My name is Dale, I live in Canberra, Australia, and I'm new to this group. I've recently acquired a Teletype Model 28 receive only machine that was apparently used at a NASA tracking station near here. It hasn't been used for probably 40 years, but it's in good condition and basically works after cleaning and lubrication. 

I'm running it on a 75 baud 60 mA current loop and at 110 VAC 60 Hz through a sine-wave inverter because power here is 50 Hz. It prints RYRY... more-or-less perfectly with only the very occasional X instead of a Y. However does have a problem with the type box positioning and it consistently misplaces characters based on the previous character. For example (char input on left, prints on right):

MMMNMHMspace MMMNMMMspace  (space is the space bar char)   here the H is printed as an M

VVVCVPVI                VVVCVVVI                       here the P is printed as a V

BBBDBZBE               BBBDBBBE                     here the Z is printed as a B

GGGRGLGlf              GGGRGGGlf     (lf is the line feed char) here the L is printed as a G

Looking at the character placement in the type box, the problem occurs for all rows and the problem lines up with the two columns

of characters either side of the centre line in the type box which are the two columns corresponding to bits 4=space & 5=mark:

H             T

Y              Z

P              L

Q             W

The problem seems to be with bit 4 going from mark to space if bit 5 is mark. There is no problem with bit 4 = space

if bit 5 goes from space to mark. The state of bits 1,2 and 3 don't seem to matter. The end result of all of this is that the incoming message

is corrupted and the machine is not very usable.

I've checked the code bars on both sides of the machine and they are correct for all characters, so I think the selector mechanism is working properly. The problem seems to be in the type box positioning mechanism, however I'm not familiar with the M28 machine and don't want to just pull it apart

blindly looking for a problem because I'll never be able to put it all back-to-together again!

I'm hoping someone in the group can point me in the direction of the likely problem and how to fix it! I can send a photo of the printout showing the results of the QUICK BROWN FOX... message if that is helpful.

Many thanks and sorry for the long email.

Regards

Dale VK1DSH