Tektronix CSA803 CRT screen shaking.

[ZBIQ]

Hello!

I have recently bought Tek CSA803 for 47 euro (score!). It shows error E5322 but it is caused by two (dead) battery powered RAMs (it will be fixed by tomorrow). Next step is to buy SD-24 sampling head

But there is one very annoying thing. CRT screen is shaking/waving just a little bit, but it drives me MAD! I can not focus my eyes on the screen.

How can I fix this issue? I read about degaussing but service manual says that scope does that every switch on.
May it be tired caps near HV transformer and CRT peripherals?

I have never repaired CRT (I am 24 years old so I only used CRT as youngster) so could you help me?

Best regards,
Mateusz

[c4757p]

Got a strong magnetic field nearby? Like a directly adjacent fuckoff-huge linear power supply?

[ZBIQ]

Not really. Checked in the first place.

But maybe there is some noise in my room. I will try tomorrow, outside.

[vk6zgo]

Hello!

I have recently bought Tek CSA803 for 47 euro (score!). It shows error E5322 but it is caused by two (dead) battery powered RAMs (it will be fixed by tomorrow). Next step is to buy SD-24 sampling head

But there is one very annoying thing. CRT screen is shaking/waving just a little bit, but it drives me MAD! I can not focus my eyes on the screen.

How can I fix this issue? I read about degaussing but service manual says that scope does that every switch on.
May it be tired caps near HV transformer and CRT peripherals?

I have never repaired CRT (I am 24 years old so I only used CRT as youngster) so could you help me?

Best regards,
Mateusz

From the pictures on the 'Net,it looks like it uses a raster display turned on its side.
A lot of these raster displays are supplied by outside sources----Tek's own 650 series picture monitors were a bit of a nightmare,so let's hope it is an ouside sourced unit.

CRT displays obtain "boost HT" (that's what they called it in the valve/tube days so I still think of it as such),from an overwind on the EHT/horizontal o/p transformer.

It uses a fast-recovery diode as a half wave rectifier,followed by a low ESR electrolytic cap.

This normally supplies high voltage to both the horizontal & vertical output devices of the monitor.
There is initially a lower voltage supply which helps to get the horizontal circuits going,& then is replaced by this "boost HT ".

Any variation in this voltage may well cause your problem.

Do not use a normal Electtrolytic or a normal power diode in this circuit,as they will fail prematurely.

[ZBIQ]

I found one HV cap near CRT, 33uF/160V NICHICON.

So I will try to replace it by new one (low ESR ofc). Is it a good idea to change also the lower voltage caps?

[fivefish]

Have you gone through the service manual and check for any jitter adjustments (if any, on your scope model).

[ZBIQ]

Unfortunately service manual for CSA803 is rather brief through all boards...

What jitter do you want to adjust? Strobe signal for sampling heads?

In my opinion jitter is stochastic error and can not be simply adjusted by 'potentiometer'.

[ZBIQ]

YUPI!

I have replaced two battery powered RAMs and CSA803 mainframe is now fully operational. NO ERRORS! SCORE!
Now I need to buy sampling heads. There was SD-24 for 225$ on ebay but dude changed price to 580$

And there is my shaking CRT. Need to fix it fast!
https://www.youtube.com/watch?v=H4Ch6k-nYiY&feature=youtu.be

[fivefish]

In my opinion jitter is stochastic error and can not be simply adjusted by 'potentiometer'.

Tek probably didn't know that fact.

[vk6zgo]

Yes,the minimal jitter evident in the video looks more like an adjustment matter.

"Shaking" suggests a movement of the whole display raster.

If you can wind up the brightness on the CRT far enough,you should be able to see where the blanking ends and the normally viewable raster begins.

Adjust it till the transition between blanking & viewable area is just visible.
If the problem is as I earlier suggested,you will see a variation of its position on the CRT over time.

[ZBIQ]

I'm not sure I understand you correctly vk6zgo.

What exactly I need to do/observe?
I can increase "Lightness" of the screen by turning the front knob. I can also see transitions between 'dark area' and 'vision area'.

...you will see a variation of its position on the CRT over time.

But how fast it should move? Should it reposition as fast as 'jitter' (like on my video)?

[vk6zgo]

In normal picture monitors & TVs ,it is possible to adjust the vertical hold till the normally unseen vertical blanking interval is visible.
The edge of this will appear as a transition between "black" & white or grey.
If you have a vertical scanning fault,that edge will "jitter".

The reason I said to "wind up the brightness"is,if your display is in fact,a raster type,it normally operates with the screen black & is only  brightened where your trace & data ,etc appear.

The video looks more like there is a timing error between the scans & the data,however.

[ZBIQ]

Ok, I think I found something.

There is +70V going from A8 board (HV transformer, degauss and coil drive) to A7 board (CRT socket, color amplifiers).
This +70V had 1.5Vpp ripple - not to good. But all caps measured good ESR. So I added 100V 150uF cap on the A7 board directly (ripple has gone to 200mVpp). Also on A7 board was +15 and +5V volts - but no decoupling at all - to be sure I placed two 220uF low ESR PANASONIC caps on this low voltage.

I think there is some improvement .

[EVlab]

Hi there!

I have the same experience with my 11801c.

When I received the scope, I thought of a problem with the low voltage power supply or the voltage rails or the cabling. I measured everything with another scope. But, no ripple present. I replaced all capacitors on the A8 board, but it had only minor influence on the screen image bouncing / shaking effect. I have not tried to place additional caps on the A7 board.

It must drive you crazy, sitting 8 working hours in front of such a screen. I can't believe that ZBIQ and I are the only persons experience such a problem. The often referenced magnetic influence on the CRT should only be a problem of static deflection CRT, not on magnetic deflection like ours. Furthermore, these scopes where expensive, so I would not expect any influence by other equipment you may find on a normal lab bench.

Please keep me/us updated ZBIQ, and all others who may/can contribute!

Best, Simon

[meggerman]

Hi,
3 years onwards....
I have a Tek CSA 803 and had the screen shake, then realised it was a small magnifying florescent lamp I had switch on right next to the scope.
I switched that off and problem solved.
In the power supply section I have noticed what looks like a flickering neon light that seems to stay flickering for a short while after power off, even when you pull out the main power cable - no idea what it is yet.
Any CRT shake is likely to be low frequency internal/external magnetic interference, most likely external. One thing to try would be to disconnect the ventilation fan at the back as this is an easy item to rule out.
Hopefully you have solved the screen shaking by now.

Rob