From: ard(a)p850ug1.demon.co.uk (Tony Duell) (from the description below, I assume a PDP8). If it _is_ a PDP8, do you have the reader control relay mod fitted correctly? If not, then you _will_ drop characters I think. My computer is an 8/L. I do not have the relay fitted at all. After a careful examination of the schematic and manuals, this relay only forces TTY power on, in LINE mode (this is redundant if the TTY is already on and prepared to read a tape), and also forces 115V to the distributor trip coil so that a tape will immediately start reading if present. Without the relay a manual start is required by simply flipping the reader lever to "Start". Everything gets up to speed after one or two characters of leader no matter how the reader is initiated. No characters will be dropped since the program will loop indefinitely at the usual KSF, JMP.-1 until a character is assembled and sent to the TTY receiver card. ratchet wheel teeth in the reader. But that would cause problems once (or n times) for every revolution of that wheel (and the drive sproket) -- Quite. That's why I'm scratching my head! but some of them are corrupted to 0's? Yes, when an error occurs while printing the test tape I can "hear" the nonprinting character being sent to the typing unit (it "jumps" but nothing appears on the paper) and the next consecutive char is then printed correctly. of the tape holes -- check this), or the contacts are sometimes not making properly. Agreed. They look centered to me (but what IS the definition of "centered" i.e. at what point in the read cycle? The tape and pins do not seem perfectly stationary with respect to one another during the read cycle.) The manual shows that the sprocket wheel should be rotated forward to take up the slack against the detent at which point the pins are centered in the holes. IF I'm reading this right. Actually they show a "Gate Flash" that looks like a hole on the side of the sprocket, which does not exist in my reader. should then send all 1's. Check that it does (use the PDP8 for this with a similar program to yhe one you've written already, just get it to halt if the character is not all 1's). Let it run for many minutes. Excellent suggestion, thank you. I will try this right away. Who's Heath Robbinson? I always liked Rube Goldberg's inventions... for the flashgun. Make the room dark, hold the shutter open on B, let it run 4) When the flash fires, close the shutter, turn everything off 5) Develop the film and hope that it shows you what the problem is. -tony Sounds awfully complicated. Perhaps I can do this with my Sony digital camera if it has a sync input! thanks for the tips -Charles