Duet bed heater problem

My ormerod worked great but I thought I would build a corexy machine for better quality prints.

I already had a duet v6 from repeko, bought some time ago. I fitted it to my newly constructed D-Bot but the Ethernet connection did not work.
So I removed the duet v6 from my ormerod which worked great in the D-Bot as far as being able to use the web control which I am used to.
During all of the setup I have had a -21 temperature on the bed heater temperature display which I just left to sort out later.
Later has arrived..
The bed heater connection on the ormerod was by ribbon cable but my new 200 x 300 mm heater requires a 2 wire cable. So I removed the bed screw terminal connector from the repeko board and soldered it onto the original ormerod board.
Connected the thermistor and heater wires and switched on.
If I activate the bed heater it seems to stay on for a few seconds and then goes into an open circuit fault condition. I checked the connections with a meter and the bed resistance is 1.8 ohms and the thermistor 115.4 kohms.

Do I need to do anything else to convert from ribbon to screw connections?

Any ideas what could be causing this?

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

You shouldn't need to do anything else apart from add the terminal block and thermistor connector. However, you will probably need a powerful soldering iron with a largish bit to get good soldered joints between the bed heater terminal block and the PCB, because there are large areas of copper attached to the holes for the terminal block pins, which will tend to suck heat away from them while you are soldering. If in doubt, connect your bed heater and then check its resistance as measured from the ribbon cable connector.

The bed thermistor on the Ormerod is 10K, but you have a 100K thermistor. So you will need M305 P0 T100000 in config.g.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

You are a star

I'll say it again

YOU ARE A STAR

I really should read the gcode guide more, my copy is way out of date. I was unaware that the T parameter existed, What is the B parameter for and how is it found or calculated?

My thermistor measured 115 k ohms so should T115000 be used or is T100000 good enough?

again thank you for your valuable help

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

Your thermistor is probably 100K at 25C, which is what goes in the T parameter. If you can't get any data on the bed thermistor and it is a generic Chinese one, try B3950.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].