On 02 Jul 2020 14:17:34 +0100 (BST), Theo
wrote:

Archibald Tarquin Blenkinsopp Esq wrote:
From the rear.

1. Mains in 6. ALM
2.Mains In 7.ALM
3 Common 8. RT
4. SSR+ 9.TC-
5.SSR- 10. TC+


6 I strapped to 1, with 7 taken to a 240Vac relay

Hang on a mo. According to a different datasheet:
https://www.mpja.com/download/rex-c100.pdf

Power input is 6 and 7, alarm relay contacts are 1/2.
Thermocouple 8/9 or thermistor 8/9/10, output 4/5, 3 can part of alarm or triac output.

If you put the relay contacts 1/2 across the mains that might explain
things...

Of course, in the Cambrian explosion of clones who knows how yours has
evolved.

Much testing and head scratching later, I dropped in my last
controller which unfortunately has no alarm relay.

It works!

Did these all come from the same vendor?

Theo
It is tempting to think that I might have been in error at some point,
my sanity wouldn't be at risk if it were mere incompetence :-).

If you look at the image you originally sent though, the sticky label
suggests pins 1 & 2, if you then follow the image to the last PCB
layout, the photo shows the mains input bits clearly going to the
lands labelled 1 & 2. If you then look at the PCB layout and the case
accommodating the PCB, it has to go with the lands connected to the
thermistor, bridge and resistor to terminals 1 & 2.

Although in the case of your drawing, my thermistor in series with the
mains input becomes a transorb, which although difficult to see the
connections must be across the resistor feed to the bridge.

I do not think all three came from the same vendor. My third working
one would have been a trial to see if the bargain was too good to be
true. :-)

The two faulty ones would have been for long term use, one being the
spare.

Hence the relay out function on the service units, as protection
wasn't an issue for the trial [that never happenned, incidentally].

Anyway thanks for the suggestion, I must admit this one has me
flummoxed.

AB
From the well pummelled keyboard of Archibald Tarquin Blenkinsopp Esq