View Single Post
  #8   Report Post  
Posted to sci.electronics.repair
Arfa Daily Arfa Daily is offline
external usenet poster
 
Posts: 6,772
Default Pioneer PDM450 laser help


"David Farber" wrote in message
. ..
Gary L. Woodruff wrote:
howdy, I have a pioneer PD-M450 Cd player that would not play disks.
It would load them but and the laser would go in try to focus but the
disk would never spin. I found the plastic lens had fallen out of the
optical assembly and would not stay in when replaced. I ordered a new
optical pickup and replaced the old one. I have the same problem. I
have confirmed that the spindle motor will run with 1.0 vdc supplied.
I do not see any voltage appear at the motor leads while the lens is
trying to focus. Please help, optical pickup was $$$$.

thanks, Gary


The replacement pickup may not work right out of the box because IIRC, it
doesn't come pre-aligned. You'll need to boot it into test mode and use a
scope probe to adjust it. I believe it's called the gradient adjustment.
Might just be easier to do as the previous responders have suggested which
is to carefully glue the lens back on. Make sure whatever glue you use,
that it doesn't fog up the lens!

--
David Farber
David Farber's Service Center
L.A., CA



Yep, 100%. Aligning these pickups is a mother of a job that requires a
special small disc to allow access to the diffraction grating adjustment
screw in the top of the laser. The delicacy of this adjustment, and the
ridiculous level of accuracy required, makes me defy anyone to get this
adjustment exactly 'right', without factory conditions, and a high skill
level of working with CD players. Note also what someone else said about
the laser diode shorting points. They are on the orange flexiprint
connection tail, by the tiny laser power set pot. They come with a blob of
solder across them.

The 'fallen out lens syndrome' is very common, and is always repairable.
The trick to getting it to always work out ok, is to first spend some time
with a sharp and tiny-bladed modeller's scalpel, removing *every trace* of
the original glue from *both* the lens seat, and the rim of the lens
itself. The lens can then be refitted, and held square in the carrier with
tweezers exerting slight pressure on opposite sides. Rapid cure two part
epoxy that you've already mixed, can then be applied to four spots around
the lens edge, using the tip of a darning needle.

After the glue has thoroughly set, any slight optical misalignment can be
easily taken out using the raft of controls available on Pioneers
(tracking offset / balance / gain, focus offset / balance / gain). All of
these can be set easily using a 'scope to observe the eye pattern at TP1.

Sorry to be negative about your new and expensive pickup, but honestly,
you *will* struggle to ever get it going. Just as a further slight downer,
these pickups must be amongst the most reliable ever made and used by any
manufacturer. Since CD players first appeared in the 80s, I would say that
I have replaced no more than five of these, that were genuinely faulty.
The other very common problem on these players, that inexperienced people
often mis-diagnosed as a bad laser, was a defective spindle motor.
Sometimes, a bad motor would try to rotate the disc, and squeal horribly
in the attempt ...

Arfa