further research has revield, that if I manually turn the tonearm towardss the center, (thaht is I push the tonearm all the way to the left, so it touches the other arm) the whole carriage is mooving too :-) Whitch must mean, that the motor gets its signal too late - now I only need to know how to adjust it.  :-)

anyone???

A small adjustment of the "second" arm, towards center, did the trick - its not 100% parralel to the tonearm anymore, but its hardly visible, and the unit is playing as expected - thanks for all the input.

They will only be parallel at rest as the tonearm is offset to the left during playing anyway.  Glad it's sorted.  Well done.

Dave.

Adjusting the opto would have been the right way.
The LDR is obviously getting weak and it will only become worse.
When you replace the LDR you will have to adjust the opto - now after having adjusted the sensorarm first.

Martin

Dear Citronix, I have exactly the same problem with yours; Could you kindly send me the picture about the "second arm" mentioned in your solution? You can send me the email to danielshenmail@163.com; I desperately need such solution. Many thanks!