LaserDisc Database
https://forum.lddb.com/

RF Level - what does it actually do??
https://forum.lddb.com/viewtopic.php?f=30&t=8188		 Page 1 of 1
Author:  audioboyz1973 [ 28 Dec 2018, 09:55 ]
Post subject:  RF Level - what does it actually do??
So I've been going cross-eyed staring at the circuit diagram of the laser pickup (p15 of the X9 service manual) and where it connects into the MOTHER ASSY (p60).

Does adjusting the RF level pot actually 'turn up' the laser output or is it just controlling the level of amplification applied to the RF signal from the laser before it heads into the RF Buffer circuit?

My understanding of electronics is pretty rudimentary but I think the latter? (The circuits that drive the actual diode seem far removed from the RF Level section but like I said my knowledge is very low and maybe there's some feedback loop there I don't understand.)

What I'm trying to work out is turning up the RF level on a weakening laser just boosting the incoming RF signal (which is desirable) or is it actually driving the laser harder; which would probably only hasten its demise and not be good.
Author:  kencol [ 30 Dec 2018, 21:34 ]
Post subject:  Re: RF Level - what does it actually do??
I would also like to know this but think it’s more likely to just apply to the rf level and not the output of the laser
Author:  krbahr [ 31 Dec 2018, 03:17 ]
Post subject:  Re: RF Level - what does it actually do??
Amplifies the signal received from the laser. If you have to turn this up your laser is starting to show it's age.
Author:  audioboyz1973 [ 31 Dec 2018, 04:17 ]
Post subject:  Re: RF Level - what does it actually do??
Thanks Kurtis!

I had an X9 not working properly and based on the symptoms and your advice scattered here and elsewhere over the years narrowed it down to an RF level and/or Focus servo issue. Not wanting to just "fiddle with the pots" over the last few months I've accumulated an oscilloscope, signal generator and even sat down with my phone and google translate app to translate a couple of bits of the service manual!!

Anyway finally found the time to work on it over Christmas/NY break and happy to say now have it working :D
Had to adjust the RF level as well as both the Focus and Tracking gains (which I also assume work as per the RF level adjustment) so seems certain to be a case of the laser weakening over time. All the other adjustments I could measure/check without the muse test discs seemed to be in the ballpark.
Author:  pbiancardi [ 11 Jan 2019, 01:48 ]
Post subject:  Re: RF Level - what does it actually do??
krbahr wrote:
Amplifies the signal received from the laser. If you have to turn this up your laser is starting to show it's age.


It is ok to turn this up and leave that way though? Not going to hurt anything else? I have a Sony that needed a little turning up of RF level, is it ok to run it like that?

Image
Author:  krbahr [ 12 Jan 2019, 04:06 ]
Post subject:  Re: RF Level - what does it actually do??
It does not affect the life of the laser, it only performs a level boost of the signal provided to the electronics from the laser. If you turn it up too high you could add distortion from the amount of signal available or fold over distortion at the top to demodulate the FM signal to the analog composite signal. But if you were just turning it up to the point where it plays without dropouts, that would just be adding a little life for a laser output that is getting weak. Or maybe it was adjusted incorrectly in the first place or by another. You normally put in a properly mastered CD and adjust the RF signal after output by this to 300mV P-P in Pioneer units. It is a level that provides a good sign to demodulate.
Page 1 of 1 All times are UTC [ DST ]
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
http://www.phpbb.com/