17 Jun
2012
17 Jun
'12
8:34 p.m.
I have an old project laying around that I just spent another two hours
on ..
It is an 1993 external parallel port attached CD-ROM. A company called
"Storage Devices Inc" made it, and IBM resold it. The model number is
SCD-683. There are some traces of it if you search the web, but not
much interesting. I have the drivers so that is not a problem.
The CD-ROM is a 1x SCSI unit that uses a caddy. There is a parallel to
SCSI bridge board in the enclosure based on the NCR 53C80 chipset, which
was well known back then. The CD-ROM does show up and talk when used on
an XT running PC DOS 3.3; it responds to commands like eject and it lets
me see its error counts using a utility program.
The problem is that it refuses to read any media that I give it. The
drive is very clean - I removed the top and had a look inside the
mechanism to be certain. It is a caddy loading model so I can't tell for
sure that the head has clear access but everything seems to be operating
freely. I'm using old pressed aluminum discs (OS/2 Warp) which should be
fine in any CD-ROM device. I have tried cleaning the heads with a
special CD that has the magic fibers on it, but nothing is helping. (I
even reached in gently with a Q-tip and isopropyl alcohol, but that did
not change anything.)
Most older (at least) CD-ROM drives and CD players do muc hthe same thing
when asked toread a disk. They go through this sequence :
1) Turn on laser, get intensity correct
2) Energize focus coil, move objective lense away from disk until focus
point found (they normally do this a couple of times)
3) Start spindle motor,start to track, get speed correct.
So, you want to see how far into that sequence it's getting. In
particular, is the disk ever spinning when toy try to read it? If not,
it's either that the spidnel motor or its drive is defective _OR_ that
the thin never foudn the focus point, possibly due to problems with the
laser.
If the disk is spinning, there will be a testpoint on the photodiode
preamplifier where you cna conenct a 'scope to see the 'RF Eye' pattern.
Thsi point is often lavelled, amazingly, and conencting a 'scope there is
a good next step.
-tony