SOS! Tektronix 4006-1 terminal on the fritz right before the show!

[stepleton]

All right, it looks like the keyboard is repaired (for now)! I replaced the 9601 retriggerable one-shot, which fixed the key-repeat problem (keyboard underclocking apparently wasn't the cause there; C2 was almost exactly 2.2uF when I pulled it out and checked). But there was still a problem: it's an ASCII keyboard, but bit 5 was (often) inverted, a sign of something failing in the maze of logic that implements the character-changing action of the shift key. After poking around, I found a 49-year-old 7400 with one output stuck at +2V always. With that replaced, it seems like we're back in business.

Combined with the 74151 and 74154 that I replaced in the keyboard months ago, I've replaced four of the keyboard's 13 ICs. The first two were corroded to heck (did someone spill coffee once upon a time?), but these latest failures seem to me like good examples of what I think of as the Jerry Walker effect: he's often pointing out in his videos how veteran ICs can fail after a short period of work following a long retirement --- they're just frail. So it goes.

The villains: https://photos.app.goo.gl/QJTvddHFssnUoUGx8
Fairchild(?) and AMD parts.

Thanks for all the advice and encouragement! I hope things hold up now through the end of the show this weekend...

 

[nikola-wan]

Tom, I found a couple of videos of the Cambridge Retro Computer Festival 2023 posted on youtube.

One of them had a couple of closeups of your Tektronix 4006:






and a different one showed both of your 4051s and 4006 - but didn't have any closeups:




Nice images on your 4006! Congratulations on your repairs!

 

[stepleton]

Thanks! I know the museum itself was filming as well; they interviewed a few of the exhibitors, including me. They'll probably have longer shots of the 4006-1 drawing, I think.

 

[nikola-wan]

I just found your Flood Gun animation video and your comment about the X-Y Origin Shift. Page 3-10 in the 4006-1 service manual indicates there is a CAL jumper that disables Origin Shift. I see the same thing in the 4052/4054 Technical data and Figure 12-4 Origin Shift in the 4054 Display theory diagrams the movement of the beam down and left from RESET (?) to CENTER-0 which is the CAL strap on the 4052 and 4054 display circuits that disables the Origin Shift.

However for filming your animations - I would probably recommend that you not disable the Origin Shift circuit. I caused burn in on my Option 31 color DVST by preventing the screen from erasing while I was trying to convert the PLOT 10 spacelab images to R12 format with my BASIC program

I think you used the four small circles in the corner during post processing of each frame to recenter each image. I like that Flood Gun animation video!

I wonder if I can create an Option 30 BASIC program that will do that Flood Gun animation - live on the 4054A!