/rand...-c100-pid.html
looks like there's a chunky transformer included - is that missing from
yours?

Theo
(used one successfully powered from mains)

Thank you, it suggests that there may be an inherent problem as mine
blew on switch on too, both of them.

Mine has the transformer. The disk appears to be a transorb on the
photograph though, yet my device uses an NTC thermistor.

It is electrically similar though, the thermistor on mine coming from
the land labelled 1 on the photo, and the other land "2" is where the
resistor connects into the bridge rectifier. It,s a minature surface
mount unit on mine, not discrete diodes as in the photo.

It really is odd though, there is no sign of damage on the mains in [1
and 2], yet the amount of print that is stripped and burnt from lands
9 and 10 is unreal.

The second unit only had 1 and 2 connected to the mains and 9 and 10
were completely open, yet in both units 9 and 10 are splattered.

My theory that it was 24V was obviously wrong, in comparing the unit
to your linked photo I checked the capacitor fed from the mains input
in my unit it's 4.7 uf 450V, so it must be the Volts stated!

Oh well, I'll saw the outer case open in the morning there is
something damned weird about this.

Reminds me of a load of PIR switches I had, I fitted a fair few when
doing some DIY wiring, but for no obvious reason three blew, quite a
flash & bang and they never worked again, but I could find no evidence
of a short at all. All surface mount, so how something can produce
noise and light yet show no damage beats me.

Clever these Chinese :-)

I have purchased items that were sold as 240V but in reality were 110V.
The transformer saturates taking out fuses without any visible damage on
the primary side.

If you had a variac you might have been able to check function without
the light and smoke.