This error is show when the Bed does not reaches the required temperature as set by the machine. To confirm that the error is related to bed you can check the last word of the error which says "Bed".
This error comes when the bed does not get heated to the required temperature according to the temperature set by printer. The printer has inbuilt program which monitors both the temperature and power supply to heating elements. So when certain temperature is set, the printer starts supplying power to the bed heater and takes the temperature reading using thermistor. If the temperature does not increases after certain period of power supply to bed heater the printer detects a issue and stops.
This error can be caused by 3 issues.
1. Faulty Thermistor.
2. Faulty SSR.
3. Faulty Bed Heater
4. Wiring Loose connection.
Min Temp error for bed-
1. Take a multimeter and check the resistance of the Thermistor. If the thermistor is giving incorrect readings then thermistor is damaged and needs replacement.
Remove the thermistor wire Check the resistance on the Resistor. Resistance should be around 90 Ohms else
If the thermistor is giving correct readings then the wiring is faulty. You need to check the wiring of the Thermistor till MKS. There will be some connectivity issue which will hinder the transfer of thermistor data to MKS. Fixing the connection will solve the issue.
1. Check power supply to SSR:
SSR is the component which supplies power to the heater bed for heating. If the wiring from power switch to SSR is damaged the the SSR and Heater bed will not get power supply.
How to check?
Take a multimeter and check current at SSR input (for neutral probe use the neutral wire in Power switch of SMPS). If the input is not there then check for loose connections near power switch. If the input is correct then check the the output terminal of SSR.
Incase the supply is correct the Voltage should be around 220V
Note: The line input and line output can be interchanged as there is no polarity. SSR just creates continuity which starts current supply to Bed
Checking working of SSR:
If the Bed heating is turned on then the SSR output should be 240 Volts. If the bed heating is not on then the SSR should not be supplying any current
In case of faulty SSR the SSR will supply or not supply current irrespective of the bed heating state.
If the SSR is not switching between on and off WRT to bed heating status the SSR is spoilt.
Check the other pin, use the SMPS neutral for probe.
For confirmation check the MKS output terminals.
When the bed is in heating state the MKS bed heater terminal should output 24 volts. When the Bed is not heating the output should be Zero.
Note: There are chances of MKS not giving commands to SSR for switching. So before confirming that SSR is damaged do a confirmation test by checking MKS output.
Start bed heating and check the voltage. It should be 24v or 12 V
If the MKS outputting 24V or 0V irrespective off ON OFF status then MKS is damaged and SSR is not functioning since MKS is not giving it input. MKS needs to be Replaced if MKS is faulty. If MKS is fine and SSR is not functioning properly then SSR needs to be replace.
If both SSR and MKS are working fine then Bed heater will be faulty.
To check if Bed heater is faulty you should check the resistance of the bed heater. Take a multimeter and connect to the terminals of Bed heater. The resistance should be around 100 ohms. If the bed heater is faulty the resistance will not be shown correctly.
Remove the wire connected to bed heater. Remove the neutral wire from SMPS to get correct resitance. Check the resistance of heater Bed using line and neutral points. The resistance should be around 140 ohms
To confirm that it is bed heater damage and not wiring issue, cut and remove the solder of bed heater wire and check. If the resistance is shown correctly when you connect directly then the wiring was faulty. So replace the wires and solder new wires. Or else bed heater needs to be replaced.