Digibarn Alto Part 3: Restoring the CRT Monitor
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- Опубліковано 17 жов 2024
- The rat-infested Digibarn monitor isn't even meant to be connected to an Alto, and does not work either. But we find a way to retrofit it to the Alto, and find that a tiny light bulb buried in the high voltage circuitry is the cause of the failure. More details about what a bulb is doing in the circuit on Ken's blog (and don't believe the inane comments, it is not used a fuse): www.righto.com/...
"the filament is filamenting" best line yet from these videos :)
"Hey, the monitor doesn't work because the light bulb burned out"
"What are you talking about? It's a CRT, not a light bulb."
"Trust me, the light bulb burned out."
Interesting that the CRT in the digibarn unit is so much fresher than the original on your guy’s Alto. Must have a lot less run hours on the CRT I would imagine. Once again another excellent repair you guys! Can’t wait to see the second Alto back in action!
Beautiful! Could the incandescent lamp be used as a soft-start NTC (and be replaced by one)?
Actually, I mispoke, that's a positive coefficient resistor. Starts with low resistance, and it goes up when the filament heats up. So, similar idea, but opposite direction compared to a NTC.
Nice work guys! CRT repairs are always finicky because of the high currents involved. Great job bringing this back from the grave!
These videos are always so excellent. I learn so much each time I watch. Wish you guys had a repair shop out in my neck of the woods!
I really enjoy being part of the trouble shooting and fixing journey. Thanks for creating these types of videos.
Your friends are so excellent. Your show is awesome, and the lasersound and piano scale and bulb and everything … excellent
That monitor makes very very straight sharp high contrast lines!
Thats typical for a CRT.
It was a long time since I noticed that. Haven't had one in several years now. When we moved to flat panels I never looked back, but now that I do, I can see the value of these sharp lines.
Nice repair! That CRT looks pin sharp!
I just replaced the CRT on my new-to-me Lisa. The original CRT was P7 phosphor like your Alto displays, the replacement is a more modern P4. I was worried it would make the screen look odd, but it works great!
considering the previous repairs that you did, this was a piece a cake.
No, the display is not from a Dolphin. We had five Dolphins (aka D0) at The RAND Corporation, and the monitors were standard 4:3 b&w monitors, not the strange vertical ones. They were about 19".
We had five Dolphins at The RAND Corporation, and that monitor didn't come from a Dolphin...at least, not from a Dolphin like ours. Our Dolphin monitors were rather larger, and had a 4:3 ratio like a standard NTSC TV set - higher resolution of course. The things ran Interlisp and Smalltalk, so they were all about the graphics and screen real estate. Hence the larger monitors.
I heard you mention that this might be a Dolphin monitor. It isn't. The RAND Corporation, when I worked there in the '70s-'80s, bought five Dolphin (D0) machines from Xerox to run Interlisp. The under-desk machine had about the form factor of an Alto but looked quite different. It had a 4-digit red seven-segment LED display showing which microcode state the machine was in...helped no end in diagnosing boot problems. The monitors were 19-inch B&W displays that had a "normal" (4x3) form factor rather than the vertical display of an Alto. Since Interlisp and Smalltalk (which we also had, gratis, because we organized Xerox' VAX-750 file server software into a real distribution for them, which also netted us a 3Mbit PUPNET VAX interface board signed by Bob Metcalfe) were both windowing systems, that extra screen real estate came in VERY handy! I wish you could find one of those D0s somewhere. RAND has no idea what happened to theirs.
Excellent video Marc, I'm always looking forward to more of these!
Hi, really amazing your guys restoring's videos! Soldering on a light bulb glass makes notice me how I'm begginer into soldering skills! Great work!
Anybody else wonder what this house looks like? It seems like a nice place to live.
😎👍👍😁
Yes, this is very interesting series, please GIVE US MORE! :)
Wow. Soldering acrobatics for sure. now THAT's a feat. should write to Hackaday for that one, right there.
let me jump in my time machine and tell hackaday folks about this video hackaday.com/2017/10/15/xero-alto-crts-needed-a-tiny-lightbulb-to-function
Love the light sabre effect
Thanks for theses videos , I'm really enjoying this series !!
yay for the soldering!, that was quite amazing that solder you did there! :O :O :O
I can't get enough of this.
Marc you said "gave the monitor a bath" could you expand on the procedure you use for entire assemblies like the monitor?
This was mostly in jest. I think I cleaned this one up mostly with isopropanol. As usual, the more you can take apart, the best you can clean. On occasion I have done full bath in Simple Green, mostly for mechanical assemblies that were too hard or too risky to take apart, like the model 19 Teletype print carriage. Some people have put assemblies in dish washing machines (!), and I sometimes clean boards in water + simple green, like I did for a couple of the worst boards of the Digibarn Alto here. Needless to say, you have to check there are no water sensitive parts, and careful immediate drying with a hair dryer is a must.
@@CuriousMarc Thank you for the detailed reply!
When soldering under the microscope you should maybe use a powerful fume extractor to not have the fumes hit the lense. I have taken apart one that accumulated years of fume, its really not good.
Over here in Cambridge I look at the mere 1kV stuff present at the pointy end with cheap (x10 or x100) probes but then the 'scopes are cheap too
Yes, for the anode acceleration voltage we'd absolutely need the probe, but for the grids at around 600V we could get away with a my regular DVM that has a high voltage setting. Better safe than sorry though, and that was a great plug to show off Carl's mighty lightsaber probe.
Great repair, well done. And so brave too! :)
A light-bulb used as a resistor? That’s crazy!! I mean, I get why they did it - low resistance when first powered on allows greater current, which you need at first, and then the resistance goes up quickly to limit the current. But still... A light bulb?! Crazy!
There was such a large market and such price pressure on analog TV CRT circuits for such a long time that they had been refined to an incredible level. I have rarely seen more analog high voltage and high current trickery to save a 10c component than in TV deflection circuits. The use of lamps as current regulators is one, linearization with just one perfectly calculated inductance, snubber caps and diodes, or components wired in an usual way to perform two or three functions at once are other examples. And for their trickery and dearth of means, these circuits work really well!
CuriousMarc Well, I guess CRT-based displays were around for, what, 70 years or so? From the ‘30s to the 2000s, right? So they did have plenty of time to refine their circuits and learn what worked and what didn’t, while spending as little as possible. The more I go back and look at the stuff that was available back in the “analog” days, the more I’m amazed at how well they accomplished what they needed to do back then.
3:18 - Engage Safety Squints...
BTW - the use of a light bulb reminds me of the typical Wien-Bridge Oscillator circuit where a light bulb is used to provide automatic gain control - acting as a sort of PTC thermistor.
... and Mother on speed dial. Contact! I have recently discovered AvE's hilarious channel and found out that I was mispronouncing nearly everything electronical. Will correct that in the next vidjeos.
If I heard your comment correctly at 5:18 , it also sounds like you discovered ElectroBoom's channel too :)
Yes, Ken told me about Electroboom. Who knew electrical tinkering could turn into stand up comedy. Only on UA-cam...
What about the horizontal alignment ?
someone practicing scales on that beautiful piano of yours.
from my experience (i used to work as an audio engineer) i always wait for the bang after the click of the ON switch. It usually took a second but then the Amplifier would just explode and then everything is quiet xD (we got batch of 10 or so bad ones from the factory, where the HUGE caps were in backwards)
28v bulb? Hmm alot of small air craft type stuff uses 28v. Could be work a look if your fix fails at some point
Yes, we got original spec bulbs now. I just did not want to wait...
Fantastic. Please keep it up.
It looks like the wrong newer model was better than getting the original because it probably has less hours.
The guy actually has a Dolphin.
I stay on receipt but then you must also send curious Marc
Hmm... another little lamp... There seems to be a pattern there
2:20 - What's the optical table in the background for?
Somebody making holograms, or other top secret stuffs? :p
btw, they are sissies for not wanting to power up the monitor. CRTs aren't that scary. hehe
Yes, holograms coming up. Preview video here: ua-cam.com/video/TnFdaIz7k0w/v-deo.html
CuriousMarc
Awesome.
I tried to sell my 70mW JDS Uniphase multi-line Argon laser / space heater a few times now, but they've all but been replaced by diodes now.
I'll check out the vid. Thanks.
Those are expensive lights!
And Curious Marc said "I am your Father"
Hahah I have the same or very similar VTVM!
606×808 pixels
Well, if it works when it's off then why can't you use it when it's off? Yes...... Let's try it!