11 Nov
2002
11 Nov
'02
8:57 p.m.
From: ard(a)p850ug1.demon.co.uk
Hi
I think you need to make this point clearer. When a character
is punched, the same character is miss printed on the platen?
This is how I read his original post.
This tells me it is something sticking in the linkage that goes
between the code bars and the print head( or he has it installed
wrong but that doesn't explain why it starts working with repeats ).
I would remove the print assembly and put it in some solvent
while moving the levers. Then clean it off/dry it and re-oil
it. You most likely have some dry oil that is sluggish. Getting
oil into the right place will take a bit.
In the service( military ), we used to clean things in a bath
of water and heavy detergent. This was done in an ultrasonic
cleaner. We'd then rinse and bake it at about 150F for a few
hours. Then Re-oil/grease, place on test bench and fine adjust.
I suspect that a good dish washing liquid would work.
You can find manuals at:
http://www.pdp8.net/pdp8cgi/query_docs/query.pl?Search=teletype&stype=P…
rd&fields=id%2Ctitle%2Cdate&debug=0&table=pdp8docs&orderby=sort%2Ctitle
You'll need to paste it back together after the mail chops it.
Dwight
Any Teletype ASR33 experts out there ? I have a couple
of problems with a teletype that recently came my way.
I believe the ASR33 manauls are available on a web site somewhere. If
you don't have them as printed books, then you want to get these files
and print them. They make life a lot easier. OK, I did a complete
strip-down, clean, oil, reassemble and adjust job on an ASR33 without the
manuals (and with never having seen the manuals), but then I tend to do
crazy things like that...
i) When I type a character from the keyboard in local
mode, something else gets printed. What gets printed
is not consistently the same character. I've watched
the selector mechanism while I hit rubout (all marking
codebars) and I can see that the codebars are not
being consistently selected betwee key presses:
sometimes I get 5 of them, sometimes 6 and
occasionally all 8. The high order bits seem to be
worst affected by this inconsistency. However if I
hold down the repeat key and select a character, the
right codebars are being selected. I punched a number
of characters onto tape to verify this and they seem
to be punching OK. This suggests to me that this isn't
If the character _always_ punches correctly, then the right codebars are
being selected. So I assume this is not the case.
Basically, there are 3 possible problem areas :
1) The keyboard contacts are not closing correctly, so the parallel data
output of the keyboard is incorrect.
2) The distributor disk (rear right of the typing unit) is not correctly
serialising the data from the keyboard. Unlikely, but possible.
3) The selector unit (rear left of the typing unit) is malfunctioning,
and is not correclty responding the receiving magnet.
I would check (3) first. It may need to be removed, dismantled, cleaned,
and re-lubricated. It's not uncommon for parts to stick on old, gummy,
lubricant.
an electrical problem since whatever code the
keyboard
is sending is eventually being sensed correctly.
ii) In addition to i) above, even if I do get all the
codebars moving as required, the wrong characters are
being printed. I removed the carriage, cleaned and
oiled it and replaced it but this hasn't helped.
How did you clean it? I have found that soaking compete assemblies in
solvent doesn't help much. You really have to take all the parts apart,
clean them, and then re-assemble them. If yoy've done this, then there
are a lot of sdjustment you'd have to set up.
A character decoding problem must be in the carriage. There are 4 parts
to the decoder mechanism :
2 bits -> one of 4 levels of lift of the type cylinder
1 bit -) rotate cylinder left or right
2 bits -> one of 4 angles (pairs of characters) of rotation of the cylinder
1 bit -> an extra 1 character angle rotate (it moves the selector bars
for the previous rotation selection slightly...).
Figure out which mechanism is malfunctioning by comparing the position of
the character you get with the position of the character you should be
getting. Then work out what's not operating properly.
-tony