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Old 12th Apr 2011, 1:27 pm   #81
glowinganode
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Default Re: TEK scope excitement dashed

Well done Chris, that' not a bad looking trace.
Look like you still need to tweak the astigmatism and trace length (X-gain?) presets a little, otherwise the crt seems to be working well, certainly nice and bright.
Pic 4 on post #79 look like it was taken at high sweep speed with multiple triggering effects. Try triggering it externally from your square wave.
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Old 12th Apr 2011, 2:51 pm   #82
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Default Re: TEK scope excitement dashed

Great stuff!
At least it works now!

Maybe you need to feed a square wave and adjust the HF peaking the screw fell out of?
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Old 12th Apr 2011, 3:33 pm   #83
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Default Re: TEK scope excitement dashed

Well done Chris! Many more-experienced engineers would have given up by now! Top marks for effort! At the very least, you have learned a lot and are more knowledgeable about what goes on inside these things. Is the second beam working yet?


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Old 12th Apr 2011, 3:51 pm   #84
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Default Re: TEK scope excitement dashed

That's the next challenge, need to find the VR which will increase the gain so as to widen the scan line.

Chris
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Old 12th Apr 2011, 5:47 pm   #85
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Default Re: TEK scope excitement dashed

That is excellent progress Chris. I am very impressed, especially as if you'd sent it to most professional test gear repairers it would have been "BER" on hours alone.
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Old 12th Apr 2011, 6:15 pm   #86
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Default Re: TEK scope excitement dashed

If you don't have one already, it may be worth knocking up a simple calibrator - a square or pulse generator that produces known frequencies, pulse widths and amplitudes - there are several very cheap designs for these out there. Even an old Heathkit IG-4505 would be good - lots on eBay US for about 60 bucks... You could make one for a lot less... google "scope calibrator schematic" and a bunch turn up, including a modern version of the Heathkit design based on '74 series logic...

Having replaced the tube with another that is "sort of" compatible, you may find that vertical & horizontal sensitivity are now well out of calibration (the replacement tube may be subtly different from the original), so whilst you may get a trace that looks ok, getting any meaningful measurements off it may be another matter altogether!
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Old 12th Apr 2011, 7:25 pm   #87
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Default Re: TEK scope excitement dashed

Ch2 is now working, I reseated all plugs and connectors even though they looked ok.

I've also sorted the astig, read up on what you needed to do so the dot is nice and round when focused it was more like a sausage before.

Just need to find the x- gain to see if I can get the trace to fill the screen.

Chris
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Old 12th Apr 2011, 8:00 pm   #88
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Default Re: TEK scope excitement dashed

What can I say Chris? Very impressed Many would have abandoned this project considering scopes can be had quite cheaply these days. Excellent work.



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Old 12th Apr 2011, 8:29 pm   #89
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Default Re: TEK scope excitement dashed

Thanks for the kind comments Rich and others too, If it was not for the encouragement, advice, donor CRT and the occasional kick up the pants I would have not got far at all.

A bit more tweaking and the LOPT ring now looks as it should, i've left it running for a bit with chan 1 on the cal, and chan2 on the ring. Still a long way to go yet and I still can't find the gain to increase the horizontal trace line. Then there's the calibration as mentioned by Nicko.

Maybe, just maybe, my B'day pressie is going to be saved, or have I just murray'd myself.

Chris
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Old 12th Apr 2011, 8:52 pm   #90
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Default Re: TEK scope excitement dashed

Keep going Chris, you can not give up now!

cheers Mark
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Old 13th Apr 2011, 9:44 am   #91
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Default Re: TEK scope excitement dashed

Hi Chaps,

Today I located the X-axis Gain it was VR 395, however it has no effect on the trace width. Any further ideas on getting the trace full screen or is this the max I can expect. This is the last tweak required and it's done, then move onto the calibration.

Regards
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Old 13th Apr 2011, 9:46 am   #92
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Default Re: TEK scope excitement dashed

If this is like the 2215 then the horizontal gain is R752 on the XY amp / Horiz O/P module.
CRT driver looks like a standard tek cas-comp differential amp.
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Old 13th Apr 2011, 9:50 am   #93
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Default Re: TEK scope excitement dashed

Hi Dave I think they are different or am I getting confused I will check further.

Chris

EDIT:
no R752 on the component list, I'm searching the schematics of Horiz gain but not found it
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Old 13th Apr 2011, 11:03 am   #94
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Default Re: TEK scope excitement dashed

If you haven't got it already, the entire 2205 Service Manual is downloadable from http://www.danielvg.be/2205_SM.pdf

You want Figure 9-11, Page 9-37 (physical page 159 out of 181 of the PDF)

The 2215 is very different.

Cheers
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Old 13th Apr 2011, 11:19 am   #95
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Default Re: TEK scope excitement dashed

Hi Nicko, yep that's the one i've been working from.

Cheers
Chris
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Old 13th Apr 2011, 11:35 am   #96
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Default Re: TEK scope excitement dashed

Looks like the best adjustment is R744 (mag X1) then R777 (mag X10).
No adjustments on the main OP to match the tube.
page 5-12
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Old 13th Apr 2011, 12:18 pm   #97
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Default Re: TEK scope excitement dashed

Yep that helped it's within the graticule boundary now. The traces are nicely defined bright and focused. I have to pinch myself that this seems to be working, but I suppose "seems" is the key word here, guess I now have to build or buy the calibrator to see if this will actually represent itself correctly.

Chris
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Old 13th Apr 2011, 1:47 pm   #98
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Default Re: TEK scope excitement dashed

Well, what can you say but 'well done!'.
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Old 13th Apr 2011, 1:49 pm   #99
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Default Re: TEK scope excitement dashed

Quote:
Originally Posted by oldticktock View Post
Yep that helped it's within the graticule boundary now. The traces are nicely defined bright and focused. I have to pinch myself that this seems to be working, but I suppose "seems" is the key word here, guess I now have to build or buy the calibrator to see if this will actually represent itself correctly.

Chris
Looking very good & clean - to be Frank (even though I'm Nick), unless you are trying to do precision measurement from the scope, the internal calibrator will probably be good enough for most purposes - certainly initial setup - it is however a simple RC & opamp oscillator, so not too great.

A simple lash-up with an XTAL & some 74HC logic should do the trick!
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Old 13th Apr 2011, 2:00 pm   #100
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Default Re: TEK scope excitement dashed

Hi Nick,

To be honest I will be using it mainly on my 405 LineTV restores to look at the waveforms at certain points in the circuit, so perhaps precision is not required.

Still in for a penny..... I'm on this interesting path that I never expected to travel so I might as well see where it leads me. I'm quite intrigued about building this calibrator too (see pic), although I need to find a 100kHz crystal,a 2N3565 and a frequency counter.

It states "The calibrator operates on exactly 100 kHz providing a reference for calibrating the variable time base oscillator of general purpose scopes. For example, if the scope is set so that one cycle of the signal fills exactly 10 graticule divisions then each division represents 1 MHz, or 1 microsecond. If the scope is adjusted for 10 cycles on 10 graticule divisions. (1 cycle per division) then each division represents 100 kHz or 10 microsecends."

Although I found someone in the states who makes one and it has a variable trimmer and will send all in for £10

At least I know I can use the scope and the poor old TEK lives to fight another day.

p.s. you have to remember i'm a valve dude firmly stuck in the 405 era, transistors & 74HC logic alien to me

Chris
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