Heater bed error

We’re still trying to get our mini back in service. Pretty much everything suspicious has been replaced including the board, all the wiring, and the heated bed. Now printing starts but stops with a Bed Heater error. We’ve reflashed the board several times. I’m stumped.

Here are a few lines of debugging code from the console when the error occurs.

< [13:26:38] ok N84 P1 B4
< [13:26:38] ok N85 P0 B4
< [13:26:39] T:232.81 /240.00 B:85.00 /85.00 @:70 B@:50
< [13:26:40] ok N86 P0 B1
< [13:26:42] T:234.22 /240.00 B:84.97 /85.00 @:89 B@:57
< [13:26:43] ok N87 P0 B2
< [13:26:45] T:236.25 /240.00 B:63.15 /85.00 @:73 B@:127
< [13:26:45] Error:MINTEMP triggered, system stopped! Heater_ID: bed
< [13:26:45] Error:Printer halted. kill() called!

Looking at the reported temps for the heat bed you lost ~20C in three seconds time. I would check the wires for the thermistor.

< [13:26:42] T:234.22 /240.00 B:84.97 /85.00 @:89 B@:57
< [13:26:43] ok N87 P0 B2
< [13:26:45] T:236.25 /240.00 B:63.15 /85.00 @:73 B@:127