Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
On screen display and other CRT items....
|
wshawlee2
The "ripple" in the on screen display function of the Tek 7K frames
was a deliberate thing. It was used to prevent phosphor burn by moving the display around slightly, enough to prevent phosphor burn, but hopefully not enough to be visually irritating. This problem becomes very complex in storage scopes, and there are several options to do this in different ways, plus many have the display deleted altogether to avoid the problem. Very late scopes have a different symbol generator card set, and the display does not move, plus the characters look a bit different. I am not sure if they got tired of service complaints about the wiggling display or what, but the "8"'s certainly looked better. The focus of this display function is tricky, as it is a brief time- multiplexed data item in the over-all horizontal sweep process. Its intensity is high to be visible (because the time is short), and this makes the gun dynamics different during this brief interval. This often means a subtle difference in focus or astigmatism occurs. Interestingly, if the data display is far out of focus, it invariably seems to be tied to a weak CRT, and is an early indicator it needs replacing. Tubes in this state also exhibit the odd "decreasing intensity" trait at very high intensity control settings. Many people leave their scopes on (at high intensity) all day. This is very foolish, as it consumes the one thing you can't easily replace in the scope, the CRT. Many HP network analyzer guys did the same thing, and there are now hundreds of them running around trying to get replacement CRTs, which simply don't exist. Their $20K analyzers are now dimly lit doorstops. There is a way to work around this situation, but it's not simple. Good practice is to keep intensity low, and the scope/analyzer off when not in use. A surge protected power bar is an excellent idea, as the switching regulators had no real over-voltage protection until very late in the 22xx series production. A $25 accessory can save your scope from total death. all for now, walter |
|
Oh, Walter,
toggle quoted message
Show quoted text
I have a bone to pick with you over some things that you said. But before that, let me tell you that it never occurred to me that this wiggling of display was done deliberately to protect phosphor. I always found it annoying and thought it was some mis-adjustment, never guessed a real cause. No argument about keeping beam intensity as low as needed and off when not using scope, but turning scope off and on several times a day is not the very best of ideas. Personally, I would turn off scope only when it was unlikely to be used for several days; there have always been exceptions, like company fire regulations and freaked out bosses, that made mandatory turn off before going home, but given choice, I stuck to my habit. Let's face it, even well designed equipment experiences most stress at turning on/off. For (working) tube scopes (and all CRTs) turning off seems quite logical, considering cathode emissivity degradation over time. However, turn on filament current inrush and thermal shock kill more tubes than old age (loss of emissivity). I understand that tube computers used to have a gradual application of filament voltage, in order to keep tube mortality low, and still the machines were kept on at all times except when maintenance required differently. An attempt to preserve emissivity by turning off plate voltage, led to discovery of 'sleeping sickness', an effect that a seemingly good cathode looses emissivity if it was heated to rated temperature for an extended period of time without current, i.e. plate voltage applied; I believe that 'extended period of time' also means an accumulation of multiple minutes without voltage, not only stretches of hours. In another scheme to extend tube's life, the cathode is heated just to a glow, not to full temperature. In that way turn on shock from cold cathode is greatly reduced and emissivity is for most part preserved, without 'sleeping sickness', plate voltage applied or not. This mode is a kind of a standby that is widely used in TV receivers for CRTs. I thought that there was a standby mode for 551 (2 box, dual beam job), but picture in Stan's book does not show a switch for standby mode. Anyone remembers standby switch on a Tektronix scope and what does it really do? As for 'surge protected power bar', in principle that is very good idea, but you must consider reality of it. All commercially available surge protectors, that I have seen, use MOVs (metal oxide varistor). The UL requires that a certain surge profile (so many volts for so many milliseconds) is applied to DUT (surge protector, office appliance etc.) and the result must not be flying shrapnel or flames. The surge protectors usually available at Ace Hardware and 'Computor Stores' use a quarter (coin) sized MOVs. Such a small MOV can not absorb much energy and its voltage tolerance is rather wide, so they are sized to fire around 375Vac, nominal, where spikes are narrow and do not overstress MOV; the equipment is yours, so that is your problem. Using those 375 Vac MOVs keeps manufacturer of 'protection bar' out of UL hot waters, even without fusing that would not break under load but disconnect before fire becomes steady. The better surge protectors use 1 ???" diameter sized MOVs, free standing or packaged in plastic housing, and always have an adequate fuse or circuit breaker. Besides better energy absorption, those bigger and more expensive MOVs also have narrower firing voltage tolerances. As an example, looking at 1995 Harris data book (nee GE, nowadays I do not know), a 130 V device in quarter sized form (largest LA series) has firing voltage range 184 to 255 Vdc, corresponding to 130 to 180 Vrms, while bigger device from HA series has a range from 184 to 228 Vdc (130 to 160 Vrms); bigger devices cost more so manufacturer can absorb a bigger yield hit. Then, after firing point, as current rises so does voltage across 'crow bar', much steeper across a smaller device than the bigger one. Now, the protection takes an additional hit, on top of the tolerance based one. Using HA series devices does not give you anything to brag about, but small device is dis-proportionally worse. The tolerance spread and low energy absorption found in a small device makes a 130 V rated devices impossible to use, so you are pushed to higher rating, like 375 Vrms, what renders the whole surge protection to a farce. This discussion based on GE devices is valid across the board or it is a better case, since all Japanese and Taiwanese made devices, that I have seen, have same form factor, though the color is different. The presumption is that those are knock offs of GE devices, possibly with wider tolerances. Semiconductor based clamps, pure brute force zeners or integrated zener and SCR, have very much better characteristics, but I have not seen them used in a power strip. Your statement that there was no surge protection before 2400 series made me go and look in the manual. Yes and No. I want have you bad mouth my 7904, there are gas filled surge absorbers across both legs of rectifier, so your statement is a slander. I could not see the size of tubes, but very small packages can absorb high energy; telephone companies love them for premises entry protection. The manual for serial numbers 260K and up, shows those tubes as DS1208 and DS1213, 230 V rated, listed as Tek supplied, most likely selected for voltage. The fact that leaves me uneasy is that electrolytics after input rectifier are rated 200 V (working, and surge is probably no more than 250 V). Several months ago someone on this forum lamented that Tek used caps rated on the knife edge and I am sorry that I can not disagree with that statement. As an aside, I checked 7603, too. There are no surge suppressors there, but at least electrolytics are rated more generously, e.g. 53 V nominal (58 V at high line) uses 75 V working rating cap. Those are points that I wanted to dispute. Regards Miroslav Pokorni ----- Original Message -----
From: "wshawlee2" <walter2@...> To: <TekScopes@...> Sent: Friday, January 18, 2002 4:26 PM Subject: [TekScopes] On screen display and other CRT items.... The "ripple" in the on screen display function of the Tek 7K frames |
|
Stan or Patricia Griffiths
The only two Tek scopes that I can remember having more than one power switch
are the 507 and 517 and I don't really recall what the real story was on those. I think they were separate switches for filament and DC power. I don't recall anything like a "standby switch". One other reason you might not want to keep your scope turned on all of the time is that tubes in distributed amplifiers develop cathode interface over long hours of on time. The only answer to cathode interface is to retube the amplifier. In order the "save the CRT" it has also been suggested to simply turn down the intensity to cut off the CRT beam current. In the case of some of the 560 series, I understand that even if there is no visible display on screen, the CRT cathode may be emitting anyway. This is because some scopes used a scheme of driving the beam off screen during retrace time so it was not visible, rather than actually shutting down the CRT gun. I can't be more specific about model numbers because this is all from my weak, 63 year old, memory . . . I also recall, vaguely, something about some adjustments in some 7K mainframes to minimize things like readout jitter due to thermal heating of the vertical position stages when the vertical has to make large and rapid changes in beam position due to going from displaying readouts on screen to switching way off screen to a trace way above or way below the screen. This is another "weak" memory of mine. Maybe Dean has more on this . . . Stan w7ni@... |
|
The company I work for has sold custom flat panel displays to another major
US test equipment manufacturer (use your imagination here). About 5 years ago, their info said their analog scope CRT life historically was between 40-80K hours typical. This discussion was in the context of concern regarding CFL backlight life of AMLCD flat panel displays, which was about 10K hours back then (to 50% of initial brightness). They did not want to get in a situation of having to replace backlights mulitiple times during the life of the instrument, when this wasn't an expectation for the analog CRTs, but I digress. Assuming Tek tube life is similar to the stated CRT life mentioned above, one would burn up a tube in roughly 4 to 8 years if the instrument was left on all the time. For that reason, plus the benefit of saving power (something not all that abundant as was shown this last summer) and life of other parts like electrolytic caps, I tend to shut everything off when not in use, or when I won't be back to it for more than a couple hours. I've had a 2465A at work for 13 years now, and even when it's on, if I'm not using it for a short bit, I will put the scope in single shot mode to shutoff the beam and readout. It still has a very healthy CRT despite starting life as a rental instrument. Hopefully, when used only when needed, the instrument will last a lifetime :>) My Heathkit 25" TV, with brightness and contrast used in moderation, has lasted so far 19 years. Perhaps too long according to my wife.... Don |
I also recall, vaguely, something about some adjustments in some 7K mainframesUnfortunately, the IC vertical designs don't have a thermal compensation adjustment. Again, the 7904 is an example, and my 7904s do suffer from swimming readouts. |
|
Don,
toggle quoted message
Show quoted text
I like single shot mode for scope standby, too. A number of times I forgot that scope was in single shot and spent some time trying to find out 'what is wrong with my scope', but I still think that is a better way, because you do not have to mess up any settings. It did surprise me that life of a CRT was in the range of 40 k to 80 k hours; my gut feel was that it was around 10 k. I never had a CRT to die on me, it was only passives, mostly electrolytics. While I was still working with tube scopes never had any tube to die on me, though that was a matter of luck, and at that company there was security guard who would come around and turn everything off and write you up even for soldering iron that was left on. When I was talking about keeping a scope on all the time, I did say 'working ' (as opposed to scope from collection used for hobby work). When paid to do work one should not spend too much time trying to save pennies and skip over dollars. Regards Miroslav Pokorni ----- Original Message -----
From: <donlcramer@...> To: <TekScopes@...> Sent: Monday, January 21, 2002 9:48 PM Subject: Re: [TekScopes] On screen display and other CRT items.... The company I work for has sold custom flat panel displays to anothermajor US test equipment manufacturer (use your imagination here). About 5 yearsget in a situation of having to replace backlights mulitiple times during theCRTs, but I digress.one would burn up a tube in roughly 4 to 8 years if the instrument was left on(something not all that abundant as was shown this last summer) and life of otherparts like electrolytic caps, I tend to shut everything off when not in use, orat work for 13 years now, and even when it's on, if I'm not using it for ashort bit, I will put the scope in single shot mode to shutoff the beam andrental instrument. Hopefully, when used only when needed, the instrument willlast a lifetime :>) |
|
I was initially surprised by the 40-80Kh number also. The difference I think
is that in a scope the tube is not driven as often (duty factor) or as hard (especially white background applications) as a CRT is in a raster scan application. Therefore I would expect digital scopes using raster CRT displays to have shorter lives than analog scopes or, say, 2400 series digital scopes which vector write an analog scope type CRT. In CRT raster scan applications, I would agree with 10Kh though they seem to last a lot longer now than 10-15 years ago. Remember those old 12" monochrome CRT monitors for PC use in the early 1980's (e.g. for HP80 series desktop computers)? If we left those greenscreens on 24/7 on our burn-in systems, they'd be toast in a year. After the first wave had to be replaced, the production operators would turn them down at night before they went home, and left them down whenever they did not have to see the display. In later years (the systems ran 17 years I'm proud to say), we couldn't even find replacement "NTSC sorta" analog input monitors. And how about those EGA color displays from around 1990?--tubes went fuzzy fast with Windows applications. We had a whole room of the things with bad tubes (and also broken electronics). Of course it didn't help that people ran, ahem, "screen saver" pictures on them when not in use. If the scope CRT number is truly closer to 10Kh there would be a lot more junk scopes around our operation, as most are left on in production, through two shifts, 5+ days a week, in auto sweep mode (with the brightness turned up too high to boot). To the best of my knowledge, we've never pulled a CRT in any of the scopes, and most of those go back more than 10 years (including a couple Tek 465Bs, Leader 100Mhz dual trace, a couple Tek 2200 series). Any more we would junk them for whatever cause if they failed--I have two I got that way. One (465B) I restored and the other (TAS465) I haven't found a service manual for yet. Both have good CRTs though. The only dim scope tube is in our trusty 571 (bought from Tucker many moons ago) which exhibits the double peaking on the intensity control that others have mentioned. The trace is pretty dim when cold, though improves with a good warmup. I watch it closely to make sure nobody just leaves it running. Quite frankly, I don't think there is anyone left besides me that can run it anyway so it is in a way "out to pasture". I've wondered if a replacement CRT is available for them from anybody.... Don |
|
John Miles
On this topic, does anyone know how to disable the "screen saver" feature
toggle quoted message
Show quoted text
that blanks the 2467's BrightEye CRT after about 3 seconds? (exaggerating for effect, but sometimes it almost seems that quick.) It's very annoying, not to mention dangerous, to manuever a probe into a delicate, cramped position and have your scope go into "shutdown" mode just as you're about to read it. Why in the world didn't they make the screen-saver timer reset itself at each incoming trigger event? What was Tek thinking? -- jm ----- Original Message -----
From: "Miroslav Pokorni" <mpokorni2000@...> To: <TekScopes@...> Sent: Tuesday, January 22, 2002 3:23 PM Subject: Re: [TekScopes] On screen display and other CRT items.... Don,you do not have to mess up any settings. |
|
Dear John,
toggle quoted message
Show quoted text
I think that overriding concern was preserving MCP, which even overshadowed concern for phosphor. It appears that brightness setting is significant factor in time out. I seem to remember reading that shutdown is forced after so many Coulombs (ampere-seconds) of beam. The whole scope is processor controlled, so it might be pretty tough to fool it. A possibility is to fudge beam current sense, but that might effect intensity setting control and certainly would jeopardize MCP. It makes me dizzy to even think of the price of replacement CRT for that scope. It seems to me that better way would be to learn what parameters effect time out and work with it or around it. In years that I worked with one of those there were times when it did just fine and than it would get temperamental (or it was me who would forget to set it right). Fact is, I never spent time to find out what is right setting, I just kept pushing this Beam Finding button, to reset time out. However, if you find a way, please let me know. I have one and do not have manual yet and I guess I do not have guts to attack that shutdown, though it annoyed me almost to the limit of my patience. Regards Miroslav Pokorni ----- Original Message -----
From: "John Miles" <jmiles@...> To: <TekScopes@...> Sent: Tuesday, January 22, 2002 8:30 PM Subject: Re: [TekScopes] On screen display and other CRT items.... On this topic, does anyone know how to disable the "screen saver" featurejust as you're about to read it. Why in the world didn't they make theforgot 'whatthat scope was in single shot and spent some time trying to find out is wrong with my scope', but I still think that is a better way, becauseyoudo not have to mess up any settings. |
|
Dear Don,
toggle quoted message
Show quoted text
I assumed that 40 k to 80 k applied to scope CRTs, not raster driven. Somehow, and possibly wrongly, I assume that scope CRT is made more durable than raster one, if for no other reason then for size and price expectations. The scope CRT does have more glass penetration points (a draw back), but glass envelope can be made thicker considering the size of the whole device. I plucked 10 k number from life of 'Long Life Tubes', you know, E800F as opposed to standard EF800, though somewhat longer life would be expected when you shell out few thousand bucks for a tube. It surprised me when Walter said that he found lot of 'gassy' tubes. I always associated that with TV CRTs (I view TV as something at par with PC in cheapness). Walter, was gassing perhaps coming from pin abuse (bent pins close to glass)? The PC monitors should not be brought into this comparison; in olden days they were the cheapest thing that could be found and I do not think that much has changed. To give you an idea about attitudes in PC industry (and some laughs or concerns perhaps), let me digress. Few years ago I went to a seminar on switch mode power supplies, given by Linear Technology. Apparently, switch mode ICs are competitive commodity and Linear Tech is trying to sell theirs as a 'cut above'. Their head application guy, Jim Williams, usually says: 'before we had switch mode ICs we were telling customers not to use switch mode power supplies (SMPS) because of noise and now we say that is the only thing'. During lunch I set at the table with one of SMPS application guys and he was telling about trip to Taiwan. They were at a mother board supplier (name withheld) and Linear Tech guy pointed that with low value inductor (hence cheap) ripple current was killing electrolytics. Taiwanese guy asked 'what is the problem when warranty on product is 30 days'. In contrast to junky PCs, I had a VT220 terminal for 10 years. Intensity was turned up as high as it would go, to be able to read screen in office light. The monitor was opened up ones to increase maximum intensity limit and it still lives; the terminal operated in 24/7 regime. It is true that VT220 shuts down CRT after no key strokes or input data for ??? an hour. But, company also had a half a dozen of monitors hung on test systems, which were getting periodic input from computer at intervals from 15 minutes to couple of hours, so they were driven hard. I do not think that any CRT failed, though there were few failures. I did not let terminals be repaired (I could buy replacement for under $50), but few, that technicians sneaked by, never turned up bad CRT. Funny that you mention high intensity in auto sweep mode. It looks like all test technicians love that; and they are usually young, with good eyes. The furthest that I got with that problem was that technicians would sometime turn down brightness when I walk into test department. At place where I worked, I know that technicians did not understand concept of synchronizing signal and probably upped brightness to be able to see something in trace as it flies by. Their use of scope has always been a mystery to me: how do you know what you are looking at with only one probe and no external trigger? What is 571? I could not find it in Stan's book, neither in 1995 Tucker catalog. Regards Miroslav Pokorni ----- Original Message -----
From: <donlcramer@...> To: <TekScopes@...> Sent: Tuesday, January 22, 2002 11:22 PM Subject: Re: [TekScopes] On screen display and other CRT items.... I was initially surprised by the 40-80Kh number also. The difference Ithink is that in a scope the tube is not driven as often (duty factor) or ashard (especially white background applications) as a CRT is in a raster scanto last a lot longer now than 10-15 years ago. Remember those old 12"series desktop computers)? If we left those greenscreens on 24/7 on our burn-inreplaced, the production operators would turn them down at night before they wenthome, and left them down whenever they did not have to see the display. Inlater years (the systems ran 17 years I'm proud to say), we couldn't even find"screen saver" pictures on them when not in use.through two shifts, 5+ days a week, in auto sweep mode (with the brightness turnedup too high to boot). To the best of my knowledge, we've never pulled a CRTin any of the scopes, and most of those go back more than 10 years (includinga couple Tek 465Bs, Leader 100Mhz dual trace, a couple Tek 2200 series).Any more we would junk them for whatever cause if they failed--I have two Igot that way. One (465B) I restored and the other (TAS465) I haven't found amoons ago) which exhibits the double peaking on the intensity control thatothers have mentioned. The trace is pretty dim when cold, though improves with arunning. Quite frankly, I don't think there is anyone left besides me that can runit anyway so it is in a way "out to pasture". I've wondered if a replacement |
From: donlcramer@... [mailto:donlcramer@...]I'm coming in late, so pardon if I'm responding to a non-issue. Someone doesn't recognize the 571. That was Tek's first transistor curve tracer. Looks similar to its predecessor the 570 tube curve tracer. I used one in school, great instrument but superseded by the 576 (smaller, looks more 7000-ish, claims to do FETs as well as bipolars*) and I don't know what-all since then. * You can sort of do FETs on the 571 too, but it won't tell you how. Regards, Dave Wise |
|
Craig Sawyers
I'm coming in late, so pardon if I'm respondingI think you're thinking of the 575, David. I have one just behind me as I type. They do Tunnel Diodes too (with care), and mine will in due course do tubes as well (via an add-on box fed from the 175 connector on the back and the tranny sockets on the front). The only limitation for tubes is the 200V maximum collector (anode) sweep. Those lucky ones who have an option (I think 21?) have a 400V sweep, and that would clearly be even more useful. Craig |
From: Craig Sawyers [mailto:c.sawyers@...]Shoot, you're absolutely right. I was only off by one bit,I'm coming in late, so pardon if I'm respondingI think you're thinking of the 575, David. I have one just TMSAISTI. :-) Dave Wise |
|
Stan or Patricia Griffiths
Hi David,
toggle quoted message
Show quoted text
I think you are thinking of the 575, not 571. I don't think Tek ever assigned 571 to any instrument. Stan w7ni@... David Wise wrote: From: donlcramer@... [mailto:donlcramer@...]I'm coming in late, so pardon if I'm responding |
|
Stan or Patricia Griffiths
Hi Craig,
toggle quoted message
Show quoted text
The 575 option you are thinking of is called "Mod 122C". I have one. Stan w7ni@... Craig Sawyers wrote: I'm coming in late, so pardon if I'm respondingI think you're thinking of the 575, David. I have one just behind me as I |
|
Craig Sawyers
Hi Stan
The 575 option you are thinking of is called "Mod 122C".I *thought* it had a 2 and a 1 in it somewhere! I have one.That comes as no surprise whatever ;-) On another topic, I was picking up a piece of AVO test gear this morning for a guy I know quite well, and we were talking about 570's. Apparently a friend of his picked one up at a hamfest in October for (wait for it...) ?10!!!!! The guy selling it clearly didn't know what it was, or its rarity. Although I too got a mini bargain today on eBay - the capacitance standardizers for the 500 series scope plug ins - for $5 each. Cheers Craig |
|
I have never heard of 571. But, Dave, I take exception to your leap to 576.
toggle quoted message
Show quoted text
As a proud owner of a 575 I can not let it go by that you skip mentioning the old transistor tracer stalwart. Regards Miroslav Pokorni ----- Original Message -----
From: "David Wise" <david_wise@...> To: <TekScopes@...> Sent: Thursday, January 24, 2002 10:34 AM Subject: RE: [TekScopes] On screen display and other CRT items.... From: donlcramer@... [mailto:donlcramer@...]I'm coming in late, so pardon if I'm responding |
|
Craig,
toggle quoted message
Show quoted text
The option is 122C and Tek calls it 'High Voltage Diode Check'. I do not have that option on my 575 but I infer from manual that current capability is less than 1 mA: manual recommends to set display current to 0.01mA/div when using this option. If you really want to convert your 575, I have a write up, but work appears quite messy. The major additions are a transformer and sections to rotary switches and there are also some changes to wiring. Regards Miroslav Pokorni ----- Original Message -----
From: "Craig Sawyers" <c.sawyers@...> To: <TekScopes@...> Sent: Thursday, January 24, 2002 11:00 AM Subject: RE: [TekScopes] On screen display and other CRT items.... doI'm coming in late, so pardon if I'm respondingI think you're thinking of the 575, David. I have one just behind me as I tubes as well (via an add-on box fed from the 175 connector on the backand the tranny sockets on the front). The only limitation for tubes is the200V maximum collector (anode) sweep. Those lucky ones who have an option (I |
From: Miroslav Pokorni [mailto:mpokorni2000@...]I was confused about the model number, Miroslav. In my post below, I say "571" but I really mean "575". And I wouldn't in the least mind having one. I would only mind having to ship it :-) Since that post, someone noted that there really is a Tek 571, but I've never seen or heard of it before. Regards, Dave Wise From: "David Wise" <david_wise@...> |
to navigate to use esc to dismiss