P90 full auto lock?
 

Yeah so my KA p90 has gone from being able to shoot in semi to full auto only. Im not sure where to start, any insight is welcome.

There are a few possibilities, with the first being arcing between your trigger contacts. Your p90 should be a 2 stage trigger when set to full auto, with a partial squeeze being semi and full squeeze pushing full auto. The most common issue is arcing between the contacts and all that would require is a cleaning of the contacts themselves. Another possibility is the contacts being separated too much which can be finicky to reset them back to normal. If your p90 is in fact set up on a micro switch, it's possible the spring for resetting the switch is faulty. My best recommendation overall would actually be swapping the innards for a complete hpa build. Makes things a bit easier in terms of tech work.

Check your cutoff lever. It's not uncommon for them to wear out, prometheus makes a replacement that is hardened steel.

Check the precocking spring also I had this happen to me with mine and found that the 1 post on the outside of the Gearbox for the trigger contacts had broken. It could also be your tappet plate as those are finicky on the P90's

From what I have researched I would agree with everyone's troubleshoot but I would start with the cutoff lever. Check my previous posts on how to reinforce a KA P90 and a mag feed fix that gave me positive results. Cheers