I built my 3d printer from a kit a few weeks ago, and initially, it was working fine. However, when I took it with me to college, something must have went awry. The first layer comes out fine, but afterwards, the infill breaks apart. It extrudes the entire time, but there are gaps in it that make prints porous, unisitely, and brittle. The printer is a prussa i3 knockoff. I have included a gallery of a recent print attempt of mine. I hope you guys can help me diagnose the problem.
For your troubleshooting process, I would suggest to use a simple model, perhaps a small cylinder of 20-25 mm diameter, 5-6 mm height.
You've not indicated what material you are using, nor the extruder/nozzle temperatures, but the print appears to be suffering from low temperature problems. You would also include the slicer software name although I don't believe this matters.
The initial layer will print reasonably well, if your slicer performs a reduced speed layer one. The slower filament movement through the nozzle allows it time to heat up for an acceptable layer, while the faster later layers will prevent enough heat to be imparted to the filament.
Increase your temperature at least 10°C for the initial test, as your part is quite a bit below temperature, in my opinion. If the first test is not acceptable, increase by 5°C for each succeeding test.
Keep in mind that individual brands will have different optimum temperatures and within a specific brand, different colors will require temperature adjustment.
The "initially working fine" reference does not include information regarding filament change, color change or other useful information such as print speed, layer thickness, etc., but I'm aiming for a temperature adjustment as the most likely answer.