CRT question

We already knew it's not the crt at fault. Another poster that asks and gets the correct answer, but remains entirely lost.

Reply to
tabbypurr
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Get the print even if you have to scan it. Send it to me. If you cannot get my email here I will give it to you. You send it to me and I will post it where I can hotlink to it.

Or don't you have a scanner ? Or did you build this purely from instructions ? You're not even telling us what this contraption is.

Reply to
Jeff Urban

Hogwash. I went back and read all the responses to my posts about this CRT. Most likely the CRT was not at fault but this was not known for sure. Now I know for sure the CRT is OK. Your reply does nothing to enlighten anybody. You have not posted anything useful. Why is that? You posted "Presumably the electrode voltages aren't staying the same as the thing sweeps across the screen." That's all you posted. Should I take what you presume as being true in all situations? In any situation? Why? And why did you presume what you did? How do I check what you said? I'm trying to learn, what are you trying to do? If I am lost then why not show me the way? When people ask me questions about machining I try my best to help, often with several explanations because some folks don't get it as easily as I do when it comes to machining. Please, if you can't bring yourself to help then don't waste your time responding to my posts, especially since I won't be wasting any more of my time reading yours. Eric

Reply to
etpm

How can you build an electronic circuit without having the schematic ?

Reply to
Jeff Urban

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** Wot a tedious wanker..

** Nope - those hogs are not in need of any washing .

** That is VERY good answer.

Every half decent CRT scope made uses balanced drive to the deflection plates - vertical and horizontal. There is a reason for doing so - it keeps the spot on the screen focussed.

YOU have the darn thing in front of you but are so dopey you cannot say if that is or is not the case with your simple kit scope.

FYI: When I was 17 and at high school, I saved my pennies and bought all the parts to to make a basic, 2MHz, 5 tube, 3 inch CRT scope.

My brother in law fabricated the steel case as an 18th birthday present - I still have it and it works fine - hence my affection for analogue scopes.

It uses balanced drive for deflection.

The focus is quite good.

.... Phil

Reply to
Phil Allison

Then I won't spend any further time clarifying either. Fool.

Reply to
tabbypurr

How ?

How can he know that, does he have a spare that acts exactly the same ? If so out with it.

I put it 50/50 between the CRT and the deflection drive.

And what the hell is this thing ? A dental scale ? A DVD rewinder ? What ?

Knows the CRT is not at fault, well then every voltage and waveform should be known to him. Is the plate drive balanced ? Can we at least know that ?

Reply to
Jeff Urban

(...)

Is the scope really a kit? How old? I've had a bit too much entertainment value from old carbon composition resistors that absorb moisture and change value. It might be worth checking the resistance of some of the resistors in the focus/astigmatism circuit. For example, here's something similar caused by an open 332K resistor: This is going to be difficult without a schematic. If you run out of options, perhaps tracing the focus/astigmatism circuit, measuring voltages, and scribbling a schematic might be useful.

I don't know for sure, but your logic seems sound. If the astigmatism problem remains the same, then the problem might be in the tube. If it changes when the X deflection leads are reversed, it's in the circuitry.

I've been trying to find a reasonable explanation of how the focus and astigmatism adjustments function. As near as I guess from what little I've found, the astigmatism adjustment compensates for axial symmetry errors in the electron gun. That brings up the possibility that the CRT might be sufficiently unsymmetrical to not allow astigmatism correction, or that the circuit or parts are so screwed up so as to not provide sufficient adjustment range.

From the TEK 5440 manual: To check for proper setting of the Astig control, slowly turn the FOCUS control through the optimum setting with a signal displayed on the CRT screen. If the Astig control is correctly set, the vertical and horizontal portions of the trace will come into sharpest focus at the same position of the FOCUS control.

...front-panel FOCUS and internal astigmatism controls have been incorporated for arriving at an optimum CRT display. FOCUS control R440 provides the correct voltage for the second anode in the CRT. Proper voltage for the third anode is obtained by adjusting Astig control R370. In order to obtain optimum spot size and shape, both the FOCUS and Astig controls are adjusted to provide the proper electrostatic lens configuration in the CRT.

So, how does the vertical astigmatism look? As bad as the horizontal or different?

Not much help, but maybe it will offer some clues.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

I built quite a few Heathkit kits in the distant past that did not require the use of a schematic. A schematic was provided by Heathkit, but it was only useful for learning how everything works and for troubleshooting.

I worked for a Heathkit store in the distant past for a few months. Most of what I found were the wrong parts in the wrong holes in the PCB. Occasionally, it was missing, extra, or substituted parts. Amazingly, I did find one design error. Heathkits spent considerable time and effort to avoid any assembly instructions or documentation errors. The unspecified manufacturer of this kit might not have been able to do as good a job. Methinks it might be worthwhile checking if there are any addendum, corrections, mods, or changes.

I can usually find someone else's mistakes rather quickly, but have had less luck finding my own mistakes. Maybe having someone else check the CRT circuitry for assembly errors might be useful.

Hint: That which is obviously correct, beyond any need of checking, is usually the problem.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

Yeah Jeff, it really is a kit. Here's the link:

formatting link
I wish I had traced out the circuit before I populated the board. But it's double sided and now really hard to see where traces go when they hide under components. Eric

Reply to
etpm

I did have someone check my work and he said it should work. And it does except for the changing focus. I am now thinking that somehow the voltages need to be changed. The heater voltage is just below the lowest voltage given on the spec sheet for the CRT. Nevertheless I am going to go back and check all the solder joints with a magnifier. And double check all the component values. The weird thing to me is that the thing works. It just goes out of focus gradually from one side of the display to the other. Thanks, Eric

Reply to
etpm

The video: It looks ok. No astigmatism, but plenty of smear (hummm?) on the digits. However, the photos on the home page: and Etsy: look much sharper.

Which CRT tube are you using? The data sheet on the Russian CRT is not very useful:

There should be some test points on the PCB with Vert, Horiz, and Sync signals. Connect these to an oscilloscope and reproduce the display. My guess(tm) is that it will either be perfect, which simply validates that you assembled most of the PCB correctly, or full of hum or oscillations, which suggest a circuit problem.

The aforementioned test won't do anything for testing the hi-v and CRT circuitry. However, there may be additional test points or inputs that can directly drive the vertical and horizontal amplifiers. This doesn't really prove anything or eliminate any possibilities, but it might be interesting to try.

I like to shine a flashlight from the circuit side so that I can see the traces. However, you're right that it would have been easier to do with a bare PCB. Maybe you can convince the seller to send you a photo or paper copy of the PCB? Here's a useless out of focus photo of the component side:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

Eric, have you tried contacting the kit maker? It may be a problem with the kit that he/she wasn't aware of - defective component, etc. It happens!

'howchon at hotmail dot com' (from the home page).

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup) 
                      John's Jukes Ltd. 
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Reply to
John Robertson

Rather off-topic, but in one of the pictures (uncaptioned, about 2/3 to

3/4 of the way down, where the clock is on a stepped, wooden base) the valves are nicely coloured - green on the left, purple top right, and blue bottom right. I assume these are simply non-functional valves with a coloured led hidden in the base. Those are pretty unusual colours for leds; maybe a white led with a coloured filter has been used. And are the valves non-functional? I would expect the base to get pretty hot with the filament at that end. Not a good environment for an led.
--

Jeff
Reply to
Jeff Layman

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** Likely the valves are not operating and the rather bright light is coming from thin ,coloured filament bulbs - as used for xmas decorations and tree lighting.

The hole in the bottom of a 9 pin valve base is not very big.

.... Phil

Reply to
Phil Allison

LEDs in all sorts of oddball colours do exist, they're just a good bit more money & thus unpopular.

NT

Reply to
tabbypurr

Yes, I did contact him. He has tried to help but so far nothing. Eric

Reply to
etpm

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