Packard MP3 not working correctly

So you have measured the resistance at each selection and it changes .2-.3 volts progressively?

Also, the coin micro switch on these can be problematic, have you tried bypassing the switch?

Or testing the voltage output at the switch to ensure it also shows the progression of the .2-.3 volts for each selection.

You can try wiring in a momentary switch to replicate the signal from the coin switch, they can provide a more consistent contact to allow the proper voltage to pass.

When you say you used another wallbox – you have two and they produce exactly the same result?

I can’t edit my first post but pictures of your wiring and switch mechanism would help there are a few different versions of this wallbox.

Can’t really help you if you won’t communicate.  There is generally no easy solution if you have followed the Retroelonik instructions correctly, but you have not made that clear.  From your description I would guess that there is an incorrect voltage pulse from contact one to contact eight and 23 to 24. If you can provide those voltage readings, and they are correct then you may have a bad PCB and the folks at WB2MP3 will send you a new one as they have done for me in the past.  The easiest way to do that is to put your test leads at the signal and negative posts on the PCB and record the voltage at each selection, if they start at about .2 volts and progress at .2 to .3 volts at each selection and don’t provide the right song you may have a bad board.  I’ve done a couple of these and found the most probable point of failure is the coin micro-switch, it often does not provide enough contact to signal the right voltage reading to the PCB.  One solution might be to install a momentary switch to provide enough contact interval to let the voltage pulse to pass to the PCB .  Hope you get it worked out.

@ Gemmy – Did you ever solve this problem as I have exactly the same issue with my unit ?