Tek 2211 CRT Weirdness

[GAD]

Bought this scope online for a good price with the screen advertised to look like this figuring I could tweak a trimpot and get it centered.



It's certainly displaying that issue, but it's also doing this:



Reading a cool old "diagnosing your oscilloscope" document from Tek that I found online, I adjusted the scope so that the trace filled the screen then took these two pics, one in focus and one out (controlled via focus on the scope):





My guess is that something bad happened during its long trek via parcel post (ugh). Any thoughts?

[ataradov]

You need to degauss it. There are ways of making a mains-powered degaussing tool out of transformer wire. Basically it is just a winding connected to mains. Turn it on, bring it close to the CRT, move it away slowly, turn it off when it is some distance away.

I'm sure there are other ways to get a degausser.

EDIT: Here is a commercial one - http://www.frys.com/product/487898

[GAD]

Hmm. I used to have a nice degausser from my mainframe days. We used to use them on 9-track tapes. There's no way I still have that thing...

I think you're right, though. I just took a strong magnet and put it near the unit and the distortion moves with the field.

[GAD]

Did some reading and found that a big 'ol Weller soldering gun is often used so I grabbed that and gave it a try. The screen wiggled as expected, and I did the proper dance and said the magic words, but in the end it had no effect. Bummer.

[ataradov]

Weller soldering gun

You need pretty strong field. If soldering gun has field strong enough, it probably will not pass UL tests.

You will need a real coil.

I just remembered, CRT monitors had a degaussing winding around the CRT. That can be used as well, but I don't know what is harder - to get a real degausser or old CRT monitor

[tautech]

Bought this scope online for a good price with the screen advertised to look like this figuring I could tweak a trimpot and get it centered.

http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[GAD]

Bought this scope online for a good price with the screen advertised to look like this figuring I could tweak a trimpot and get it centered.

http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

I found that. Great read!

[GAD]

Weller soldering gun

You need pretty strong field. If soldering gun has field strong enough, it probably will not pass UL tests.

You will need a real coil.

I just remembered, CRT monitors had a degaussing winding around the CRT. That can be used as well, but I don't know what is harder - to get a real degausser or old CRT monitor

Grumble.

[tautech]

Weller soldering gun

You need pretty strong field. If soldering gun has field strong enough, it probably will not pass UL tests.

You will need a real coil.

I just remembered, CRT monitors had a degaussing winding around the CRT. That can be used as well, but I don't know what is harder - to get a real degausser or old CRT monitor

Grumble.

Never seen one on a CRO. 

Notice now the waveform is corrupt on the right hand side.....this equates to the end of the sweep.....check the sweep triangular waveform for linearity.

[ataradov]

Never seen one on a CRO. 

I never seen a CRO that needed degaussing

I had a degaussing feature on my Daewoo CRT monitor. You would call it up from the menu, the picture would shake vigorously and after a few seconds be clear of any problems. I assume that thid was a standard feature on later models of all monitors.

[tautech]

Weller soldering gun

You need pretty strong field. If soldering gun has field strong enough, it probably will not pass UL tests.

You will need a real coil.

I just remembered, CRT monitors had a degaussing winding around the CRT. That can be used as well, but I don't know what is harder - to get a real degausser or old CRT monitor

Grumble.

Never seen one on a CRO. 

Notice now the waveform is corrupt on the right hand side.....this equates to the end of the sweep.....check the sweep triangular waveform for linearity.

From the sweep generator to the CRT final output stages.

Of course you'll need another scope to do so.

[GreyWoolfe]

I have, in the past, degaussed 27" TVs with a Weller soldering gun.  Worked great.

[N2IXK]

If degaussing the tube, shield, and mounting hardware doesn't help, it is possible that the CRT has been subjected to a physical shock that has displaced the internal deflection plates to cause this distortion.  A new CRT is the only cure here...

[dom0]

If the effect were 10 times weaker I'd say it's electrostic charges on the plastic card in front of the screen, but this strong (and this tube probably has some strong PDA, too)? Unless your scope was shipped together with a bunch of neodym magnets we are probably looking at another case of internal CRT damage by dropped parcel.

[chris_leyson]

Hi GAD well that was unlucky, but lets bust a few myths...

First myth: You don't need to degauss the CRT, there isn't enough steel in a 2211 to generate any sort of magnetic field, and even if there was a stray magnetic field, it would shift the entire trace in one direction only, and it's probably got a MuMetal magnetic shield.

Second myth: A 60MHz CRT isn't going to have a post deflection mesh accelerator, they're only found in scopes with high bandwidth CRTs 400MHz and above.

It's a 60MHz scope tube NOT a magneitically deflected colour CRT with a shadow mask.

It looks a lot like some interaction between the X and Y amplifiers for some reason. I don't have a 2211 service manual so I can't look up the CRT part of the schematic. Many scope CRTs have a slotted acceleration electrode between the Y and X plates, Y electrodes are first in the beam path followed by slotted accelerator/screen electrode and then the X plates. If your CRT has this extra electrode between the Y and X plates check that it isn't floating. Check for dry joints on the CRT connector board.

Good luck



 

[dom0]

The 2211 operator's manual specifies a 12.6 kV nominal acceleration voltage, so the tube does indeed possess PDA.

On scopes without PDA and only the cathode voltage -1500 .. -3000 V or so accelerating the beam it is so "soft" that it is deflected by a finger held in front of the graticule

[N2IXK]

Yes, the tube definitely has a PDA.   No scan expansion lens/mesh or microchannel plate which are the features only found on high writing rate CRTs.  Perhaps the other poster was confused?

[MarkL]

This is not an electrical problem.  The CRT has very likely been damaged internally during shipping.

Regardless of the cause, the display is definitely "not as described".  I would ask for a return and refund.

[Cubdriver]

It doesn't look like a sweep issue to me - note how the lines of the wave are curving back on themselves in the distorted spots.  Unless the sweep waveform has some very limited areas where it's changing slope smoothly and repeatedly, and ONLY when the beam happens to be deflected vertically towards those spots it's either something near the face of the CRT that's badly magnetized and causing the distortion or, more likely, internal structural damage to the tube caused during shipment.

-Pat

[grumpydoc]

+1 for the suggestion that the CRT is damaged.

IF the 'scope you have is definitely the one in the first photo then the damage occurred in transit, bummer for the seller but a clear case where you should be able to return it.

If it is possible it's a different one then the seller might be being dishonest.

Either way looks like its time to send it back.

EDIT: Ok the ebay auction was not difficult to find, there is not much to go on but the mark on the bezel just under the timebase readout looks the same. There was gunk above the focus control in the photo on ebay but not on yours - assuming that you cleaned it off it appears to be the same 'scope - how was it packed?

[PaulAm]

That could be CRT damage, although I haven't seen anything quite like that.   Sometimes a severe shock will cause the deflection plates to shift without breaking the CRT.  This can shift the beam or cause a shadow.  That looks like someone bent a deflection plate into some bizarre geometry.  There might be something very strange going on with the deflection circuitry.

In any case, it's definitely time to send it back. unless it was sold as-is/for parts etc.  Then you're out of luck and it's time to open it up and see what's going on.

If you do, don't position the scope screen down.  If there are any broken glass supports, the fragments will scratch the phosphor on the screen if you do that.

[GAD]

Thanks all. It will likely go back. I'm bummed because I did manage to fix the original issue of it scanning off the screen which means it would have been perfect if not for what appears to be shipping damage. It also seems to function fine otherwise. Oh well.

[cdev]

I have a working 2211, if there is anything I can measure for you, etc. PM me.

I like it a lot.

[GAD]

I have a working 2211, if there is anything I can measure for you, etc. PM me.

I like it a lot.

Thanks, but at this point I think I'm resigned to the idea that it needs a new tube. I did manage to dial it in. It was pretty easy to do. You can see that though the distortion is still there, the information on the bottom is now where it should be.




Controls that I used:




I will say that in the short time I had this scope that I really learned to like it and I'll likely get another analog scope.

[GAD]

Out of curiosity, if I could score a new tube, is it difficult to replace? Physically it doesn't look that complicated, but would the scope require recalibration with a new tube?