Very weird Behaviour of a Laser Unit´s Connector Cord

[Salar]

Hello,
a VERY strange effect:
When I put my hand very close to a connector cord of my Nakamichi OMS-5AII/EII, I will hear scratches in the music and the laser will even loose track.
I mean n o t touching, just h o l d i n g my finger very close to the connector cord will make the laser loose track!!!

This 8-pin cord (JU101 in the service manual) connects the photo diodes of the laser (KSS-123A) with the R-F Amp (CX20109).
Touching a second connector chord (also 8 pins) which feeds the laser and coils
has no influence at all, as one should expect.
It is just the signals from the laser to the RF-Amp, which can be disturbed as I described.

What I did so far:
I replaced the connector cord, but this had no effect.
Then I wrapped the connector cord with copper wire and grounded the wire , but this this also detoriates the signal.
I then checked the pcb for defective solder joints and loose connections but found nothing.
Checked the ground connections, everything is fine
Finally replaced the laser unit some minutes ago, but also no change.

Any ideas?
All the best, Salar

 

[dnsey]

This is quite normal - you are inducing spurious signals into the RF amp via the cable.

Why worry about it? You don't usually have your finger near the cord when listening to music

 

[Salar]

Well - the top cover will be almost as close as my finger, when the nak is assembled...
What could I do to minimizie this effect?
It is technology fron the mid eighties, could I change the cable to a more suitable one ? I.e those used for SCSI/Ata connectors etc.?
Or, this is diy-audio, even place the RF-amp closer to the laser unit?

All the best, Salar

 

[kevinkr]

Presumably the top cover is steel? A metal cover will provide all of the electro-static shielding required and is an integral part of the design.

I wouldn't get too hog wild with experimenting with the rf amplifier, laser diode, or photo-diode array - you could end up with an expensive mess or your hands or if you really unlucky yet another item to add the endless electronic trash stream heading to your local landfill.

Lots of other areas like the audio circuitry, etc., to play with, and hopefully at less risk.

Of course YMMV..

 

[Mooly]

As dnsey say,s it's normal, all players with a "remote" R.F. preamp exhibit this effect to some degree. As to whether it's good design, well that's another question altogether. Thats one of the reasons why I like the CDM12.4 , the R.F. amp is onboard the pickup. Forget it, don't worry.
Regards Karl