29 Apr
2005
29 Apr
'05
6:18 p.m.
I am looking for troubleshooting tips for a 33 teletype.
I'm testing in local mode and am getting incorrect characters=20
on (almost) every keypress. The characters will change even=20
with repeated pressings of the same key. I am pretty sure the=20
keyboard is outputting the correct codes.
I presume you know that the keyboard outputs parallel ASCII, which is
serialised by the distributor.
In 'line' mode, full duplex. the transmitter (keyboard + distributor)
appears to be a normally closed switch between the 2 Tx loop terminals.
It should be very easy to turn that into something approximating to RS232
using a couple of 9V batteries and a 1k (or so) resistor :
+-------------------+
| |
------- 9V /
--- \ 1k
| /
| \
| |
| +------ TxD on Rs232 port
| |
+-------------------)------ Signal Ground on RS232 port
| |
| o
------- 9V Tty TX terminals
--- o
| |
+-------------------+
This would at least tell you which side of the Teletype was malfunctioning.
[...]
Is it possible to disconnect the motor drive belt and
rotate the shaft=20
manually to get a closer look at what is happening mechanically?
I find it easier to electrically stop the motor and turn the machine over
using the motor cooling fan (remove the air deflector plate if you find
it helps). Some machines have a motor fuse on a bracket at the rear left
corner of the typing unit, behined the receiving magnet. If you have
that, just take the fues out. Otherwise, you can disconnect the motor
leads at the starting relay (if used), or remvoe the pins from the Molex
plug, or something like that.
It's very hard to see what is going on in the
selector area with the
shaft spinning so fast.
By the way, my drive belt is somewhat loose. Is there still a source
for these? Or maybe an adjustment for tightening?
I probably so still have a spare belt, but I am the wrong side of the Pond...
Yes there's an adjustment. Loosen the 4 motor mouting screws (2 on each
stap that holds the motor down) and rotate the motor housing to tension
the belt.
-tony