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Re: Tek 7904 Display Problem
--- In TekScopes@y..., "Don Crano" <donc@s...> wrote:
Hi Alldisplay. to drift the display up and down, this is the trace/s and readouts as well.Note this is not on oscillation up and down. It will shift up for awhile,then drop down lower then it should be for awhile. I am talking about a 1/2CM or so. Everything is always on screen, it just gets annoying after awhile.readouts back on, and it will be fine again for a few hours or days.Hello Don, I had this problem. It turned out to be the channel switch hybrid U625 (part nr. 1555-0060). This is located on a 'mezzanine' PCB behind the two vertical plugins. Some other sources mentioned the two 1W metal film resistors on the vertical amplifier. hope this helps Patrick |
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Re: 465 Scan Expansion Mesh
John Rehwinkel
Yes, I put some of that mesh under a regular optical microscope hereI have a friend who has an electron microscope -- if anyone cares to lend me a bit of mesh, I'd be glad to get pictures of it and post them. Naturally, I'd return the mesh too if you like. -- John Rehwinkel KG4L spam@... |
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Re: 465 Scan Expansion Mesh
Stan,
Yeah, try to get most people to agree that the addition of the engine computer on a car was a step forward. I think the step forward was the fact that I have yet to not have a computerized car start within 2-3 seconds whether the temperature was -10°F or +110°F. The step backward is how, with so many vehicles being produced that (1) manufacturers over the world haven't settled on a common computer platform and (2) that to replace one costs as much as my full-blown home computer. I think the latter is simply because the manufacturers have us poor consumers by the kahoonies and know it. And back to the mesh vs. other methods. Not only can one compare meshless CRTs from the 1960's to the 465/475 and now to the digital scopes, but look at the digital scope displays. They're going to be limited not only because of the ±1 digit bobble, but because of the finite resolution of an LCD or a tri-color CRT dot pitch. No point in using ADCs with resolution better than the display resolution unless you have a method of "magnifying" the vertical and/or horizontal to take advantage of the increase ADC resolution. I've not looked up the LCD and color CRT specs to see where the two resolutions converge. Might be interesting! It's an issue not unlike having a 4-1/2 digit DMM display and only 0.5% accuracy on DCV and 1% accuracy on ACV. By the way, I had forgotten about the phosphor change. The P31 is more durable, that's for sure. I have seen a few P11's that were wrecked on 7904's and 485's that were being used for nuclear research out in Amarillo. They were always set up with a camera (obviously, with a P11) waiting for a single-shot event with the intensities cranked up to max. They were a BIG market for the 7104 in the OKC field office. And regarding nuclear research, I remember a field engineer telling me about selling a lot of transient digitizers to the nuclear research community. They'd put a TD down a hole with a bomb with the cabling leading to the blockhouse a couple of miles away. They'd blow up the bomb and the TD would send the signal out of all the stuff they were monitoring -- about 1?s before it went into total meltdown -- and then in the blockhouse monitoring station, they'd wait for the signal to show up and then after it was captured, high- speed clamps shut the lines down so the the massive EMP that was right on the tail of the data didn't totally destroy all the monitoring equipment. But the poor transient digitizers .... they got to make one and only one measurement in their entire lives before that serial number ceased to exist. Danged expensive probe! Dean |
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Re: 465 Scan Expansion Mesh
Stan or Patricia Griffiths
dhuster@... wrote:
And Stan, I don't know that I agree 100% about the mesh being a badHi Dean, It is great to hear other opinions and views on this sort of thing especially from someone who was as close to the situation as you have been. I suspect the difference in burned phosphors was due to the change from P2 to P31 for a standard phosphor in most general purpose scopes. Both of those phosphors look very much alike to the eye, being blue-green in color. I think that phoshor change took place about 1965 or so. Scopes shipped before that time with P2 phosphors where MUCH easier to burn . . . I don't think I have ever seen a CRT with a mesh and P2 at the same time . . . Yes, I put some of that mesh under a regular optical microscope here and found the same thing you did . . . it is etched rather than woven. I was surprised to discover that . . . Whether the fuzzy trace was a bad tradeoff or not is another one of those opinion issues. I just talked to one guy who told me he could see stuff (tiny wrinkles) in the trace of a 454 that just are not there in the display of the same signal on a 475, even though the 475 has 50 MHz more bandwidth and a much larger screen. The position I am coming from is that I was a Sales Engineer for Tek at the time mesh CRT's were introduced and I can tell you that MANY customers noticed the difference and were not pleased . . . they always expected the new model to be better, in every respect, than the one it replaced, sort of like cars. Well, they aren't always better in performance. Sometimes they are better in price, instead. Sort of like cars . . . Stan w7ni@... |
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Re: 465 Scan Expansion Mesh
I believe you're right, Stan. I'd heard both explanations.
Actually, the geometry story doesn't pan out well if you've ever seen one of the guns outside of the jug. the mesh is hemispherical in shape. If it dealt with geometry, I'd expect an odd shape to compensate for the extremes of the rectangular screen. For those who have never seen one, it is interesting. Very, very delicate, and so fine that when you hold it up to the light, it's like a diffraction grating, splitting the light up into different colors. It's also so fine that it will hold water. One little puff of air and you dimple it permanently. I send a piece of a mesh to friend Dale Johnson (used to work for Tek in the Dallas Service center, but at the time was working for a company that serviced scanning electron microscopes. He put the piece of mesh under a scope and the view was really interesting. It's quiet obvious that it's etched and not a woven screen that one first envisions. I don't know whatever happened to the Polaroid of that scan that I had. It should would make for an interesting post, but that was 25 years ago! Sometimes, during manufacturing, a little dirt gets inside the jug and finds its way to the mesh. The resulting display is a small spot on the CRT that just can't be illuminated by the beam because of the shadow effect it creates. I was rather irritated one time when a new 465B came in with that exact problem and the factory wasn't going to honor a warranty replacement of the jug because it was "still within all specifications of CRT anomolies". I put myself in the customer's shoes and decided that I wouldn't put up with a something like that in the windshield of a new car. Why should the customer put up with a manufacturing defectlike that in his $3500 scope? We replaced the CRT anyway and shoved the old one down factory's throat. Tek was starting to change from a very customer-oriented organization to a very money-conscious outfit. And Stan, I don't know that I agree 100% about the mesh being a bad deal compared to what the 535 had. I've never seen a burned CRT in a scope with a mesh and you can't say that about the old ones. The mesh diffused the beam enough that the CRT was pretty burn resistant. To me, the ±1 digit bobble of a digital scope is far worse to look at than the fuzzy trace of a 465. Dean |
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Re: Tek 7904 Display Problem
Don Crano
Hi Mark,
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Yeah I remember posting a list of the YaHoo groups I belong to. I know what you mean about the older scopes and their fine trace lines. My old 453 is still on of my favorites, I can sync it on anything I feed into it.<g> Under it sits a 475A with it's mixed mode delay is nice, but does not have the fine trace of the ol 453. On a Tekmobile 3 I have the 7904, with the two lower shelfs each holding a TM504A, and both fully loaded with plug-ins. So it is my mobile work bench, I can take it any where around the layout as need be.<g> I really do not have a count of the 7K and TM plug-ins I have and what works and does not work. But I am sure I do not have them all. Then on my bench I have a 2230 for what ever analog/digital I might need. Don Remember Always Have Fun and Enjoy!, Don Crano Akron, Oh NMRA #096211 mailto:donc@... Visit Model Railroading with DCC at: Join Model Railroading with DCC Web Ring. ----- Original Message -----
From: Mark Gurries <gurriesm@...> To: <TekScopes@...> Sent: Thursday, April 19, 2001 6:12 PM Subject: Re: [TekScopes] Tek 7904 Display Problem BTW Hi Mark Gurries glad to see you on the list.Hi Don. Been watching the list for a while. It was from one of your email on the DCC list that I learned about this list. Anyway... I told Jim Williams here at Linear Tech about this list. (My Lab bench is next to his.) But he is not one to use PC's. That Jim for ya. For those who are not familiar with Jim, he is one of out treasured assets at the company. Hi writes many application notes for our IC and tackling problems and parts that cause most of us to glaze over our eyes in terms of the accuracy or noise level requirements. Things like how do you verify all 24 bits of a 24 bit DAC! The trick around here to getting a Tek scope fixed and checked out by Jim Williams is to get an old 500 or 400 series scope in the lab. Tell Jim about it, and the fact that it does not work annoys Jim to no end. Before you know it, he is digging into the scope and fixing everything. Not that we cannot fix out own scopes mind you, but, Jim does a faster and better job than anyone I know. It fun to watch him and of course you learn along the way the history and debug tricks. We have about every make of Tek scope at the company labs. We have lots of 547's working in parallel with the latest Tek Scopes. We just got around to setting up an old 556 dual beam on another engineers lab bench. 454's are another favorite. A few of the guys have 7K stuff like yours. One of my employees has every 7K plug in made including some test adapters if I recall correctly. It amazing to see the latest scopes setup right next to an old classic. The biggest reason we like the old 400 and 500 series scopes is the very fine trace and excellent noise floor. When Jim sets up his 556 with two 1A4 plugins showing 8 traces that are all beautifully detailed (4 of the traces are on a different time base to boot) published in a App note, we sometimes get letters and calls about the scope photo alone! How did you do that? We think that our lab is one of the biggest consumers of electricity in Silicon Valley with all these Tube Tek scopes on and possibly the source of all the blackouts here in California. We already went though one air conditioner! ;-0 Best Regards, Mark Gurries gurriesm@... --------------------------------------------------------- Promotor of the DCC Standard for Model trains. Model Railroad Club and NMRA DCC presentations are at: -------------------------------------------------------- Audio Enthusiast (Love SAE equipment) ---------------------------------------------------------- To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to |
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Re: 465 Display Help Needed
Stan or Patricia Griffiths
CRT Mesh comment below:
dhuster@... wrote: A few comments on what has been offered so far.My understanding of the reason an expansion mesh was used in 465 and later vintage tubes was really to improve the vertical and horizontal sensitivity of the CRT such that expensive transistors would no longer be necessary in the vertical and horizontal scope amplifiers. It was mostly a manufacturing cost reduction measure with a spot size tradeoff. Not a good tradeoff, in my opinion. Compare the output stages of the 547, 453, and 454 scopes to what you see in the 465 and 475 and you will see what I am talking about. Stan w7ni@... |
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Re: 465 Display Help Needed
A few comments on what has been offered so far.
The characteristic fuzziness of a 465/475 and 7K scopes over their earlier cousins (and which apparently is NOT your problem since you describe major "focus" problems) is due to the inclusion of a scan expansion mesh within the jug through which the electron beam has to pass, causing a small amount of beam scatter. The mesh is there to improve geometry. If oscillations within the vertical system is the problem, then inputting a sine wave will show a thicker trace at the peaks and a thinner trace at the zero-crossing points. Also, you'll see the signal from the vertical deflection plate pins on back to the source of oscillation. Open elements inside the jug can cause defocusing. Don't forget that astigmatism and focus interact and one may be the problem where the other is not. If you can "round up" an unfocused stationary dot on the CRT with the astigmatism control, then focus is your problem. If not, the astigmatism circuit may be at fault. Make sure the LV power supplies are clean, correct and ripple-free. |
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Re: 465 Display Help Needed - another thought
--- In TekScopes@y..., ashtonb@j... wrote:
--- In TekScopes@y..., Kurt Graber <kurtg@s...> wrote:Isharp getthethe use of an HV probe. Can anyone tell me if I am looking in good...........................................right area or suggest any common failure modes? The low voltage that onetriggering)of the resistors has opened up. I have seen many cases !!! youdon't or sometimes ~ 200 MHz if all went well on that assembly..- tiny wiggles just visible on 54-A disappear into the thick trace ofAShton, yes I have heard that same thing about the 465, however after troubleshooting I am further able to describe the problem. The transition of the trace either falling or rising is poorly defined and instead of one sharp edge I see almost a centimeter of blur. I have been through the video output amplifier from one end to the other but I still have the symptom that any capacitance such as a scope lead hung on either vertical deflection output causes the amplifier to go into high freq. oscillation and the trace becomes a fog. I will press on but there is definitely something wrong with this thing. Bill |
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Re: 465 Display Help Needed - another thought
Stan or Patricia Griffiths
billw101@... wrote:
AShton, yes I have heard that same thing about the 465, however afterHi Bill, I would take a close look at the input FET's to make sure they are the original type. Sometimes they will short or open and the repair techinician will use whatever FET is handy and not bother with the correct part. This can cause all sorts of oscillation problems and stuff like you are seeing. Stan w7ni@... |
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Re: 465 Display Help Needed - another thought
--- In TekScopes@y..., Kurt Graber <kurtg@s...> wrote:
sharp thefocus on the trace with any combination of intensity, focus or getexception of the high voltage, crt bias and cathode bias, until I ...........................................the use of an HV probe. Can anyone tell me if I am looking in the
circuit that the focus and astig tap into.that one of the resistors has opened up. I have seen many cases !!! youdon't need a HV probe , just take your meter and ohm them out. They will notappear burned but they have a tendancy to open up due to the highvoltage.......this will cause an unsharp trace and many cases no trace at all (just ahaze)...Good LuckAnother point: the 46x, 47x series just wasn't as sharp as the tube scopes! or even and especially - the 454, 454A. Some engrs. think the 454A best 150 MHz scope ever (2mV/DIV, all the delay triggering) or sometimes ~ 200 MHz if all went well on that assembly.. I can see the clear difference bewtween say, a 475A and the 454As - tiny wiggles just visible on 54-A disappear into the thick trace of 475 (or 465). Just in case you're trying to do better than it Can! Ashton |
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Re: *Cheap* Equipment sources
--- In TekScopes@y..., Michael Dunn <mdunn@c...> wrote:
Just a little poll of sorts: I'm wondering where we all findold equipment -- at least the stuff we get for real cheap!stuff at "garage sales" held at a local university. We're talking REALHello Michael, and thanks for helping me get past the sign-on glitch. As you can see, posting now works too [I think - we'll see]. I started accumulating Teks (beyond a couple for use) ~ 3 years ago pre- eBay for me.. A fireman in LA had an ad in Nuts&Volts.. ended up sending along an initial 10ish scopes (mostly 453s) and a year later, more things. Truck rate and such seems about only way to handle high ship'g cost, but that means ~ 300ish # to come out reasonably. This may not be true in '01 (?). Now I have to read some back posts. I've mainly used Tek scopes forever - only lately repair / calibrate, but without the tricks that experience teaches (might tell about the 2430 with no warning about needing an extra fan - except buried in the Service Manual. Ugh. All those labels about imploding CRTs but - not one saying "cool it - Now!") Ashton Brown Sonoma county, No. Calif. |
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Re: *Cheap* Equipment sources
Jams & Kandy Nunn
I started my collection with a 535a that I purchased at a garage sale for $1. The scope came with CA plug-in and a set of probes. I always admired the Tek scopes from the 60's and thought that it would be fun to fix it or take it apart. I ended up doing both and spending a lot more than a buck to get it working. My other "sea story" is a 545a that I purchased from a TV station last year. The scope was calibrated! has the "old" style cart, 4 probes, a CA and a M plug-in and a 1L5 (not working) all the original manuals and I found the original purchase order in the operators manual compartment, total cost was $60.
Most of what I purchase I find on E-bay or the TRW swap meet (I live in LA). Jim Nunn |
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Re: 465 Display Help Needed
Kurt Graber
billw101@... wrote:
Hello, I have been pulling problems out of a 465 that I recentlyA common problem or failure is the opening of the voltage divider circuit that the focus and astig tap into. I am unfamilier with your particular scope but the chances are good that one of the resistors has opened up. I have seen many cases !!! you don't need a HV probe , just take your meter and ohm them out. They will not appear burned but they have a tendancy to open up due to the high voltage.......this will cause an unsharp trace and many cases no trace at all (just a haze)...Good Luck |
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Re: *Cheap* Equipment sources
Michael
I and a friend on this list have found pretty much all our stuffGee, half your luck! I've never seen any Tek stuff at garage sales (not that I go to many), and paid A$600 (around US$1200) for my (as new) 7603; but I was given a TM503 with a DM501A (faulty) and three plug-in kits in exchange for a satellite TV receiver. Meanwhile I have (mostly) fixed the DM501 and keep looking... :) Kind regards, :) Michael |
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Re: *Cheap* Equipment sources
ronald h. driggers
I paid 25 for the 545a, most of the plugins cost 15 to 20, bought one on
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ebay as well as some of my manuals, some of the stuff is in a salvage yard, near by, but they run 25 to 45 dollars depending on the size and weight, they look at the scrap value, bought the ca and the 130 lc meter this weeking for 20 dollars for the two, more than i want to spend but i am in a bad area for old tek stuff. I have found others but can not pay shipping. You seem to buy much cheaper than i can, the 556 i got was 20.00 dolllars, may not be an easy repair though. Since this is a hobby cheaper would be MUCH better for me. I have payed more for manuals than equipment. ----- Original Message -----
From: Michael Dunn <mdunn@...> To: <TekScopes@...> Sent: Monday, April 23, 2001 10:17 AM Subject: [TekScopes] *Cheap* Equipment sources Just a little poll of sorts: I'm wondering where we all find old |
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*Cheap* Equipment sources
Michael Dunn
Just a little poll of sorts: I'm wondering where we all find old equipment -- at least the stuff we get for real cheap!
I and a friend on this list have found pretty much all our stuff at "garage sales" held at a local university. We're talking REAL cheap. C$10-$20 (U$7-14) for anything from a 502A to a 549 or 556! $5 for a plug-in. Usually in very good condition. How about you? ----------------------------------------------------------------- Michael Dunn | Surround Sound Decoder & Stereo Enhancer Cantares | Self-Amplified Speakers, Test Equipment 74 George St. | Ambisonic Surround Sound CDs and Recording Waterloo, Ont. | (519) 744-9395 (fax: 744-7129) N2J 1K7 | mdunn@... Canada | ----------------------------------------------------------------- |
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465 Display Help Needed
Hello, I have been pulling problems out of a 465 that I recently
acquired. The last remaining problem is the inability to get a sharp focus on the trace with any combination of intensity, focus or astigmatism. I have checked everything in the CRT circuits with the exception of the high voltage, crt bias and cathode bias, until I get the use of an HV probe. Can anyone tell me if I am looking in the right area or suggest any common failure modes? The low voltage supplies all check good and noise free. Thanks for any help. |
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