Dark CRT of Tektronix 576 curve tracer - diyAudio
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Old 1st January 2013, 05:11 AM   #1
chanwoo is offline chanwoo  South Korea
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Default Dark CRT of Tektronix 576 curve tracer

Dear. Friends

I recently bought defected Tektronix 576 curvetracer to pass time.

I found step generator is not oscillating because rusty ICs pin. Replaced all of them. However major trouble is low intensity of CRT. I checked HV for CRT and actual voltage was 3.2KVDC but it suppose to be 4KVDC. And 6.3VAC heater voltage and it's lit fine.

When I turning intensity contron from low to high the spot or line on CRT the intelsity increasing was not linear. The intensity is changing from dark, low, mid low, high and mid low again on it's way. Therefore I have to negotiate with 60% of intensity control position to get maximum intensity but the intensity is still not enough. Really hard to see line on CRT when the spot on CRT is stratching as a line.

Focus control works fine because spot is changing oval shape from horizontal to vertical.

Here is my question, Is HV3.2KVDC not enough for this CRT to get enough intensity or the CRT immission too low?

It is very hard to find replacement of the CRT. Has anyone solution or apare part for sale?

Thank you in advanced.
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Old 1st January 2013, 05:26 AM   #2
freax is offline freax  Australia
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Has the intensity pot been cleaned?

I would check that and whatever it connects to for dry joints.

Have you checked the B+ voltage and other power supply voltages? If you are getting low HV then its likely that the power supply feeding your flyback is lower too.
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Last edited by freax; 1st January 2013 at 05:44 AM.
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Old 2nd January 2013, 02:50 AM   #3
chanwoo is offline chanwoo  South Korea
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Freax,

I checked the intensity pot using DVM and the pot works good. Also I found the spot light is scattering when I turn intensity pot to full clockwise. (dark, low, mid low, high and scattering) Which means spot is scattered when I turn intensity pot to full clockwise)

I have checked all power supply voltages and all they are within spec.

I don't know what reason the spot is scattering? I will attach photo for your reference later.

Thank you.
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Old 2nd January 2013, 01:05 PM   #4
chanwoo is offline chanwoo  South Korea
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Here are videos for your reference.

Tektronix 576 curve tracer low intensity - YouTube
Intensity control is not linear when turning intensity pot.


IMG 1511 - YouTube
Multiple lines for another example. More lines on CRT then dark more and more.


IMG 1512 - YouTube
What is this? Vert 20uA, Horiz 2V and turning variable collector supply dial. Is this noise?
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Old 3rd January 2013, 07:30 AM   #5
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Try TekScopes : All about classic Tektronix CRT o'scopes lots of experts hang out there.

Good luck,
Jaz
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Old 8th January 2013, 06:55 PM   #6
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What do you mean when you say "Scattering"? Do you mean the spot gets bigger or that it moves? What did you measure the high voltage with? Tek usually used a Tripplet 630 VOM. 20000 ohms pre volt, 6000V range means 120 Meg input resistance. I would suspect a high voltage problem.
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Old 9th January 2013, 04:32 PM   #7
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Quote:
Originally Posted by chanwoo View Post
When I turning intensity contron from low to high the spot or line on CRT the intelsity increasing was not linear. The intensity is changing from dark, low, mid low, high and mid low again on it's way.
This is called "double peaking", and it means the CRT is near the end of its life

Some things to try:

1. CRT rejuvenation: CRT Restoration for the (Brave) Experimenter

2. See if anyone on the TekScopes mailing list has an extra CRT

3. Connect an external display

4. Wedge in an LCD module
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