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Re: 7904 problems
Morris,
If something had come loose inside the CRT wouldn¡¯t we expect that the symptoms might change with orientation? I haven¡¯t tried rotating the instrument (which is more difficult for you than for me), but I have tried tapping the case to see if the distortion moves (it doesn¡¯t, but I wasn¡¯t tapping very aggressively). I will try operating the scope horizontally as well as vertically and see if that makes a difference (which would, I think, confirm the hypothesis of CRT damage). I¡¯d really like to see some pictures of what your 7904 is doing, just to verify that we are seeing similar faults. ¡ª Jeff Dutky |
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Re: 7904 problems
John,
I know, it¡¯s very strange looking. I¡¯ll set the scope up as you advise (except for ¡°pushing the VER knob¡± as that¡¯s not a thing on the 465B: I¡¯ll just rotate all the VAR knobs into the calibrated position) and get some more pictures with the trace at different vertical positions. The square wave looks the way you would expect in the lower half of the screen, it¡¯s only when you cross the centerline that the distortion starts. Tom, I¡¯ll try to get voltage readings, but my bench is currently occupied by another, unexpected project. Checking the signals going into the plates is excellent advice (as always), but I will need to clear the bench before I can do that. ¡ª Jeff Dutky |
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Re: Super Clean 570 Curve Tracer on Craigslist
That thing looks like it rolled off Tek's assembly line just yesterday. Very nice!
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Thanks, Barry - N4BUQ ----- Original Message -----
From: drawding@... Hello, |
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Re: Possible Replacement Switch Fingers for 7000 Plugins
On Fri, Feb 11, 2022 at 01:46 AM, Jeff Dutky wrote:
The RPR has a long list of instruments they are used in. In short they are TM500 plugins, 150x, 178, 300-ser, 400-ser, 600-ser, 57x, 5000-ser plugins and 7000-ser plugins & scopes. I'd say they are used in most, if not all, switches with a cam-drum that are not the HF version. /H?kan |
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Re: 7904 problems
Don't know how to label what that photo looks like. With a square wave, the lit part of the trace on one line should be exactly above the off part of the other line. this looks particularly strange in the middle of the screen one division below the top of the screen where there are more cycles displayed than on the bottom trace.
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Set the time/div to 1 mS and push in the VER red knob to better examine this. Adjusting the scope probe would give a better picture also (the adjustment slot in the hole in the BNC connector housing. John On 2/11/2022 2:11 AM, Jeff Dutky wrote:
Morris, |
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Re: 7904 problems
Tekscopes troubleshooting rule number 1: Check all the power supply voltages.
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I recently had a similar problem on a 7904 except my distortion was at at the bottom of the waveforms. Turned out to be low -15V . If I were a betting man I would guess your +15V is low.. . The power supply stack is a PIA to troubleshoot and the +15V? problem ( if that is what it is ) can be in the supply or one of the boards that +15V feeds ....Have fun Dave NR1DX manuals@... On 2/11/2022 1:31 AM, Morris Odell wrote:
Hi all,-- Dave Manuals@... www.ArtekManuals.com --
This email has been checked for viruses by Avast antivirus software. |
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Re: 7904 problems
Morris,
I have created a photo album with an image of the distortion I am seeing /g/TekScopes/album?id=272587 Does this look similar to what you are seeing? ¡ª Jeff Dutky |
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Re: 7904 problems
Bonjour Monsieur
Bravo to have acquired several of the great 7904, classic 400 MHz A photo of the screen displaying all aspects will be helpful 1/ shipping damage can ruin delicate CRT deflection plates, electron lens or gun 2 / deflection plate termination is on CRT neck, the pins can get disconnected 3/ HV power in CRT circuit affects beam focus Bon chance Jon |
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Re: 7904 problems
Here's what I'd do to make a definite diagnosis: Look at the vertical deflection plate voltages. If they look fine, then that pretty much leaves the crt as the only culprit. In that case, there's still a (slim) chance that the problem is external to the crt (e.g., a magnetized bit that is kinking the beam, although I don't recall any magnetizable bits being near the crt).
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-- Cheers, Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 2/10/2022 22:31, Morris Odell wrote:
Hi all, |
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Re: 7904 problems
Morris,
I understand the desire for this to be something other than a CRT fault, and that¡¯s mainly why I don¡¯t trust my (motivated) reasoning, but what are the chances that some chaotic destructive process would produce similar damage in two different CRTs in two different instruments? I¡¯m very interested to see other replies too. ¡ª Jeff Dutky |
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Re: 7904 problems
Morris,
by shear coincidence I just got a 465B what sounds like the same problem with the CRT: a kink in the traces in the upper half of the screen. I had thought (and still do, until proven otherwise) that this must indicate some damage to the tube itself, probably to the scan expansion mesh. Hearing that another scope has a similar failure, however, makes me skeptical. Specifically, if two scopes had damaged expansion meshes I would expect the damage to be in different parts of the screen, rather than both affecting the upper half. The distortion I am seeing affects both the vertical and horizontal axes. A level trace deforms in a wave-lake way as it moves higher up the screen, and a repetitive signal shows horizontal compression in regions of wave-like vertical displacement (I home that¡¯s comprehensible). I don¡¯t have any advice, as I have barely begun to investigate this issue myself, but I wonder if the location in the upper half of the display tells us something important. Maybe it¡¯s a failure of one half of the vertical amplifier? I¡¯m having a hard time imagining what kind of damage or failure would cause the observed symptoms. ¡ª Jeff Dutky |
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7904 problems
Hi all,
I recently picked up a couple of 7904s with a stack of plugins. While most of the plugins are OK, the mainframes have some problems. One of them looks very good but is completely dead despite having intact fuses. It doesn't even tick. The other looks like it's had a hard life but at least powers up. The vertical and horizontal systems work OK but the calibrator and the readout do not. Also the displays look Ok when the beam is at the lower part of the screen but develop a kink when it is shifted upwards. The geometry and astigmatism controls do not correct it. This happens regardless of the vertical or horizontal settings and al all timebase speeds. Is this a sign of a damaged CRT? I'd like to end up with two working 7904s but If the CRT is the problem than I might as well try to make one good one by swapping modules. Any advice gratefully received! Morris |
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Re: Possible Replacement Switch Fingers for 7000 Plugins
Tek had a number of different forms of these pieces. Some have solder posts, and some are made for riveting to the board. Some are just contacts to go from the mount, via the fingers, to the board pads. The high frequency contact types are different - the contact fingers are in pairs, on a tiny assembly isolated from the leaf spring/cam operator, with a molded plastic section. With these kind, the spring is typically grounded, and the isolated contact fingers bridge adjacent pads when actuated. These are what you'll find in the step attenuators. There may have been other variations for particular uses, in different lengths and mounting methods and such.
The bottom line is that the contact type depends on the application. If you're looking for replacements, your best bet is to salvage them from similar junked plug-ins, one way or another. Note that that ebay ad says the parts for sale are salvaged from TM500 plug-ins, and they appear to all be solder-in, plain contacts, which are useless in an attenuator. I don't know for sure if the 5K or 7K scopes use only the high frequency contacts for all functions, or if it's a mix depending on the use. As I recall, the 7K plugs I've seen all use the same kind - high frequency - for all functions, whether switching control states, readout encoding, or whatever. Ed |
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Super Clean 570 Curve Tracer on Craigslist
Hello,
Occasionally I will search nation wide on Craigslist for vacuum tubes. During a recent search, I came across this add for a 570 curve tracer Looks really nice and has all the test fixtures and a spare CRT. I am not sure about the price as I have a 576 and have never been in the market (or done market research) for a 570. I have no relation to the seller. Thanks, Dave |
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Re: New kid on the block...
Tim K4SHF
I turned 68 a few months a few months ago. I lost nearly 50% of my peripheral vision a couple years ago ago. Anything below horizontal is only a blur, my optic nerves swelled up, probably due to a lack of oxygen and when the swelling went down, those parts of the nerve were dead...it sucks but I could have easily woken up blind so thankful for what I have. Such is life! Thanks for the tips!
Tim K4SHF |
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