Author Topic: Tektronix 7854 Oscilloscope Blurry CRT and plugins  (Read 467 times)

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Offline Ordinaryman1971

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Tektronix 7854 Oscilloscope Blurry CRT and plugins
« on: August 11, 2018, 12:50:20 am »
I’ve got this 7854 with completely unreadable screen. I can see the traces but everything else is so out of focus I can’t really recognize any letters or numbers.
Also, I have few plugins but wanted to ask if there was some kind of default set of plugins that was shipped with this scope and what would be optimal set of plugins for everyday use.
Plugins I have are:
7b53a dual time base x 2
7b85 delaying time base
7b80 time base
7b92a dual time base
7a13 differential comparator x2
7a26 dual trace amplifier
Are all those plugins usable in this scope?
I’ve plugged the plugins in the A and B slots on the right so I have two time bases there.
I can see the traces on the pictures I will try to include.
When I plug something in one of the horizontal slots on the left the frame hangs and doesn’t pass the self test.
How to test all the plugins and see what’s working and what’s not.

 

Offline particleman

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #1 on: August 11, 2018, 02:48:49 am »
The last 7a26 plugin I got needed tantalum caps changed. Several were shorted, plugging it in caused the scope to not power on correctly. Changed caps and all works well now.  7k extender will make things easier.
 

Offline Ordinaryman1971

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #2 on: August 11, 2018, 03:41:42 am »
Here are some screen shoots with unreadable and out of focus numbers on crt
 

Offline ignator

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #3 on: August 11, 2018, 03:45:19 am »
The good thing is that it mostly appears to be working.Open the case, and measure all the power supply voltages per the schematic. It's possible the previous owner messed with one of the focus magnets or grid voltages, and such. The manual should give an alignment procedure to follow.
 

Offline tautech

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #4 on: August 11, 2018, 05:29:27 am »
I’ve got this 7854 with completely unreadable screen. I can see the traces but everything else is so out of focus I can’t really recognize any letters or numbers.
Also, I have few plugins but wanted to ask if there was some kind of default set of plugins that was shipped with this scope and what would be optimal set of plugins for everyday use.
Plugins I have are:
7b53a dual time base x 2
7b85 delaying time base
7b80 time base
7b92a dual time base
7a13 differential comparator x2
7a26 dual trace amplifier
Are all those plugins usable in this scope?
I’ve plugged the plugins in the A and B slots on the right so I have two time bases there.
I can see the traces on the pictures I will try to include.
When I plug something in one of the horizontal slots on the left the frame hangs and doesn’t pass the self test.
How to test all the plugins and see what’s working and what’s not.
Mainframe:
http://w140.com/tekwiki/wiki/7854
Plugin list:
http://w140.com/tekwiki/wiki/7000-series_plug-ins
Avid Rabid Hobbyist
 

Offline Johnny10

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #5 on: August 11, 2018, 05:36:37 am »
You have tried the focus knob on the far right?

Takes a while to get used to setting up these scopes.
HP 3561A, Tektronix 2465A, HP8903B, DSA602A, Tektronix 7854,  HP3457A, Tektronix 575, 576,577, Datron 4000A, Fluke 181 Nanovoltmeter, Dos4Ever uTracer, Tek TDS7104 S, HP5335A, EIP534B 20GHz Frequency Counter, Ephratom M-110 Rubidium, Sencore LC102, Tek TG 506, 501 Calibrators
 

Offline Ordinaryman1971

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #6 on: August 11, 2018, 10:35:17 am »
Correct, i've tried all the knobs and everything that is accessible on the front of the unit.
There are some pictures with focus knob turned one way and the other...
 

Offline Ordinaryman1971

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #7 on: August 11, 2018, 11:20:43 am »
I've connected the signal gen and the trace is pretty nice and focused, it's the readout that's really bad.
I still can't quiet trigger on this trace, it's running through the screen but it looks good.
I've looked inside of 7A26 the dual channel trace amp and there is a bunch of tantalum caps, when I plug it in the frame it doesn't pass the self test...
 

Offline james_s

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #8 on: August 11, 2018, 11:31:59 am »
That trace looks pretty ugly to me, like there might be something wrong with one of the deflection amplifiers and the mangled readout is just a symptom. Look at how the gaps where the beam shoots off to draw the readout look all wonky.
 

Offline Ordinaryman1971

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #9 on: August 11, 2018, 04:04:40 pm »
I would like the readout to look that ugly and I would be very happy... just don't have an idea why would readout be that bad and the trace be... less ugly.
Will check the voltages tomorrow.... very nice piece of gear...
 

Offline james_s

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #10 on: August 11, 2018, 05:24:25 pm »
Look at the way the readout is drawn, it's made of a bunch of small vectors while the main trace has much longer straight sections. Also it may just be the photo but the display looks extremely bright in some of those pictures. Something is clearly wrong, and I suspect it's the same problem making the trace and the readout look ugly.
 

Offline floobydust

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #11 on: August 12, 2018, 03:36:03 am »
You have to narrow down what is not working - readout focus, readout character size, banding on the waveform display, crappy blanking etc.

The sine wave looks not so great, you can see two intermodulations causing banding and some sloppy blanking, presumably during the time slice the readout is displayed.

I would first ensure all power supply rails are correct and their capacitors are not bad.

The readout intensity and focus look way off. I can't tell where you have readout intensity or stored waveform intensity set on the front panel.

If the power supply is OK, you could try the focus switch/amplifier trimpots sheet 13, Focus gain R63, Focus output level R70.
Again, nothing should be that far off unless a component has failed, so trying to fix it by adjusting a trimpot has limits.

W140 Tektronix 7854 wiki
 

Offline Johnny10

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #12 on: August 12, 2018, 05:57:45 am »
What does the readout say?
Can't make out the characters.

Should be "Self Test Complete"

This pic from an Iphone is of my scope screen from 7854 1K sine wave.
« Last Edit: August 12, 2018, 11:28:45 am by Johnny10 »
HP 3561A, Tektronix 2465A, HP8903B, DSA602A, Tektronix 7854,  HP3457A, Tektronix 575, 576,577, Datron 4000A, Fluke 181 Nanovoltmeter, Dos4Ever uTracer, Tek TDS7104 S, HP5335A, EIP534B 20GHz Frequency Counter, Ephratom M-110 Rubidium, Sencore LC102, Tek TG 506, 501 Calibrators
 

Offline Ordinaryman1971

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Re: Tektronix 7854 Oscilloscope Blurry CRT and plugins
« Reply #13 on: August 12, 2018, 07:07:25 am »
Can't tell you, regardless of the settings I can't read it.
Will measure all the rails and report the findings...
 


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