Magnavox/Collaro changer problem

Hi, I have a 1956 magnavox phono with the collaro changer.
Everything works fine with the playing and the changer cycle works perfect except for a tiny problem.
It's just when I play 12" ( 33 1/3) records. The tone arm rises, the record drops, the tone arm moves toward the start of the record, the arm lowers onto the record, then the changer gives off a click noise or cycle lock noise, but the tone arm jerks a little forward when this click happens. It scratches the first 2 or 3 threads of the record.
I tried the cycle with 7" and 10" records but everything goes smoothly like it should. Is there an adjustment on the bottom to stop this tone arm jerk?

Is this the 3-size Continental changer with the dropping record feeler, or the Conquest changer that uses the pickup arm to measure the records?

One problem is the groove guard they put on 12" records made after 1966, when they started making records thinner. it is sloped, and the arm will slide down the slope and bounce across the grooves. The stylus force is the cause, and the stylus starts to slide the moment the mechanism releases the arm. Newer changers use a bit of temporary friction to eliminate this, or have a slightly different index position for 12" to set the arm inside the groove guard.

This changer does have the record drop finger to determine the size.
I am guessing RC 54 or RC 456.
The tone arm has an Magnavox head shell mounted on it.
I even cycled the changer without a record and let the arm come down in my hand and when the arm rested, the changer clicked and I can feel the arm lurch a little forward.

Hi,
Seen your post over on Magnavox Friends. See you got the "man" interested and that's good. I was just going to say redo the set down on the the 10" record so it will start in the first groove and try again.
Bill

Hi Bill, Thanks for replying,
I tried adjusting the arm to go to the very start of the record but all that would do is jerk the arm more until it skipped a couple of threads.
I even tried to adjust so the needle comes down on the actual playing threads and it still skipped a couple of threads when the changer makes that clunk sound after the arm sets down.

Also, this only has this problem with the 12" ( 33 1/3) records.

Hi,
Excuse me because I'm an old man and don't quite understand your reply. You do know the set-down adjustment is made with a 10" record? These changers are reasonably accurate in that regard. Turn the adjustment so the needle sets down in the first groove of the 10" record. Then it should set down for all sizes. If this does not correct it work your overarm back and forth and up and down. This should move freely. I hate to work on changers. You got guts to dis-assemble one. Too many parts and small springs can get "re-shaped" and no longer have proper tension. Most changers just need a good careful cleaning and relube...my opinion there.
Bill

I thought of two possibilities:

1. Is something pulling the tonearm wires? Check how the leads are dressed.

2. Is the arm raising height misadjusted. It might be that the arm clutch is disengaging too late. The lower adjustment affects when the clutch disengages, the upper one does not.

I did the grab the arm trick also and found that the arm actually did jerk a little.
I did indeed found the cure.
Underneath the changer is a small nut adjustment that puts a little friction to the arm to reduce erratic movements. If you go too far, the arm stiffens too much and the needle will skip on the record. You have to have it just right. I want to thank everyone on here that had their thinking caps on for this one. Gary.