16 Sep
2012
16 Sep
'12
3:54 p.m.
I have powered up the LA36 with the Selenar Graphics board in it, and
from the information kindly obtained by list members
(Byte Magazine
article about the Selenar Graphics II), I have been able to verify
that
the unit indeed works. The graphics mode works, and all of the other
features documented in the Byte article seem to function properly.
The issue that I've found is that only 5 of the 7 print pins are
working. Numbered with the top pin as number 1, it is the 3rd and 6th
pins that are either not firing at all, or are jammed such that they
can't come forward enough to make an impression.
I can't find a service manual for this unit online anywhere, so I'm
wondering what the best approach to diagnosis would be. I do have
schematics, but since the unit has a Selenar Graphics II logic board,
I'm not sure how well the schematics will help. Since the Selenar board
replaces the stock logic board, I can safely assume that it retains the
pinouts for the connectors that go from it to the power board that has
the drivers for the solenoids in the printhead. So, I can probably
scope out the drivers to see if they are firing on pin 3 and 6 when
printing characters that require those dots, which I will do when I have
time, but I'm wondering the next step would be if I find that there are
firing pulses coming out of the pin drivers for pin 3 and pin 6.
Obviously, if I find that the pulses aren't being generated, then I have
to dig into the solenoid drivers for these pins and figure out what has
failed and fix it.
If I find that the solenoid drivers are OK, then what should be done
next?
Would it be to remove the printhead and do what Tony suggested, which
would be to use a bench power supply (I have a good Tektronix bench
supply does truly does deliver 0.00V) to try to fire the solenoids to
see if they are gummed up? If so, how do I go about removing the
printhead to do this? Just from looking at things, it looks like I would
have to do a lot of disassembly to get the printhead out of there. Does
the printhead come off separately from the carriage that it rides on, or
do I have to remove the whole carriage assembly?
Any guidance would be most appreciated.
Thanks,
Rick Bensene
17 Sep
17 Sep
12:10 a.m.
--On September 16, 2012 3:54:31 PM -0700 Rick Bensene
<rickb at bensene.com> wrote:
I can't find a service manual for this unit online
anywhere, so I'm
wondering what the best approach to diagnosis would be.
The maintenance manuals for the LA36 used to be on the University of
Queensland Museum of IT web site. This site is now dead, byt the
Wayback Machine still has it. If you look at
<http://web.archive.org/web/20090914043922/http://www.computer.museum.uq.edu.au/documents.html>
you'll see a fairly impressive list of DEC (mostly) manuals. Both
volumes of the LA36 maintenance manual, as well as the illustrated
parts breakdown (and the user manual) are on the list. I didn't try
downloading them but if that doesn't work, I have copies that I saved
back when the site was still live. Too bad they shut it down.
There are also a few things on BitSavers and there is a page listing
LA36 documents at
<http://terminals.classiccmp.org/wiki/index.php/DEC_LA36>, but most of
the links there point to the UQ web site and are dead.
Mike
9:46 a.m.
On Sep 17, 2012, at 3:10 AM, Mike Alexander wrote:
The maintenance manuals for the LA36 used to be on the University of Queensland Museum of
IT web site. This site is now dead, byt the Wayback Machine still has it. If you look at
<http://web.archive.org/web/20090914043922/http://www.computer.museum.uq.edu.au/documents.html>
you'll see a fairly impressive list of DEC (mostly) manuals. Both volumes of the LA36
maintenance manual, as well as the illustrated parts breakdown (and the user manual) are
on the list. I didn't try downloading them but if that doesn't work, I have
copies that I saved back when the site was still live. Too bad they shut it down.
There are also a few things on BitSavers and there is a page listing LA36 documents at
<http://terminals.classiccmp.org/wiki/index.php/DEC_LA36>, but most of the links
there point to the UQ web site and are dead.
It turns out that this archive is also on Bitsavers at
<http://bitsavers.org/www.computer.museum.uq.edu.au/pdf/>.
Mike
18 Sep
18 Sep
10:20 a.m.
I want to express my thanks to the list, especially Mike Alexander, Tony
Duell, Richard (Direct 3D Graphics Pipeline), and Rod Smallwood for
hints about getting the LA36 with the Selanar Graphics controller
working.
The two missing dots on printing were due to failed solenoids in the
printhead. The drivers were doing what they should, but, the solenoids
weren't firing. Checking the resistance of the solenoids showed them to
have much lower resistance than the other solenoids. Fortunately I
have a spare printhead from a scrap Tektronix-badged LA35 (Tek 4641), so
I pulled and tested it, and all seven solenoids fire (thanks, Tony, for
the bench test procedure) properly. I put this printhead in the LA36,
following the printhead replacement procedure in the maintenance manual
(thanks, Mike for the leads on finding scans), so that it was properly
aligned. I double-checked everything and powered it up, and behold --
fully formed characters! The graphics from the Selanar board also look
much better (done by hand-typing in graphics commands with the terminal
in local mode). Thanks to Rod for the pointer to the Byte Magazine
article on the Graphics II board, which had some of the command set in
it.
The next step is figuring out how to talk to this thing through RS-232
serial. The Selanar board has a DB-25F connector on it that I assume
is RS-232. There is also a current loop interface on the board, using
the same pinout as the original DEC controller board. I can tell
because there is a cable that was plugged into this connector that has a
DEC-style mate-n-lock connector on the end for connecting to the current
loop interface on some DEC machine. There are a lot of jumpers on the
Selanar board, and I'm wondering if they configure whether the serial
interface is current loop or RS-232 on the DB-25. Without docs on the
Selanar Graphics II board, knowing how to set them is going to be a
challenge.
I think it's just going to be a matter of scoping out signals and
figuring out which interface is active, then using whichever is. I am
assuming its likely be the current loop because of the cable already
being there. If so, I'll have to build/buy a current loop to RS-232
converter if that is the case, but that isn't that big of a deal.
Still would like to find anyone that might have a manual for the Selanar
Graphics II board for the LA-36.
Rick Bensene
6 Oct
6 Oct
7:29 p.m.
I did some research on google books and identified all the Selanar
products I could find:
<http://terminals.classiccmp.org/wiki/index.php/Category:Selanar>
I also found a manual for the Graphics-100:
<ftp://ftp.informatik.uni-stuttgart.de/pub/cm/vt100/Selanar%20Graphics%20100%20plus.pdf>
--
"The Direct3D Graphics Pipeline" free book
<http://tinyurl.com/d3d-pipeline>
The Computer Graphics Museum <http://computergraphicsmuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>
17 Sep
17 Sep
12:25 p.m.
New subject: University of Queensland scans (was: Selenar Graphics II LA-36)
In article <C1CDDE9A9858C7218C4FBC86 at bayswater.msalexander.com>,
Mike Alexander <mta at umich.edu> writes:
The maintenance manuals for the LA36 used to be on the
University of
Queensland Museum of IT web site. This site is now dead, byt the
Wayback Machine still has it. If you look at
<http://web.archive.org/web/20090914043922/http://www.computer.museum.uq.edu.
au/documents.html>
Bitsavers has a mirror:
<http://bitsavers.org/www.computer.museum.uq.edu.au/>
--
"The Direct3D Graphics Pipeline" free book
<http://tinyurl.com/d3d-pipeline>
The Computer Graphics Museum <http://computergraphicsmuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>
12:58 p.m.
I have powered up the LA36 with the Selenar Graphics board in it, and
from the information kindly obtained by list members (Byte Magazine
article about the Selenar Graphics II), I have been able to verify that
the unit indeed works. The graphics mode works, and all of the other
features documented in the Byte article seem to function properly.
The issue that I've found is that only 5 of the 7 print pins are
working. Numbered with the top pin as number 1, it is the 3rd and 6th
pins that are either not firing at all, or are jammed such that they
can't come forward enough to make an impression.
I assume this is nthe standard LA36 pinthead.
The first thing to do is to remvoe it can clean the business end with
propan-2-ol. Take care not to use toomuch, you cna disolve the adhesive
that holds the synthetic gemstone bearing in place.
Now, fro mteh DEC printset, check the resistance from each of the drive
connections to the common conenction. They should all be much the same.
If pins 3 and 6 test open then either the coils are burnt out (==new
printheat time) or more likely the flexiprint conenctiong to the head is
broekn. Often this can be carefully repaired.
Then use a bench supply, one side to the common conention, otehr side ot
the pin 1 derve. Turn up the votls and wath the pin. See what sort of
votlage makes the pin extend, and how far out it comes. Repeat for the
other pins, Do pins 3 and 6 behave i nthe same way?
If hte head is OK, next step would be the driver s o nthe power supply
obard (IIRC). I doubt the problem is further back i nthe logic, fortunately.
-tony
4093
days inactive
4479
days old
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