In article <009c01c72a37$59814380$6600a8c0 at HPLAPTOP>, "Jay West" <jwest at classiccmp.org> writes: Cool! Is this a Dasher? -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download <http://www.xmission.com/~legalize/book/download/index.html> Legalize Adulthood! <http://blogs.xmission.com/legalize/>

Alexandre Souza wrote: At least in the case of the HP250 one, the aspect ratio of the CRT is around 2:1 (unlike most screens which are closer to 4:3). I'm surprised if HP got a CRT custom-built just for them, but maybe that was the case; certainly I've seen nothing like it in any other displays ever. Mac portrait displays are presumably similarly difficult to get replacement CRTs for, at least without realigning the yoke (I gather that most CRTs don't like a change in orientation, although I used to run a Sun colour display on its side a few years ago with no obvious ill-effects) For more conventional equipment I suspect that a swap is possible, providing knowledge of how to tweak the old circuits with the new tube is known. cheers Jules

I wouldn't be suprised if it was a custom CRT. Rememebr HP made a lot of 'scopes over the years, and some of those had specially-designed CRTs (admittedly electorstatically deflected). And the CRT in the HP9100 calculator (also electrostatically deflected) is a custom job, it has a much larger deflection angle than most electrostatic CRTs. For that matter look at the HP87. That CRT has a very odd aspect ration (think of it as being a normal CRT 'cut in half horizontally'. Never seen anything else like it. Do colour portrait displays exist? The reason I ask is that I wonder if they use specially designed CRTs. IIRC, the whole point of the 'in line gun' (PIL) CRT was that the 3 electron gus were in a horizontal line, so that only the vertical component of the earth's magnetic field had much effect on the convergence, and that was relatively constant in a given area. So if the CRT was set up properly you could move the unit around without having to do a reconvergence (this was a problem with delta-gun CRTs which had to be set up in the positionan nnd orientation where they were going to be used, but if that was done they give an excellent picture). Anyway, for a portait disply you would hope the CRT had the 3 guns aligned along a like parallel to the 'short' side of the CRT. But that would be a custom CRT. For mono CRTs there's no problem, of course, and at least some portrait displays use a normal CRT mounted 'sideways' If you're doing a CRT swap, keep the yoke with the electronics (PCB, etc), not the CRT. Yokes are a lot less generic than CRTs. So the issue of hacing to realign the yoke (trivial on a monochrome unit) is moot anyway. -tony

I had written.... I humbly apologize for my misstatement. It's not Steve's site apparently, which talks about removing and replacing the entire crt. Another listmember I guess... had a website showing a jig he built to hold the monitor and described cutting the safety glass off with a nichrome wire. I can't seem to find that site at the moment. Anyone recall what it is? Jay West

Jay West wrote: Hmm... I found that the CRT was heavy enough not to move around anyway; I just put the CRT on its side (so I was cutting through the shorter edge) and cut worried about the localised heat damaging the tube. I just used a surplus PC PSU and a stray bit of resistance wire, but the short edge of the HP's screen was only 8" maybe; something with a bit more kick would have been needed for a more conventional tube. Afraid not - just looking at my archives now and I don't see anyone mentioning a site when I was talking with other listmembers about the HP above. Steve Loboyko, Dave Brown (both HP) and Bob Shannon (Imlac) appear to be the only others who had tried doing this at that point in time. cheers Jules

In article <6.1.2.0.2.20061227235750.0a125150 at mail.marcal.com>, Dan Veeneman <dan at decodesystems.com> writes: But isn't that talking about replacing the whole tube, not removing the faceplate to clean off the mold? -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download <http://www.xmission.com/~legalize/book/download/index.html> Legalize Adulthood! <http://blogs.xmission.com/legalize/>

Jules Richardson wrote: You probably want to talk to a windscreen specialist. They make funny bits of curved laminated glass all the time. Gordon

Jules Richardson wrote: It goes like that around cracks, too - it's something to do with water getting in I think. Oh, and never mind 70s, my 1991 Citro?n XM is getting like that. I've seen cars less than five years old with the same problem, so I suppose it's yet another of these "newer is crappier" things. Gordon

Chuck Guzis wrote: Well translucent caulk was what I used for the HP screen, and at those thicknesses it seemed to do the job well; the problem was just that the stuff isn't dilute enough to pour, and spreading it over the surfaces before pressing together would likely trap air bubbles in there which would be highly visible. Diluting it with *something* would probably work, but I'm no chemist so I'm not sure what would dilute it and still allow it to dry over a longer period (and not contract significantly in the process when it dries, or prove a fire hazard or whatever :-) More testing needed... cheers Jules

The power supply is a very simple transformer/regulator linear supply. It is described in section 4.3.18 on page 4-21 of the ADM3A Maintenance Manual, which is page 37 of my PDF. The full schematic of the supply is located near the end in drawing #129471 which is page 103 of my PDF. Are you sure the terminal is completely power-dead, and not just "not working" - Measure the power rails of the logic ICs and also look for the filiment glow from the CRT - these indicate the 5v and 12v supplies (respectively) are working. Assuming it is power supply: I'd begin by disconnecting P3 and P4 and measuring the output of the transformer windings and confirm that they are close to the values listed on the Schematic. If no voltage on any windings, check the fuse, switch and associated wiring between the mains and the transformer. A good fast check is to measure resistance across the AC mains plug (not plugged in of course) - it should read infinite with the switch OFF and very low with the switch ON . If voltages are present but low in all or some windings, check the connections to/from the transformer. If only one output is affected and connections are good, the transformer may be shorted or open. Powering through 40w light bulb may reveal shorted windings - with P3/P4 disconnected the Xfmr should draw almost no current - if the light bulb glows there may be a hort. Open windings can be checked in non-powered state with an Ohm-meter. If AC voltages are OK, I would reconnect P3/P4 and check the outputs of the full wave bridge rectifiers - they should be at least 2V above the rated output of the connected regulators (and will probably be higher). You can check them at the bridges, or at the input side of the regulators. If voltages are low, rectifier may be bad, or you may have a shorted regulator. A scope can be handy here as examing the shape of the signal input to the regulator it will let you see if one leg of the rectifier is shorted/open. If inputs to the regulators are OK, check the outputs - these should be very close (ie: almost exactly) the rated output voltages of the regulators. If too high, you have a bad regulator (and may have damaged other components). If too low, either the regulator is bad or the circuitry beyond it is drawing too much current and causing it to shut down. A thermal probe can be very handy, most of this stuff heats up if there is excessive current draw. Once you are well away from the mains, fingers can be used, but be warned that things can get *VERY* hot, enough to cause burns. Your nose and ears are also good tools, as "hot smells" and "sizzling sounds" are things you should pay attention to. Powering the terminal though a high wattage (100w or more) light bulb can minimize damage if components are shorted - the bulb lights and acts as a current limiter. If the bulb remains glowing brightly after the terminal is switched on, power it off and find the cause of the excessive current draw. WEAR EYE PROTECTION WHEN WORKING ON POWER SUPPLIES! I've had shorted regulators explode with enough force to penetrate a wall beside my workbench. Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html

Was that a nuclear power supply??? :oO :oD

On Wed, 27 Dec 2006, Doc Shipley wrote: and "The Pepsi Syndrome"

In article <03df01c729e3$90322970$f0fea8c0 at alpha>, "Alexandre Souza" <alexandre-listas at e-secure.com.br> writes: Are you saying that "phosphor screen burn" on a CRT can be fixed by a strong exposure to sunlight? -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download <http://www.xmission.com/~legalize/book/download/index.html> Legalize Adulthood! <http://blogs.xmission.com/legalize/>

At 10:31 AM -0700 12/27/06, Richard wrote: That sounds too bizarre - I would expect that strong exposure to the sun would simply fade the phosphors even more... John :-#)# (thinking of sticking some monitors out back to test - can't hurt!)

On 27 Dec 2006 at 15:23, Chris M wrote: In the "good old days", that's how TV CRT's would be recycled. Just a new gun assembly and you're off and running. Of course, nowadays we just toss 'em into a toxic landfill. Cheers, Chuck

Chris M wrote: In the old days, the primary problem was loss of cathode emission. Cathodes are made with a special coating (lovely stuff like barium-calcium-strontium carbonates *) or alloy to get the electrons to fly off more readily. Significant improvements in that area were made over the years, so it may be that phosphor-light-emission loss occurs before cathode-electron-emission loss these days. The other trick in the old days was the picture tube booster, a small autotransformer plugged in between the chassis connector and the CRT to boost the filament voltage and run the cathode hotter. After the CRT deteriorated further you might have it re-gunned. (* If you look at the range of stuff that goes into a vacuum tube it's quite a tour of the periodic table.)

--- Brent Hilpert <hilpert at cs.ubc.ca> wrote: I obtained a brand new one of these, probably specific to a particular make/model, but don't ask me which (it ain't in front of me). I had also heard that there's something called an "age switch", but I have to wonder if the guy was pulling my leg, cuz I never found one. But possibly it employed a technique like this? __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

Chris M wrote: Certain old TVs had a separate CRT heater supply that could be adjusted up and down a bit. Also, one I remember (BRC 1400 chassis? Dead common around here, whatever it was) had a resistor across the heater, to act as a shunt. Thus the heater was actually rated for 150mA instead of the 300mA of the rest of the heater string, and you could drop out a link on the shunt resistor to put a bit more through the heater. Bodgetastic stuff. Oh, and of course there was the big tapped wirewound with voltages printed on for anything from about 200v up to 260v - mains could be very variable out in the sticks. Gordon

No, in general the phosphors were fine, it was the cathode emission that failed (or in rare cases the heater burnt out). So replacing the gun would bring an old tube back to life. There were a couple of tricks that were tried to extend the life of failing CRTs. One was to over-run the heater somewhat. In a series-string heater TV, the CRT was almost always at the shassis end of the string, with one terminal connected to the chassis. A suitable resistor from a 'live' point on the mains dropping resistor to the other terminal of the CRT heater would do that. If there was a shunt resistor across the heater, removing it (or increasing the value) helped. If the CRT heater was fed froma low-voltage sourve (secondary of a power transformer or the flyback transoformer), there was often a series resistor you could short out. The other trick was to over-run the CRT filament on the bench (give it as much voltage as you dared -- 10V for a 6.3V heater was not uncommon) and apply a few hundred volts DC between the cathode and the first (control) grid. The indea was to have a strong electric field at the surface of the cathode which would tend to 'strip off' the top layer of the cathode, exposing fresh emissive material. Both tricks were a 'last resort' THer was the risk of burning out the heater, and in the case of the second trick of stripping the cathode totally (so no emission at all). And they tend to work better on older CRTs (modern ones have a much thinner emissive layer, or so I am told). None-the-less, I managed to use the second trick to get a bit more life out of a Mac+ CRT... -tony

AFAIK, there is no way to 'clean' burn off a CRT. The burn you see is discoloration and deterioration of the phosphors themselves, and you're not going to "bring them back" by exposing them to the sunlight. I could imagine that you could theoretically discolor the rest of the tube to look similar though. If there was sun this time of year, I'd set a burnt out tube outside and cover one half with cardboard, see if the sun is capable of discoloring or changing the appearance of the phosphor at all. As far as a dim tube, you can kinda brighten a weak tube by boosting the filament voltage a bit. Don't go too high, or you'll burn out the filament. CRT boosters for TV sets were common in the 50's and 60's. They worked, but not for all that long. The only solution then is a rebuilt or replacement tube. Mold behind the CRT face is pretty common on old TV sets. In particular, the old round 21" color tubes develop "cataracts" caused by the PVA compound located between the safety glass and the tube face deteriorating and molding. To clean this, on these tubes anyway, you remove the faceplate. To do this without cracking it, remove the tube and set it neck down in a container that will hold it (bucket or somesuch). Heat the face of the tube with a heat gun. Heat evenly and try to get bubbles to form in the PVA compound. Once you've gotten bubbles to form, you want to work toward the edge of the tube, and try to free the safety glass from the rest of the tube, lever gently with a popsicle stick or something. This works at least on the TV tubes that have a safety _glass_. I think sometimes the face on terminals is plastic. Might want to stick with low heat. Once the glass is off, you should be able to peel away the PVA coating some chemical cleaner like paint stripper. This works on the TV tubes, I have never seen it done on a terminal tube, but if they were made the same way I'd say it is worth a shot. Maybe start with a hair dryer and see if you can get the PVA to bubble or soften. I know the Zenith TV tubes had a different sort of PVA, and those didn't work with this method. I think people were cutting the faceplates off with nichrome wire. When picture tubes are rebuilt, the guns are cut off and new ones are attached. For color tubes, the phosphors are not replaced, and only tubes without screen burn are rebuilt at all. For black and white tubes, it is possible to replace the phosphors, and this was common back in the 50's. In general though, a big cause of lack of brightness is simply a deteriorated filament/cathode. Early black and white tubes (pre aluminized screen) had a phosphor that discolored much more easily, to the point that the stray electron emission from the gun would eat a mark in the center of the tube. These tubes used ion traps to prevent this, and when rebuilt, new phosphors were the norm. For the vintage computer collector though, replacing picture tubes is generally done with used tubes from something else. A lot of monochrome tubes are pretty much interchangeable. Save junk terminals with decent tubes, they might come in handy. Also, don't overlook TV's - the picture tubes in 12" black and white TV's make a pretty good replacement for many computers, I've used a TV tube in a TRS-80 Model III. Also, one time when I was bored, I transplanted the tube from an IBM 5151 display into a 12" Zenith black and white TV set. It worked fine, although the long persistance phosphor and WordPerfect screen burn made TV unusual. The things to look out for in swapping tubes is the physical mounting, the neck size, and base. Typically, if the base matches up, the yoke fits and you can bolt it in there, it should work. Modifying mountings is OK and necessary sometimes, but NEVER CUT THE RIMBAND OFF A TUBE. That rimband is sometimes part of the mounting ears, and it is there as a critical structural component. It typically looks like a metal pallet strap. If removed, the implosion protection for the tube will be compromized, and the tube may very well implode/explode. I've heard horror stories about this. -Ian

Sounds bizarre to me too, but it works... :oO

Hi Fred I suspect that you are right. Still, without having a light meter handy we'd just be guessing. One of my terminals someplace has a mild burn on it from some menu. Next time I see it, I'll place it in the sun but mask of a section with foil. If it is just making things uniformly dim, the covered section will be brighter. Even so, it might better to get a uniform dimming than some burn letters. I have an old oscilloscope that has a hard burn. It looks like there is no phospher at all where the burn is. I doubt this could be recovered. Dwight _________________________________________________________________ Fixing up the home? Live Search can help http://imagine-windowslive.com/search/kits/default.aspx?kit=improve&loc…

On Wed, 2006-12-27 at 15:15 -0300, Alexandre Souza wrote: This is similar to the procedure I use. After the soaking, however, I run warmish tap water over it to remove any traces of soap. I then drizzle distilled water over it to remove the calcium in tap water, and give it a quick immersion in an alcohol bath. I do this, generally, for keyboards that separate. I don't like the picture of trying to dip an ADM-3. Slippery little buggers when soapy... Sorry, I can't buy this. Phosphor material is burnt OFF the glass by "burn-in," and no amount of sun will paint more on it. You must be talking about something else... Peace, Warren E. Wolfe wizard at voyager.net

DM-3. Slippery little buggers when soapy... Of course I did... And since I could not clean it enough with the toothbrush, i did soak the pcb and it is now drying. The unit is now dismantled, the case cleaned. A pity the transformer is not screwed on, but popped unto the base unit. While trying to remove the CRT shield I managed to crack it, so I will take the risk and use the now clean CRT without the shield. Since Richard asked : the case has a cream top and a brown base. The (3th party) graphic option is a Z80 based extra PCB that gives Tek-4014 emulation, but limited to 512x256 resolution. Google for "adm-3a rg-512" for more info. But I will first get the ADM to run before tackling the graphics option. Jos Dreesen

Me too, but it works. Maybe the sun burns the phospor more, dunno. But surely, it works.