Tek 2211 CRT Weirdness - Page 1
Forum section: electronics / repair

author: GAD
author_rank: Regular Contributor
timestamp: January 14, 2016, 05:58:51 am
content: 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?

author: ataradov
author_rank: Super Contributor
timestamp: January 14, 2016, 06:27:17 am
content: 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

author: GAD
author_rank: Regular Contributor
timestamp: January 14, 2016, 06:56:07 am
content: 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.

author: GAD
author_rank: Regular Contributor
timestamp: January 14, 2016, 07:13:57 am
content: 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.

author: ataradov
author_rank: Super Contributor
timestamp: January 14, 2016, 07:18:22 am
content: Quote from: GAD on January 14, 2016, 07:13:57 amYou 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

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2016, 07:21:11 am
content: Quote from: GAD on January 14, 2016, 05:58:51 amhttp://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: GAD
author_rank: Regular Contributor
timestamp: January 14, 2016, 07:32:31 am
content: Quote from: tautech on January 14, 2016, 07:21:11 amI found that. Great read!

author: GAD
author_rank: Regular Contributor
timestamp: January 14, 2016, 07:37:32 am
content: Quote from: ataradov on January 14, 2016, 07:18:22 amGrumble.

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2016, 08:09:16 am
content: Quote from: GAD on January 14, 2016, 07:37:32 amNever 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.

author: ataradov
author_rank: Super Contributor
timestamp: January 14, 2016, 08:13:36 am
content: Quote from: tautech on January 14, 2016, 08:09:16 amI never seen a CRO that needed degaussingI 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.

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2016, 08:25:02 am
content: Quote from: tautech on January 14, 2016, 08:09:16 amFrom the sweep generator to the CRT final output stages.Of course you'll need another scope to do so.

author: GreyWoolfe
author_rank: Unknown
timestamp: January 14, 2016, 12:51:10 pm
content: I have, in the past, degaussed 27" TVs with a Weller soldering gun. Worked great.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 14, 2016, 04:46:34 pm
content: 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...

author: dom0
author_rank: Super Contributor
timestamp: January 14, 2016, 05:25:23 pm
content: 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 ofinternal CRT damage by dropped parcel.

author: chris_leyson
author_rank: Super Contributor
timestamp: January 14, 2016, 07:46:55 pm
content: 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

author: dom0
author_rank: Super Contributor
timestamp: January 14, 2016, 08:33:52 pm
content: 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

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 15, 2016, 01:54:25 am
content: 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?

author: MarkL
author_rank: Unknown
timestamp: January 15, 2016, 08:24:27 pm
content: 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.

author: Cubdriver
author_rank: Unknown
timestamp: January 15, 2016, 10:28:49 pm
content: 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

author: grumpydoc
author_rank: Super Contributor
timestamp: January 15, 2016, 10:46:11 pm
content: +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?

author: PaulAm
author_rank: Frequent Contributor
timestamp: January 16, 2016, 12:27:50 am
content: 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.

author: GAD
author_rank: Regular Contributor
timestamp: January 16, 2016, 01:15:20 am
content: 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.

author: cdev
author_rank: Super Contributor
timestamp: January 16, 2016, 05:04:40 am
content: I have a working 2211, if there is anything I can measure for you, etc. PM me.I like it a lot.

author: GAD
author_rank: Regular Contributor
timestamp: January 16, 2016, 07:16:07 am
content: Quote from: cdev on January 16, 2016, 05:04:40 amThanks, 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.

author: GAD
author_rank: Regular Contributor
timestamp: January 16, 2016, 08:00:58 pm
content: 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?

author: cdev
author_rank: Super Contributor
timestamp: January 16, 2016, 08:07:23 pm
content: Its nice and sharp, and bright. It may be some simple thing. But ......Since you just bought it, I would send it back, though. **Make sure you dont negotiate outside of the ebay system** and make sure ebay pays postage, also photograph everything and box it up better than it came to you, box it up in a much better box. Make sure its return receipt, etc.Item not as represented. Or whatever its called.I think some unscrupulous ebay people often send out stuff they know is broken hoping that the person who gets it will accept it or screw up in some way and end up having to eat the cost.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 16, 2016, 08:19:36 pm
content: Quote from: GAD on January 16, 2016, 08:00:58 pmScopes are not really precision instruments, at least not better than your eyesyou won't touch the timebase replacing the tube so that will be ok, all it maybe needs is amplitude and centering, not a difficult job.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 16, 2016, 10:37:55 pm
content: Replacing a CRT is fairly easy. The only touchy part is if the tube has deflection plate connections to pins out the side of the neck. These are VERY fragile, and need to be handled with care. You also need to discharge the HV supplies before handling the tube base contacts or the PDA lead (which is usually a plug in connection on a flying lead). X and Y gain might need minor tweaking, as will astigmatism and cutoff/focus/bias.I can't find a 2211 parts list online anywhere, so I can't give you a tektronix p/n for the tube to search for. Look for a tag on the tube with a number that starts with 154-xxxx-xx. Any given scope model might use 3-4 different parts numbers as various optional phosphors were often available. Yours looks like standard P31.Sphere Research has a lot of NOS Tek CRTs available:http://www.sphere.bc.ca/test/tek-crts.html