31 Mar
2010
31 Mar
'10
2:24 p.m.
On Wednesday (03/31/2010 at 07:26PM +0100), Tony Duell wrote:
Indeed. I was a little worried about depending on that jumper (and the
associated connector pins) to ensure that the zener clamp would stay in
place else fry my microcontroller. So, I put a front-end on the micro
using 26LS32 line receivers and accept the 12V levels directly or any
level above about a volt I guess.
If you get
stuck, I can sure help. I recently restored an HP 2748B
optical reader (500 CPS) and built an RS232 interface for it so that
I restored one of thoise a couple of years back -- or actually the -A
version which has simpler electronics (but much the same functionality).
I got the HP9800 interface for it (HP11202 Opt A01 IIRC) on E-bay. As you
probably know the outputs of the 2748 are pilled up to 12V, but through
10k resisotrs, whcih means they will feed the 180R/390R-terminated TTL
inputs of the 11202 with no prolems. Of course the -B model that you have
has clamp diodes anyway so you can force the outputs to TTL levels by
jumpering 2 pins on the connector. What was wrong with yous? Mine had a bad mbearing in
the magnetic clutch.
T oreplace that I had to make special tools to press the clutch unit
aprt and put it togetehr again. The ball race itself was a standard size
and I had no problems getting one. Of course I also had to make the
alignment mandrel to ge the clutch parts centred up wehn I put the motor
unit back on.
Wow. I was much more lucky. Mine had numerous burned out blubs in the
illumination head and a bad transistor on one of the detector channels.
And it was pretty dirty inside. But, mechanically, I think I lucked out.
There are a few photos in my flickr account
(tony_duell) of the internals
of the read head and of taking the motor/clutch apart.
Cool. I'll check it out.
Mine works real nice for reading these old tapes. I posted a thing to
this list a year ago or so... that the problem I have with the tapes
is that they were stored for years and years with a rubber band around
each one... the oil on the tapes eventually dissolved those rubber bands
into very sticky, gooey messes that have soaked into many of the tapes.
At the very least they are stained with the blue, green, red, pink or
whatever color rubber band used to be around them and at the worst,
the goo is glueing the tape together and will take careful attention to
unstick without tearing the tape.
I even have one of M$ Gates original 4K BASIC for the Altair 680 still in
unopened, original packaging. Unfortunately, this too had a rubber band
around it and there's a big puddle of goo in the bag along with the tape.
Sigh.
--
Chris Elmquist