ADVICE! Newbie builder - Its built but Filament doesn't lower

[Wal10s2018]

Hello folks
I am not a techy - just finished building I3 Pro B, (bought 2018 but just now built due to ill health) and have had a few teething issues which I have overcome. I cannot however, fault find and fix the fact that the filament isn't lowering when I try to do the initial auto home calibration. The motor takes it left and it hits the limiter (with black wires) the it should then travel down, to home start, but doesn't. I hear the motors turning and there is the start of movement, then it just stops. Manually I can turn both threaded rods and these do lower the filament head. LCD readout says - 'ready', and filament/hot plate both able to heat up.

I was very confused with instructions as it talked about various model numbers relating to PCB boards - and I just left it standard without making changes. How do I check that different model types? If I can move the carriage down manually - am I right to assume that the problem will be electrical? Wire/motors perhaps?

Hope to hear some support feedback
Best regards, stay safe and take care

[William]

Hi,if you find that the Z-axis cannot be moved after assembling the printer, you can refer to this content.

I suggest you remove the threaded rod and move the Z-axis from the LCD.
If one motor is stuck, you can swap the two Z-axis motor cable connectors on the motherboard to check whether the problem will change from one motor to another.
If the two motors are stuck, it is recommended that you replace the Z-axis drive with a drive with good performance.
If both motors work properly, then I will provide you with some tips.
you can refer to this:http://geeetech.com/forum/viewtopic.php?f=82&t=60931
Hope to help you.