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On Feb 8, 8:55 pm, "Arfa Daily" wrote:
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On Feb 8, 7:26 pm, "Arfa Daily" wrote:
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On Feb 8, 11:49 am, "Arfa Daily" wrote:

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My Sega CD, which uses the KSS-240a laser assembly, makes a spine
chilling sound when it gets warm.. I believe it to be a cogwheel
is
expanding when it warms up..

http://www.youtube.com/watch?v=U55FF7NLgn4

Any ideas on how to actually fix this? The system gets no hotter
than
it normally does...

I think that it is highly unlikely that anything is happening to the
size
of
any gear wheels. The (very brief) sound that can be heard on your
clip,
sounds like the motor pinion slipping against the intermediate drive
gear.
On a typical mech that uses any of the KSS series lasers, the most
common
cause of this is bad contacts on the laser 'home' switch, normally
located
on the spindle / sled motor connection board, right underneath the
turntable. When the contacts don't make very well, the laser homes
as
normal, but no signal is generated when it gets there, to tell the
system
control micro to shut off the drive to the motor, so it keeps
running,
and
the gears slip against one another. After a while, the vibration
caused
by
this often gets the switch contacts to make again briefly, which
then
causes
the drive to be cut. My first move would be to clean the switch.

Arfa
An update: I watched the laser move, and when it screeches, it's not
even near the home switch.. The motor spins, and the cogwheel does
move, but misses on the other gear (it never slips on the sled)...
There's a decent amount of play, because if I manually turn the
cogwheel, it does sometime miss too..

Thinking about it, there was an issue with some Sony decks (which this
almost certainly is) with two of the gears being right at either end
of
their size tolerance specifications, and there was a mod kit for it
with
two
new gears. There was a service bulletin about it, as I recall, but I
wouldn't know where to lay hands on it now. If you have a local hifi
repair
shop, they will have scrap Sony decks coming out of their ears, as
many
warranty replacement lasers were supplied by Sony as whole KSM series
decks.
You should be able to get a scrap deck from them, which may not be
exactly
the same, but in general, the gears in the sled drive train are, so
you
can
rob and transplant them into your deck. The other alternative is a bit
of
a
'bodge'. You can slacken the screws which secure the sled motor, then
push a
thin sliver of plastic sheet under the side of the motor closest to
the
intermediate gear. When you tighten the screws back up, the motor will
have
a very slight 'tilt' towards the intermediate gear, which will improve
the
meshing. Not ideal, but I have done similar things in the past, when
parts
have not been available, or have been prohibitively expensive.

Arfa

I will check at a local repair center and see if they have one..

Btw, I took the "drive" out, and noticed the home switch did have a
cold solder joint, i fixed it, but no change..

http://img.photobucket.com/albums/v3...gon/cdmech.jpg
http://img.photobucket.com/albums/v3...ragon/cold.jpg

I have an old Sony, and peeking in, it has a KSS 210B drive. Can that
work? Or is it not compatible?

The '210 laser is completely incompatible with the '240 - different
connectors for one thing. For sure, the 240 will fit on the 210 deck -
the
body shape of both lasers is the same. However, the decks themselves are
quite likely to be different. They may have the mounting rubbers in
slightly
different places, or the actual shape of the metal deck may be subtly
different, for instance. They may have different shaft lengths on the
spindle motor, and differently designed turntables, which have to match
the
disc clamp. There are a number of variations of these decks, many of
which
look the same at a first glance, but are different when you dig in a bit
deeper. However, most of then share the same drive chain gears for the
sled,
so you may be able to cull parts that will do the job, off that '210 deck
that you have found.

Arfa

Ok.

The Sega CD's desk doesn't have any rubber at all, it's hinged at the
back, and at the front, as a piece that attaches to a gear that's run
on the tray, so when the tray closes, the desk pops up into position.
The spot where rubber pieces go at the 4 corners, is actually some
brass colored bolt, which is secured to a fairly large PCB at the
bottom.. The only cable going to the Sega CD's motherboard, is a big
flat ribbon on the right side of the PCB on the deck.


The actual metal deck likely still has the corner rubbers, as these form the
primary shock-resistant suspension system for it. The hinged plastic tray
that is worked from the lifter gear driven off the drawer gears, is just a
carrier for the deck. It is a common arrangement. It is also common for the
rubbers to collapse over time, which can lead to a very tap-sensitive
system, which might lead you to suspect a bad laser. The laser itself will
connect to that sub pcb on the '210 deck'd machine that you have found. The
connections to a '210 are two multi-pin sockets with conventional wires. The
'240 has a single narrow-ish white ribbon.


I will check all my old CD-players for gears that fit.

Btw, side question: I noticed when the 240a is reading a music CD, it
is 1x as it should be.. But when it reads data, it does spin the CD
faster, but not quite 2x.. Sega claims it's 1x read only, and from
what I see, the 240a is 1x only. So why does it spin faster for data?

I've no idea, really. I have seen 'conventional' audio lasers such as the
KSS series, being run at higher than x1 in 'specialist' audio applications,
so it seems that they are capable of it. The decks in personal CD players
often run the disc at x2 or more in an effort to keep the bit bucket full
for anti-shock purposes, but since the Sega is not subject to physical shock
(!) that's obviously not the reason. Might be something to do with keeping a
larger buffer of data available though, due to processing speed or something
?

Arfa