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Re: Searching for a Tek 7000 series scope
On Sat, 20 Apr 2019 14:42:00 -0700, you wrote:
Harvey,Ah, now, based on my lab: 1) PC board fabrication, about 5 feet by 2 feet. 2) DC calibration (one rack and desk space) 3) RF work, maybe the same 4) Digital (main focus), about 4 feet worth of space) 5) Scope calibration (2 feet, often borrowed) 6) miscellaneous (borrowed, you decide) 7) PC board assembly and desoldering (4 feet) 8) plugin stack and tool chests (4 feet) 9) place to sit (3 feet) (!) 10) door (needed one of them somehow) 11) window (etc...) You're getting the idea.... Labs automatically expand to 2x the available space..... Harvey
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Re: TEK 475 voltage issues.
All,
I just wanted to wrap up and let you know where this ended up. My last post I was fighting an issue with the -15v rail. Now, when I started working on this scope, the -15 was fine. Sometime during my work, this rail died. The first item I found was a shorted C1478 10uf tantalum. Also, this appeared to fry Q1474, Q1478, and U1464. Who knows which one actually started this chain reaction but that is what I had to replace to get the -15v. Now ALL the voltages are great and the scope is beautiful! Since wrapping up this project, I restored a Heathkit TC-2. Now, I'm looking for a VTVM to work on! Many thanks for this forum! Glen |
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Re: Searching for a Tek 7000 series scope
Hi Sean,
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OK, I looked at the pictures. The third picture really caught my attention!!! My first reaction was "This is not possible". The bandwidth must be so far down at 2GHz that you would barely get it to display that at one or two divisions of vertical no matter what you did. What I don't understand is what you had to do to get that 2GHz sinewave on the screen of a 7904A with a just a 7A19. Also how hard was it to get the 7B15 to trigger at that frequency? One last question: What was your signal source? My complements to you for whatever you did to get your new scope to do that. Everybody should sit up and take notice of what a 7901A can do. It would be even faster with a 7A29 in it. You are certainly capable of putting this scope to very good use. Dennis Tillman W7PF -----Original Message----- -- Dennis Tillman W7PF TekScopes Moderator |
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Re: 7S12 with S-4 and S-53 troubleshooting
I think that offset-feedback loop is not affected by lack of sampling, so
offset control is still functional (just as the input signal were always zero). Feedback signal enters the head at pins 2&B, and has an uninterrupted path through gate bias resistors, forward biased D20, D23, D25 and D28, and Q36. You are correct that offset is balanced in Memory to keep feedback (actually gate of Q36) constant and ready for integration of whatever comes from the gate. I was also confused how this circuit deals with offset being DC, and S-4 preamp not passing DC (C41, C50). Apparently the pulser baseline offset correction circuit (schematic 15 in the manual) feeds pulses to the feedback circuit at the head, to which memory also responds. I did not dive into details of this circuit and I hope I'm not mistaken, in any case I observed these pulses throughout the whole preamp-offset-memory-feedback loop, having the snap-off non functional. I'd also like to hear other members opinions, hope more will join this discussion after Easter. Best Regards, Nenad On Sat, Apr 20, 2019 at 11:30 PM Albert Otten <aodiversen@...> wrote: Hi Nenad, |
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Re: Searching for a Tek 7000 series scope
Hi Sean,
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Congratulations on capturing a 7904A - it is an astounding instrument. It was nice of John Griessen to offer you one of his scopes. Most of the scope carts that are wide enough for a four wide 7000 scope have another thing you can add later on: The side rails that are mounted to the main shelf so they swivel with it are wide enough to accommodate a TM504 mainframe so four additional TMxxx plugin instruments can go with your scope at all times. You will have to find the shelf Tek made for this purpose. There is nothing special about it so I made two of them for my own use and mounted two TM504 mainframes onto those side rails. The shelf is a flat surface and on the left and right sides it is bent up and holes are drilled in the bent up sides to mate to the side rails of the scope. By adding the shelf you actually strengthen the whole cart. Two shelves and two TM504 mainframes worked perfectly and allowed me to take up to 8 plugins where ever the scope was. the scope cart is so well built it was perfectly capable of handling the extra weight without any problems at all. Dennis Tillman W7PF -----Original Message-----<SNIP> I wanted to thank everyone for their replies, direct emails, and -- Dennis Tillman W7PF TekScopes Moderator |
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Re: Searching for a Tek 7000 series scope
One can also find three-shelf heavy-duty plastic carts that work well as ¡®scope carts. I have one made by Rubbermaid on which I kept a Tektronix 575 for many years.
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DaveD Sent from a small flat thingy On Apr 20, 2019, at 17:05, Harvey White <madyn@...> wrote:On Sat, 20 Apr 2019 13:12:15 -0700, you wrote:I have a scope mobile cart that will hold a 7000 series scope (no, not |
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Re: Searching for a Tek 7000 series scope
Sean,
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Good choice. The Tektronix model 204-2 ¡®scope cart is made specifically for the 7000-series ¡®scopes. It has five slots that hold spare plug-ins as well as a drawer that may be used to hold probes and accessories. It also has a hold-down bar to keep the ¡®scope from sliding around on the cart. Specific carts are often dfficult to find and they are a bit difficult to ship (but, with some work, they can be diassembled for more convenient shipping). Good luck. DaveD Sent from a small flat thingy On Apr 20, 2019, at 16:12, [email protected] wrote: |
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Re: SMA caps for sampling heads
Hi Reginald,
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How did you find out the operating hours and power up figures? I have an 11403A and there is nothing in the Utility Menus that would give me that kind of information. Just a wild guess but given your figures the 11801 was running an average of 22 hours each time it was powered up. Could it have been in some kind of installation where they used the scope on a daily basis, but always shut it off at the end of the day? To make another even wilder guess, if it was used all day long and into the night before being turned off each time then it would make sense to assume it was used for 22 hours per day on average for 2,000 days average. That comes out to about 500 days that it was used. That would equate to about 2 years that it was in use like this. This is nothing more than wild speculation on my part. I must be momentarily bored. More likely I am avoiding something unpleasant I have to do. Dennis Tillman W7PF -----Original Message----- -- Dennis Tillman W7PF TekScopes Moderator |
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Re: Searching for a Tek 7000 series scope
Harvey,
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Thanks for your thoughts. Right now I definitely don't have the floor space for a scope cart, but I'm planning a move in the near future and am looking at houses. One criteria is enough floor space for a couple of benches and rolling carts (already have a small rolling metal cart I got at the container store which I keep my small tools on, such as screwdrivers, pliers, flux bottle, etc on. Sean On Sat, Apr 20, 2019 at 02:05 PM, Harvey White wrote:
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Re: 7S12 with S-4 and S-53 troubleshooting
Hi Nenad,
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I agree that the avalanche pulse alone is probably so slow that the clipping lines simply act as a shortcut. But how to explain the response to the Offset control? When you change Offset then this change is balanced by an opposite change in Memory voltage in order the maintain the same voltage at feedback pins 2 & B of the S-4 connector. When the S-4 does nothing then that feedback voltage would change freely and Memory would not change at all. What is wrong in this reasoning? Albert On Sat, Apr 20, 2019 at 11:12 PM, Nenad Filipovic wrote:
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Re: Searching for a Tek 7000 series scope
Hi Sean,
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Where are you located? Dennis Tillman W7PF -----Original Message----- -- Dennis Tillman W7PF TekScopes Moderator |
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Re: 7S12 with S-4 and S-53 troubleshooting
Hi Albert,
In my case (without the snap-off signal) the head sensitivity to input signal was zero. The explanation is in the structure of the strip line to which C52 and C54 are attached. This structure has (intentionally) a very low inductance, making it a very high frequency tuned circuit with respect to its own capacitance (these parameters guarantee the specified high rise time of the gate strobe signal, which is the key parameter of S-4 design). Slow dv/dt signal off Q69 could never produce a large enough voltage on it to forward bias the gate diodes. However given the ratio of C52/C63 and C54/C64 dividers, Q69 can reverse bias the snap-off diode D61. Reverse recovery process of D61 yields the high dv/dt (high harmonic content) snap-off pulse, to which the strip line resonator will now happily react. R50 fine tunes the Q factor of this circuit (its transient response). Therefore without the fast snap-off pulses, input gate diodes will never conduct. What kept being confusing during my troubleshooting was the presence of sampling pulses in the signal path (all the way to vertical output). At first I could not tell whether these were coming from the input gate (which would imply a working snap-off), or somewhere else. Later I determined that these are present in the complete memory-vertical amp-feedback loop, leaving no guarantee that the gate is sampling at all. Being sure that gate is functional (my previous tests) I focused on the snap-off, and that's how I found the issue. I was very lucky, I have no extension cables for S-4, and snap-off board is completely inaccessible when S-4 is inserted in 7S12. Best Regards, Nenad On Sat, Apr 20, 2019 at 10:07 PM Albert Otten <aodiversen@...> wrote: Hi Nenad, I overlooked your second last message in which you answered my |
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Re: Searching for a Tek 7000 series scope
On Sat, 20 Apr 2019 13:12:15 -0700, you wrote:
I wanted to thank everyone for their replies, direct emails, and advice. After consideration of many kind offers, I ended up purchasing a 7904A + plugins from John Griessen. It arrived yesterday! Absolutely thrilled with it.I have a scope mobile cart that will hold a 7000 series scope (no, not for sale). Some observations: The scopemobile was designed to be a roll around home for a scope in a lab/facility that had a lot of bench space. The typical electronics bench of the time was a workbench maybe 35 to 40 inches deep, relatively high off the floor (people used stools), with a single shelf about 2-3 feet above the workbench. You'd put instruments, etc., on that shelf. However, given the depth of the average 7000 series scope (and that there'd not likely be one for each technician, either), the scope would not sit on the bench. Hence, the scope cart with plugins, TM500/TM5000 stuff, etc. Point is, they had a lot of floor space. Your lab may not. Mine doesn't, so my scope cart is sitting elsewhere waiting for a larger lab.... (one day). Now, as far as my arrangements go, and you may want to consider this, I use the roll around wire shelves, 4 feet wide, 2 feet deep, 6 feet or so high, with six shelves (not all necessarily used). You *really* want the kind that does not have that little helpful basket shape, you want the kind where things could roll off, with the flanges down. (BJ's wholesale seems to sell on the turned up type, good for boxes and bins, not so hot for test equipment. I took a power strip and bolted it to the back of one of the shelves. I took a closet flourescent lamp and bolted it to the back of the top shelf. Saves needing a flashlight. I then went to the local Home Despot and bought a sheet of 4x8 1/8th inch masonite (brown particle board to others, but without the holes). I had them cut it into sheets that exactly fit the top of the shelves, closing off the wire holes. Now everything with feet doesn't catch on the shelves. One of those shelves is an inch or so off the main workbench surface, and behind it. The 7000 series scope rests on the back of the shelf and with the bail down, is at a slight angle when resting on the workbench. This works for me. Striplights on the shelves for background lighting on the bench, outlet strips below the bench, and so on. You may not use that scope cart as much as you might think, depending on your lab layout. Harvey
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Re: Searching for a Tek 7000 series scope
I wanted to thank everyone for their replies, direct emails, and advice. After consideration of many kind offers, I ended up purchasing a 7904A + plugins from John Griessen. It arrived yesterday! Absolutely thrilled with it.
/g/TekScopes/album?id=89735 I think the next thing I need to find is a scope mobile cart for it to free up bench space. :o) Sean |
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Re: 7S12 with S-4 and S-53 troubleshooting
On Sat, Apr 20, 2019 at 04:45 PM, Nenad Filipovic wrote:
Whaw Nenad, what a good luck that you discovered the fault in S-4/R62! Congratulations. I tried to understand what happens when R62 is interrupted. The snap-off diode receives no bias current but the avalanche transistor Q69 will still function and send a kind of strobe pulse to D2F (and not to D2A, so totally unbalanced). The bridge might more or less response but with extremely bad efficiency. If so, it is similar to extremely heavy smoothing because of which your sine wave reduces to an average value. But also response to sudden Offset changes would be very slow. Do you remember if that was the case? You didn't try DC input is it? My "theory" might be wrong in that the avalanche pulse is far too slow to proceed further then the clipping line. But then I still don't understand how Offset could function. Albert |
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Re: 7L5 knob removal
It's alive - sort of. I had to perform quite a bit of surgery on the guts. I found that the mounting posts on the big board that attaches to the right side RF module had broken loose from the board, and a board edge connector socket on it that joins the back interface cluster board, was split down the middle. The posts were easy to tap through and put screws in from underneath, then I straightened out and realigned all those %^^*% long inter-board square pins.
I didn't have the right kind of board edge connector in stock to replace the busted one, and I was concerned about removing all those socket pins from this multi-layer board, so I opted to put a steel band around the socket housing, which drew everything back in pretty well. The front casting did have some cracks in the skimpy areas, and I couldn't flatten it out quite right without risking major fractures, so it still has a bit of concavity. The front plate did flatten out OK, so it looks good assembled, even though the casting behind it dips inward. I put it all back together sufficiently to plug into a mainframe, but it's still a little (and too much) out of square, so will need more mechanical tweaking. I plugged it in and fired it up, and it immediately crashed the mainframe. I figured a bad Ta cap somewhere deep inside was the problem. However, forcing the right side of the plug-in in deeper made it come to life. So far it has most of the readouts and knob functions indicating, and a baseline, but apparently no video signal. The sweep time/div readout is stuck at "500 kHz" regardless of the knob position, although there's evidence that the actual setting is doing something inside. I'm next going to loosen up the back end rail mounting screws so there will be a little more play side to side, and hope that getting deeper engagement on the right will fix the remaining problems. If not, it could be that I missed or connected something wrongly on assembly, or knocked something loose, or it already had a fault, etc. I'm happy that at least it lights up though. Ed |
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Re: 7S12 with S-4 and S-53 troubleshooting
Heh, I just fixed it, it's working now. While probing all components inside
S-4, I found that the bottom lead of R62 was cold soldered (the one soldered to the gold plated PCB strip), it snapped off at some point and was floating. I noticed it only after touching it with probe tip and seeing it move, otherwise it was undetectable. After fixing this soldering everything came to life. Regardless of this S-4 issue, the dreaded TI IC sockets are a nightmare. Even though all IC leads are clean and shiny in my 7S12, the sockets act out. The previously posted "Morse code" trace was the result of that, with proper contact the trace is pretty much continuous. Will need to replace them all. @Albert: Thank you for your help. Hope I get some more heads for this setup to make it a bit more useful. Best Regards, Nenad |
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