I am sorry my description has thrown you off, perhaps it would be more accurate to say "the result of inserting the cassette- is that the cassette door continually opens, or will not remain shut -without any mechanism activating".
In answer to your question -
"So, the mechanism 'thinks' that the tape has not fully loaded, and is trying to eject it again by opening the door, but it does not actually eject, correct?" Partly correct-
I don't know what the mechanism "thinks", but all I can say is that the result of inserting the cassette is that the door immediately opens when my finger pressure is released from the door.
The exception to this however is- if I insert the cassette during or after the first whirring sound & before the second whirring sound the cassette door remains shut for about 2 seconds-it then ejects the cassette- this is the only time the eject mechanism works.( I assume the 2nd whirring sound is the eject mechanism activating)
During this time the two pins that slide & carry the tape onto the play head do not move. I am assuming this is what you call "load"- so the tape is not loading.
I appreciate your point " a trained technician can view the mechanism operating and decide which part needs adjusting - this will be difficult for you if you are not used to observing and tweaking the eject mechanism in a VCR".
This is why I am paying for expert advice-if you feel you are unable to help me find a solution just let me know.
Unfortunately I do not have a similar product to compare mechanisms.
What do all these clues mean? & How can the solution be found?