I know, I'm a guy, so what would I know about a sewing machine...
You might be surprised ;)
But jokes aside, every once in a while for the experienced operator and much sooner for the beginner you can have an accident.
By accident I don't mean the usual, a broken needle or some yarn messed up around the mechanics surrounding the bobbin.
Forget my ignorance but I have no clue how the hook thingy is called that holds the bobbin in the machine LOL
I am talking about the real crash: The needle hit the rotating hook with enough force so that now nothing works anymore.
For a lot of people this is now either a bin job or might encounter a more or less expensive service bill for the machine.
I learnt the stuff from my great-grandmother on a (now called anitque) Singer treadle machine.
They were virtually indestructable, unlike modern electric machines on the home level.
But they needed more attention and service by the owner, so once a year I helped taking the machine apart for a decent clean follwed by the complete calibration of the moving parts.
The proper working during a stitch rely mostly on the timing between needle and hook, the rest is adjustments for the thread tension and so on.
What happens during such a violent crash, did I damage something and can I really fix it?
Last things first: Yes, in 99% of cases you can fix it fast and easy yourself!
Ok, you got a big bang, maybe the needle was broken too but after replacing it you realise it no longer moves all the way down - it hits something!
In most cases this happens with thick materials or while the operator was forcing the material through the machine.
Never pull or push the material as it will bend the needle, causing a crash!
Of course in rare cases it can happen that the needle now won't go down all the way - but I address at the end as it is far less common.
This is how it looked before the crash:
And here you can see that after breaking the needle it now get's stuck.
For you it might be that the needle is hitting the outer rim somewhere or that it is stuck in a different place.
In this pic you can see one of the three screws holding the hook mechanism on the spinning axle:
Loosen these screws but only only so that they still hold all in place.
When you can moove the mechanism with sligh pressure it is good.
As you could already see in the first video the needle needs to be in front of the hook on the way up.
Here is the basic alignment procedure:
Make sure the machine is set to a straight stitch with the needle centered, so no fancy patterns or the needle moved to either side.
Remove the foot and the plate - the plate should just pop out with a bit of pressure from underneath.
Turn the machine by hand while adjusting the hook wheel to avoid a crash - I prefer to just hold it in place so the hook is already in the right spot.
Now, when the needle moved about 2mm up again, the point of the hook should be right behind the needle.
Fasten one or two of screws slightly to move on to the final adjustment:
Set the needle postion to the left and check if the needle already moved up when the hook point is behind it, do the same for right side.
If either side is far different adjust the hook wheel to even it out - you want the same relation of needle height and hook position for left, middle and center.
Once satisfied make a few turns by hand to confirm the needle is not hitting or rubbing against other parts of the hook wheel.
In some cases you have about 2.5mm of play, back to front, for the hook wheel position.
You have to make sure the needle runs free between the parts of the hook wheel, if not adjust this "gap".
When all is done comes the final test on an old rug with the widest zick-zack stitch:
As you can see in the above video it all works fine again, the entire procedure (once you have done it a few times) should not take much more than 5 minutes.
There is however the rare case that the rod holding the needle has moved.
It is adjustable too but usally factory set and secured with several screws.
When you open the flap for the lamp you see the mechanics.
As this bit is quite different from model to model I did not take a pic here.
You can identify a crash on this rod quite easy as the needle no longer moves all the way down.
I only had this happen once and that was with thick leather and a really thick needle, during normal use a crash always destroays the needle, rarely cause the hook wheel to out of alignmet but almost never this rod fails.
To set it right you can be lucky and see clear indications of the original position.
If that is not the case follow the above procedure of alignment but when the needle is at the lowest point you adjust the rod height.
The needle must not hit too far down to touch the hook wheel, just so that the hole for the thread moves about 3-5mm below the hook point.
As said: all machines are different and if doubt find the original specs for your machine through Google.
It will require a bit more checking and testing to get it right if the hook wheel was whacked out too so take your time and once the basic alignment is done do some checks with the widest zick-zack.