I don't think the detector arm is the issue. I don't think this machine has the ability to detect tracks. I believe the raising and lowering of the arm and "Q"ing is done with the buttons.
The next step it to search where the signal to the arm solenoid fails. If you friend has a DVM or oscilloscope and can follow a schematic I may be able to talk him through the troubleshooting.
If this does not happen and you don't find a way to get this machine working at a cost which is reasonable with its value, I have been lusting after a Beogram 4002 since they came out. If it is complete I will consider a swap for a working Beogram 3000 which is contemporary with your machine. I'm lacking the dust cover for the machine in question, but I keep looking on eBay for one. The 3000 has a pivoted arm and to my knowledge is the last to use the SP type cartridge which have replaceable styli.
Stevelocks3 wrote:Phil, thanks for the reply and your continued interest. Sadly I have no useful equipment, only some old meters which are unfamiliar and may be unreliable, but my new friend has some gear, although he prefers valves and older mechanical items, though he is willing to Help me. I will ask what he owns. To remind you; the arm worked well at first some months ago, but now will only move over the disc to the centre and return to rest when the "play" pad is pressed. It can be halted partway and moved both ways but will not lower, so it is getting lateral signals but not verticals. Could the "detector" arm be at fault?