19 Jun
2014
19 Jun
'14
11:55 a.m.
The other night I picked up a TRS-80 model II from a seller on Craigslist. The computer
had apparently belonged to an account and it came with lots of binders of TRS-80
accounting software manuals and boxes of disks filled with old client information.
It came with some no-name 3rd party external dual 8" drive and a gigantic Centronics
703(?) printer. I tested out the computer when I got home and it looks like it probably
works fine, I was able to power it up without any smoke coming out and get it to boot into
one of the CP/M disks I found in the box. The keyboard is another matter, but I've
already been pointed to a few sites that discuss how to deal with the foam pads inside the
capacitive keyboard.
I didn't get a cable for either the printer or the external disks, although I'm
not really worried about hooking up to the parallel port since I doubt I'm really
going to want to print from the TRS-80 anyway. I did open up the external drive case and
it has two genuine Shugart drives in it, and I've already ordered some 50 pin IDC
connectors so I can make up a cable to connect it to the TRS-80.
I'm having a heck of a time hunting down a manual for the printer though. I *think*
it's a Centronics 703, but the 703 was blacked out on the nameplate on the back, and
there's no identification on the front. I definitely need to get a new ribbon for it,
but it looks like instead of replacing the ribbon as a cartridge, you pull the whole
ribbon out of the screwed in case and then have to pack a new one in. The pinch rollers
for feeding the ribbon are pretty old and now flat on one side, but after a touch of oil
they do *seem* to be turning and feeding the ribbon.
I've posted an album up on Google+ of the computer, you can see it here:
https://plus.google.com/112185595588625076298/posts/KT4mtRJtCAs
20 Jun
20 Jun
2:23 p.m.
[TRS-80 M2 and printer]
I didn't get a cable for either the printer or the
external disks,
I seem to remember that early versions of the disk controlelr PCB i nthe
M2 has the internal and sxternal drives o nthe same bus. This had the
undesirable feature that if there was nothign conencted to the external
drive conenctor (no expansion drive unit or terminator), there was no
termination (and thus no pull-ups) on the intenral drive signals either.
The general result was a corrupted disk. Sounds like you hve the later PCB.
The priner cable is straight through from an IDC socket to a microribbon
plug. If you want one it's easy to make.
I'm having a heck of a time hunting down a manual
for the printer
though. I *think* it's a Centronics 703, but the 703 was blacked out on
the nameplate on the back, and there's no identification on the front. I
Ah... It probably is a Centroics 703. Is it the right colour ir is it
'battleship grey' like the computer? IIRC the rist Radio Shack 'Line
Printer' (which was not a ture line pritner, of course) was actually a
Centroics 703 with grey case mouldigns. No internal changes at all.
If this is the printer I am thinking of (and from your description of the
ribbon I think it is), the carriage motor is an AC shaded pole thign that
runs all the time. It drives a belt acorss the printer. Solenoids in the
carriage grab the top or bottom run fo the belt to move the carriage. Odd..
Anyway, I managed to get the service manual for the Radio Shack Line
Printer (the user manual mayeb there too, but I didn't need it) from
http://www.archive.org/ It might be worth a look.
definitely need to get a new ribbon for it, but it
looks like instead of
replacing the ribbon as a cartridge, you pull the whole ribbon out of
the screwed in case and then have to pack a new one in. The pinch
Yep :-(
-tony
4:37 p.m.
On Jun 20, 2014, at 2:23 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Ah... It probably is a Centroics 703. Is it the right
colour ir is it
'battleship grey' like the computer? IIRC the rist Radio Shack 'Line
Printer' (which was not a ture line pritner, of course) was actually a
Centroics 703 with grey case mouldigns. No internal changes at all.
Instead of me trying to describe it, how about I provide some color photos? :-)
http://imgur.com/a/yUNL1
If this is the printer I am thinking of (and from your
description of the
ribbon I think it is), the carriage motor is an AC shaded pole thign that
runs all the time. It drives a belt acorss the printer. Solenoids in the
carriage grab the top or bottom run fo the belt to move the carriage. Odd..
No it uses a normal belt system that isn't running all the time and is firmly
connected to the print head. The only thing that runs all the time is the large fan in it.
It's not a Radio Shack model, it has lots of buttons on the front. It does look very
similar though.
Were you not supposed to ever replace the belt, just re-ink it in place? What about when
the pinch rollers for the ribbon wear out?
21 Jun
21 Jun
12:39 p.m.
On Jun 20, 2014, at 2:23 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
The casign looks like that of the Centronics 703, but...
Ah... It probably is a Centroics 703. Is it the
right colour ir is it
'battleship grey' like the computer? IIRC the rist Radio Shack 'Line
Printer' (which was not a ture line pritner, of course) was actually a
Centroics 703 with grey case mouldigns. No internal changes at all.
Instead of me trying to describe it, how about I provide some color
photos? :-)
http://imgur.com/a/yUNL1 If this is the printer I am thinking of (and from
your description of the
ribbon I think it is), the carriage motor is an AC shaded pole thign that
runs all the time. It drives a belt acorss the printer. Solenoids in the
carriage grab the top or bottom run fo the belt to move the carriage. Odd..
No it uses a normal belt system that isn't running all the time and is
firmly connected to the print head. The only thing that runs all the
time is the large fan in it. It's not a Radio Shack model, it has lots
of buttons on the front. It does look very similar though.
Were you not supposed to ever replace the belt, just re-ink it in
place? What about when the pinch rollers for the ribbon wear out?
I have looekd i nthe 703 service manual, it's annoying. Most faults were
fixed with repair kits which cotnaiend subassemblies and the fixign
screws for them (at least there is a scheamtic in the manual).
Anyway, certainyl the raw ribbon can be remvoed and replaed separately.
The procedue for dismantlign the ribbon system starts by doign that, then
unscrewign the husing fro mthe cvhassis. I didn't download the user
manual, but I guess you replaed jsut the ribbon. Messy job...
As for the rolelrs I think you replaced them as part of the bracketry they
were mounted on. I don't normally worry about thigns liek that, the
chasnces of fidnign NOS repair kits or spares is remote. I eitehr repari
the origianl aprts or make new oens from scratch.
-tony
23 Jun
23 Jun
1:04 p.m.
On Jun 21, 2014, at 12:39 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I am pretty sure the 703 is the one with this rather
strange
belt-grabbing mechanism. In which case you don't have a 703. I wonder if
the casing on yours was replaced using bits from a 703, and that's why
the model number is blacked out. Waht you have I do not know..
I added some more pictures to the album: http://imgur.com/a/yUNL1
I looked all over the exposed PCB to see if they were any numbers on it, but didn't
see anything. I thought it was interesting that it uses a plastic ribbon with lines on it
to position the head optically. The ears on the parallel connector are also rather odd,
they're too big to fit a normal cable.
I was also able to hook it up to a computer and print on it. It has no lowercase! I'm
amazed at how cheap/short-sighted they were to not put in lowercase. It also forces a line
feed after a carriage return. I've heard that some Centronics models can be modified
to not force a line feed by removing a resistor, but I haven't seen any specifics of
*what* resistor, and since my printer is some weird hybrid, I don't know if that
information even applies.
24 Jun
24 Jun
2:13 p.m.
I looked all over the exposed PCB to see if they were
any numbers on
it, but didn't see anything. I thought it was interesting that it uses a
IIRC, the carriage PCB in the 703 has postions for some optical sensors,
They are not fitted in the 703 (which simply uses this PCB to connect up
the printhead), but your pritner might be a related model.
plastic ribbon with lines on it to position the head
optically. The ears
on the parallel connector are also rather odd, they're too big to fit a
normal cable.
Looking at the kinks in those locking clips, I think it's a normal
Microribbon connector that's been bent a bit.
-tony
2:15 p.m.
On Mon, Jun 23, 2014 at 2:04 PM, Chris Osborn <fozztexx at fozztexx.com> wrote:
I was also able to hook it up to a computer and print
on it. It has no
lowercase! I'm amazed at how cheap/short-sighted they were to not put in
lowercase.
That's not due to being cheap or short-sighted, it's due to product
positioning. They either offered lower case as an option, or as a more
expensive model, I don't rememer which. That was standard practice in the
printer industry for many years.
2:28 p.m.
On Jun 24, 2014, at 5:15 PM, Eric Smith <spacewar at gmail.com> wrote:
On Mon, Jun 23, 2014 at 2:04 PM, Chris Osborn
<fozztexx at fozztexx.com> wrote:
For one thing, you need more pixels for lower case. Early dot matrix printers had, I
think, 5x7 matrix for the uppercase only model, but needed at least 7x9 for lowercase.
(Then there were printers with something like 16x16 matrix, for printing Japanese text.)
paul
I was also able to hook it up to a computer and
print on it. It has no
lowercase! I'm amazed at how cheap/short-sighted they were to not put in
lowercase.
That's not due to being cheap or short-sighted, it's due to product
positioning. They either offered lower case as an option, or as a more
expensive model, I don't rememer which. That was standard practice in the
printer industry for many years. 
3:37 p.m.
On 06/24/2014 02:28 PM, Paul Koning wrote:
For one thing, you need more pixels for lower case.
Early dot matrix
printers had, I think, 5x7 matrix for the uppercase only model, but
needed at least 7x9 for lowercase. (Then there were printers with
something like 16x16 matrix, for printing Japanese text.)
Surely you remember the lowercase mod for the ADM-3A terminal! 5x7
matrix, looked like hell, but was readable. FWIW, the veneered and
generated 2513 character generator had a katakana option as well.
There were 5x7 dot matrix printers with lowercase and no descenders.
--Chuck
25 Jun
25 Jun
12:24 p.m.
For one thing, you need more pixels for lower case.
Early dot matrix
printers had, I think, 5x7 matrix for the uppercase only model, but
You can get a sort-of lower case font out of a 5*7 character generator,
but it doesn't look nice. To get an apporxiamtion to descenders, you have
a baseline that is higher for such characters. Readable, but...
Omewhere I have a portable thermal printing terminal which prints lower
case as small capitals. Odd.
I also have an old video terminal (old enough that it uses shfit
regiusters for the video memroy) where the dispaly section could handle
lower cases (I suspect without true descenders, but it's been a long time
since I used it) but hhe keyboard was upper case only. The service
manualk gave 2 modfiications to the keyboard to let it generate lower
case Of course I hacked mine . IIRCL it involved wiring up a couple of
TTL chips and patchign them into the keyboard encoder circuit.
needed at least 7x9 for lowercase. (Then there were
printers with
something like 16x16 matrix, for printing Japanese text.
There were also printers that did multiple passes with the position of the
head relative to the paper moced. The DEC LA100 has a solenoid mechanism
to moce the head up and dowbn. The Sanders 12/7 and 700 series move the
paper in fractional-dot icrements -- I think at least one font uses 8
pases and thus has an effective vertical resolution of 56 dots (7 pin
head).
-tony
24 Jun
24 Jun
2:55 p.m.
On Tue, 24 Jun 2014, Eric Smith wrote:
That's not due to being cheap or short-sighted,
it's due to product
positioning. They either offered lower case as an option, or as a more
expensive model, I don't rememer which. That was standard practice in the
printer industry for many years.
When the TRS-80 [model 1] first came out, it did not have lower case.
So, why should its printer?
It was relatively trivial to modify for it (including adding one more RAM
chip), and the character generator included a crude lower case font.
And, on the "line feed forced on carriage return" - all Radio Shack
printers were configured that way.
3:26 p.m.
On Jun 24, 2014, at 2:55 PM, Fred Cisin <cisin at xenosoft.com> wrote:
When the TRS-80 [model 1] first came out, it did not
have lower case.
So, why should its printer?
It was relatively trivial to modify for it (including adding one more RAM
chip), and the character generator included a crude lower case font.
And, on the "line feed forced on carriage return" - all Radio Shack
printers were configured that way.
Except my printer isn't a Radio Shack rebranded version. It's a genuine
Centronics.
3:10 p.m.
On 24 June 2014 22:15, Eric Smith <spacewar at gmail.com> wrote:
On Mon, Jun 23, 2014 at 2:04 PM, Chris Osborn
<fozztexx at fozztexx.com> wrote:
That's not due to being cheap or short-sighted, it's due to product
positioning. They either offered lower case as an option, or as a more
expensive model, I don't rememer which. That was standard practice in the
printer industry for many years.
I remember a feature of dot matrix printers being "has true
descenders". Which I don't think, say, the Decwriter II had.
--
Yoyodyne Propulsion Systems: "The Future Begins Tomorrow"
Visit us at: http://www.yoyodyne-propulsion.net
--------
"When a true genius appears in the world, you may know him by this
sign, that the dunces are all in confederacy against him." -- Jonathan
Swift
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