5 ms·

Xerox Alto Restoration Part 2: Firing up the monitor [video]

107 points by andars 10y ago

kens 10y ago
Summary: we got the monitor working (using a signal generator from the Seattle Living Computer Museum (thanks!)), but the display is very dim, probably due to the old CRT. Does anyone in the bay area have experience with CRT rejuvenation?
- crististm 10y ago
  Back in the days, folks used to slightly increase the filament voltage, from 6.3V to 7V or more. Sometimes you could even recover the CRT and it would work with the nominal filament voltage. This is a really unique piece of hardware and of course you might want to try this technique only if you have no choice.
- userbinator 10y ago
  There's other things that could cause a dim display, not necessarily just a worn tube. Low anode voltages is another possibility that comes to mind. The various television/electronics forums may have people willing to assist with troubleshooting. If it's really the tube, and it's a truly rare custom tube and not just something you might be able to find a suitable replacement for, maybe these guys can help: http://www.earlytelevision.org/crt_rebuild.html http://www.earlytelevision.org/crt_rebuild.html
  - Animats 10y ago
    I was about to post a link to them. Full CRT rebuilding is a reasonable option for a B/W tube. (Color requires very precise electron gun alignment so the shadow mask lines up with the dots, and that's hard to do as a repair.) The last commercial CRT rebuilder for ordinary TVs in the US closed in 2010.[1] But there's still a company that does it for military display devices that need to be kept going.[2] "We are your obsolescence solution now and in the future." It really is a custom tube. PARC built the first tubes in-house (PARC was also a copier R&D facility, so they could build precision optoelectronics) but then sent the job out for production. [1] http://www.tvtechnology.com/miscellaneous/0008/last-lone-wolf-crt-rebuilder-closing/206279 http://www.tvtechnology.com/miscellaneous/0008/last-lone-wol... [2] http://www.thomaselectronics.com/ http://www.thomaselectronics.com/
- mikejmoffitt 10y ago
  If you wait for half a year, I own two rejuvinator units and have used them to restore some tunes. Once I move to the Bay Area I'd be happy to lend them out.
- deleted 10y ago
  [deleted]
amq 10y ago
Reminds me the scene in Alien where they turn on the damaged Ash.
epberry 10y ago
I'm really loving following this and I admire the tenacity this must take. For example... Screen brightness too low? Okay, just whip out some ancient circuit diagrams, trace them to find the capacitor at fault, find that capacitor on the board, desolder it, test it, find that it's faulty, resolder a new one. Well that helped but it's not much better sigh. Now examine the switch, CRT tube, etc. And here I've been known to throw in the towel when having 'this' issues in JS.
- Animats 10y ago
  I do that kind of thing for antique Teletype machines.[1] The discouraging projects are when you get all the way to a working machine and the typing quality is still too bad to be usable. That machine had been dropped at some point. I could do more work on it, but I could get a better one on eBay.[2] [1] http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html [2] http://www.ebay.com/itm/272286062507 http://www.ebay.com/itm/272286062507
  - userbinator 10y ago
    Teletypes are interesting because they're basically mechanical UARTs. Watching the mechanisms in them operate still fascinates me.
    - dghughes 10y ago
      You may enjoy Bill Hammack's video "IBM Selectric Typewriter & its digital to analogue converter" https://www.youtube.com/watch?v=bRCNenhcvpw https://www.youtube.com/watch?v=bRCNenhcvpw
      - Animats 10y ago
        The IBM Selectric is a magnificent piece of engineering, and close to being the last complex piece of mass-manufactured mechanical logic . The only electrical part is a motor. But it's not the ancestor of the computer printer. The Selectric's main ancestor is the Blickensderfer_typewriter [1], from 1892. This used a curved type element rather than a typeball, but had a similar method of turning key presses into typing element positions. As with the Selectric, the font could easily be changed. There was a proportional-spacing successor to the Blickensderfer, the Vari-Typer, and IBM imitated that, too, with the IBM Selectric Composer. The Selectric had a moving print head rather than moving paper, with cables on moving idlers used to transmit position to the print head. That mechanism is from the Teletype Model 28/35, from the early 1950s. Moving the print head rather than the paper was a Teletype concept - it worked much better with roll paper, and the machine was narrower. The Selectric mechanism was not designed for electrical inputs and outputs. The add-on mechanism for that was an afterthought, and kind of a hack. The unit had to be built into a table, and the mechanism for the keyboard extended below the tabletop. IBM and Remington had previously built typewriters with electrical I/O, and those were used with some early mainframe computers. Many computers, before and after the Selectric, used Teletype machines as I/O devices. That lasted until daisy-wheel printers and cheap CRT terminals were invented. (Mechanical line printers have a completely separate history. They descend from the Potter Flying Typewriter.[2]) [1] https://en.wikipedia.org/wiki/Blickensderfer_typewriter https://en.wikipedia.org/wiki/Blickensderfer_typewriter [2] https://www.computer.org/csdl/proceedings/afips/1952/5041/00/50410106.pdf https://www.computer.org/csdl/proceedings/afips/1952/5041/00...
protomyth 10y ago
Is there some history of refresh rates around? I'm really curious why they used a "weird" rate on the Alto.
- kens 10y ago
  The Alto has a "weird" refresh rate because it uses a portrait-format display with 875 scan lines, compared to a "normal" display with 525 lines. The higher scan rate stresses the horizontal drive circuitry and can cause overheating problems.
  - protomyth 10y ago
    So, they didn't do what portrait monitors do today? Interesting, thanks for the information.
    - ams6110 10y ago
      Meaning what, a landscape or wide monitor turned on its side?
      - protomyth 10y ago
        yes
    - kens 10y ago
      "what portrait monitors do today" - you mean just turn the monitor sideways? That would have kept the scan rate lower, but the Alto would need to send the pixels a column at a time rather than a row at a time. That would be tricky to do (keeping in mind this was all done with TTL chips and microcode, so they wanted to keep things simple).
      - hcs 10y ago
        > but the Alto would need to send the pixels a column at a time rather than a row at a time. That would be tricky to do Couldn't the buffer just be column-major?
frik 10y ago
Was the camera operator x-rayed by the high voltage arc in the tube? (7:47 in the video) At 7:35 he filmed in a close up the caution label on the tube backside with x-ray warning fine print X-RAY WARNING: When picture tubes are operated above 16 kilovolts, and when personal exposure is prolong at close range, special shielding precautions against X-ray radiation may be needed.

107 points by andars 10y ago

kens 10y ago

Summary: we got the monitor working (using a signal generator from the Seattle Living Computer Museum (thanks!)), but the display is very dim, probably due to the old CRT. Does anyone in the bay area have experience with CRT rejuvenation?

crististm 10y ago
Back in the days, folks used to slightly increase the filament voltage, from 6.3V to 7V or more. Sometimes you could even recover the CRT and it would work with the nominal filament voltage. This is a really unique piece of hardware and of course you might want to try this technique only if you have no choice.
userbinator 10y ago
There's other things that could cause a dim display, not necessarily just a worn tube. Low anode voltages is another possibility that comes to mind. The various television/electronics forums may have people willing to assist with troubleshooting. If it's really the tube, and it's a truly rare custom tube and not just something you might be able to find a suitable replacement for, maybe these guys can help: http://www.earlytelevision.org/crt_rebuild.html http://www.earlytelevision.org/crt_rebuild.html
- Animats 10y ago
  I was about to post a link to them. Full CRT rebuilding is a reasonable option for a B/W tube. (Color requires very precise electron gun alignment so the shadow mask lines up with the dots, and that's hard to do as a repair.) The last commercial CRT rebuilder for ordinary TVs in the US closed in 2010.[1] But there's still a company that does it for military display devices that need to be kept going.[2] "We are your obsolescence solution now and in the future." It really is a custom tube. PARC built the first tubes in-house (PARC was also a copier R&D facility, so they could build precision optoelectronics) but then sent the job out for production. [1] http://www.tvtechnology.com/miscellaneous/0008/last-lone-wolf-crt-rebuilder-closing/206279 http://www.tvtechnology.com/miscellaneous/0008/last-lone-wol... [2] http://www.thomaselectronics.com/ http://www.thomaselectronics.com/
mikejmoffitt 10y ago
If you wait for half a year, I own two rejuvinator units and have used them to restore some tunes. Once I move to the Bay Area I'd be happy to lend them out.
deleted 10y ago
[deleted]

amq 10y ago

Reminds me the scene in Alien where they turn on the damaged Ash.

epberry 10y ago

I'm really loving following this and I admire the tenacity this must take. For example... Screen brightness too low? Okay, just whip out some ancient circuit diagrams, trace them to find the capacitor at fault, find that capacitor on the board, desolder it, test it, find that it's faulty, resolder a new one. Well that helped but it's not much better sigh. Now examine the switch, CRT tube, etc. And here I've been known to throw in the towel when having 'this' issues in JS.

Animats 10y ago
I do that kind of thing for antique Teletype machines.[1] The discouraging projects are when you get all the way to a working machine and the typing quality is still too bad to be usable. That machine had been dropped at some point. I could do more work on it, but I could get a better one on eBay.[2] [1] http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html [2] http://www.ebay.com/itm/272286062507 http://www.ebay.com/itm/272286062507
- userbinator 10y ago
  Teletypes are interesting because they're basically mechanical UARTs. Watching the mechanisms in them operate still fascinates me.
  - dghughes 10y ago
    You may enjoy Bill Hammack's video "IBM Selectric Typewriter & its digital to analogue converter" https://www.youtube.com/watch?v=bRCNenhcvpw https://www.youtube.com/watch?v=bRCNenhcvpw
    - Animats 10y ago
      The IBM Selectric is a magnificent piece of engineering, and close to being the last complex piece of mass-manufactured mechanical logic . The only electrical part is a motor. But it's not the ancestor of the computer printer. The Selectric's main ancestor is the Blickensderfer_typewriter [1], from 1892. This used a curved type element rather than a typeball, but had a similar method of turning key presses into typing element positions. As with the Selectric, the font could easily be changed. There was a proportional-spacing successor to the Blickensderfer, the Vari-Typer, and IBM imitated that, too, with the IBM Selectric Composer. The Selectric had a moving print head rather than moving paper, with cables on moving idlers used to transmit position to the print head. That mechanism is from the Teletype Model 28/35, from the early 1950s. Moving the print head rather than the paper was a Teletype concept - it worked much better with roll paper, and the machine was narrower. The Selectric mechanism was not designed for electrical inputs and outputs. The add-on mechanism for that was an afterthought, and kind of a hack. The unit had to be built into a table, and the mechanism for the keyboard extended below the tabletop. IBM and Remington had previously built typewriters with electrical I/O, and those were used with some early mainframe computers. Many computers, before and after the Selectric, used Teletype machines as I/O devices. That lasted until daisy-wheel printers and cheap CRT terminals were invented. (Mechanical line printers have a completely separate history. They descend from the Potter Flying Typewriter.[2]) [1] https://en.wikipedia.org/wiki/Blickensderfer_typewriter https://en.wikipedia.org/wiki/Blickensderfer_typewriter [2] https://www.computer.org/csdl/proceedings/afips/1952/5041/00/50410106.pdf https://www.computer.org/csdl/proceedings/afips/1952/5041/00...

protomyth 10y ago

Is there some history of refresh rates around? I'm really curious why they used a "weird" rate on the Alto.

kens 10y ago
The Alto has a "weird" refresh rate because it uses a portrait-format display with 875 scan lines, compared to a "normal" display with 525 lines. The higher scan rate stresses the horizontal drive circuitry and can cause overheating problems.
- protomyth 10y ago
  So, they didn't do what portrait monitors do today? Interesting, thanks for the information.
  - ams6110 10y ago
    Meaning what, a landscape or wide monitor turned on its side?
    - protomyth 10y ago
      yes
  - kens 10y ago
    "what portrait monitors do today" - you mean just turn the monitor sideways? That would have kept the scan rate lower, but the Alto would need to send the pixels a column at a time rather than a row at a time. That would be tricky to do (keeping in mind this was all done with TTL chips and microcode, so they wanted to keep things simple).
    - hcs 10y ago
      > but the Alto would need to send the pixels a column at a time rather than a row at a time. That would be tricky to do Couldn't the buffer just be column-major?

frik 10y ago

Was the camera operator x-rayed by the high voltage arc in the tube? (7:47 in the video) At 7:35 he filmed in a close up the caution label on the tube backside with x-ray warning fine print X-RAY WARNING: When picture tubes are operated above 16 kilovolts, and when personal exposure is prolong at close range, special shielding precautions against X-ray radiation may be needed.