T-Gain in cd player
 

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Hello all,

I recently got a Kenwood RXD-25L, which is an integrated stereo system
with cd, cassette, tuner, eq and stuff.

The cd player didn't recognize any disc. The whole box was very dusty
inside, so I tried cleaning the lens. The player came to life, but it
had seek problems. On some discs it wouldn't play at all, some others
just made it seek a really long time. I played around with the
adjustments, and turning one marked "T-GAIN" got the player working.
Sounds like Tracking Gain, or something like that? I just cranked it
almost all the way clockwise, and now every disc I tried plays just
fine.

What exactly does this adjustment do? I'm guessing it doesn't alter the
laser power, since I noticed a trimmer near the pickup. (Didn't touch
that one.) Should I expect problems in the future?

br, Ilkka


T Gain is indeed tracking gain, and it adjusts the gain of the amplifier in
the tracking servo loop. Likewise, F Gain does the same for the focus servo
loop. Adjusting either of these up has no significant detrimental effect on
the player, other than to increase the servo noise. This is the
' whistly ' noise that you hear goming from the laser head - particularly on
discs which are in less than perfect condition, and is the result of the
lens vibrating on the focus and tracking motors ( much like a tiny
loudspeaker, and turning up the servo gains is like turning up the volume ).

The pot on the laser should not be touched ever, unless it's one of the
players where this is an official adjustment, such as Pioneers. Do not touch
tracking balance ( E-F balance ) or focus balance, or PLL, unless you know
what you are doing.

I don't think, from experience, that your " fix " will last long. Usually,
if a clean doesn't do the job on its own, it indicates that the laser output
power is already low or, more likely if the player was very dusty, that the
laser's internal optics ( the critical angle mirror ) and the pickup chip's
optical face, are dusty also.

If you do replace the laser eventually, don't forget to return the pots that
you have adjusted, back where they were ( mark them now as you will have
forgotten where they were in a couple of months ... ) Generally, the
manufacturing tolerances of replacement lasers are very good, and a new one
can be dropped into a CD player without need for circuitry adjustment - and
before everyone starts screaming that you should always adjust them, yes I
agree that they should be checked and adjusted as required if you're doing a
professional job, but it's normally fine to leave them alone if you're an
amateur. The same does not apply to DVD lasers, however, and these will
almost always need adjustment, which is why many of them come as complete
deck assemblies.

Arfa