Tektronix 2215A worth repair?

A screenshot would be useful, if it worked ok previously and hasn't been physically dropped/damaged its unlikely the CRT would suddenly develop a distortion, although your description sounds like a duff tube. JC

Always start with the power supply.

Mark Z.

"Geoff"

... Phil

I would suspect something in the flyback suppression/blanking area

"Mark Zacharias" wrote in news:4eb9ea1f$0$28552$ snipped-for-privacy@newsreader.readnews.com:

some CRTs had tiny magnets (0.1" dia.) glued on at the factory,for beam alignment. one could have come loose.

Yes,PS filter caps,and other decoupling caps on the boards are a problem in aging scopes.

to check tube geometry,input a 6 div high signal with a fast rise time(like a square wave or time marks),one cycle per division,and turn up intensity to see the fast rise. if the tube is bad,you'll see distorted lines. the distortion remains in the same place as you move trace position controls.

IMO,2215-series are good scopes,easy to repair. I have a 2213,one that I built myself from boards discarded by other techs. Scored a second-grade CRT from the head of CRT mfg,bought the little bits I needed to finish the scope for about $20.

good analog scopes are hard to find these days.

I don't know this scope but used to work on another manufacturer's models. On one in particular, you could sometimes see this fault - it got worse as the y shift was changed. As I recall, the problem was timebase ripple (after flyback) on the supply to one of the tube accelerating electrodes. The effect was more noticable as the beam was moved (y shift) nearer to the electrode. You would need a second scope to probe the tube pins to confirm this.

"Phil Allison" wrote in news: snipped-for-privacy@mid.individual.net:

I took the case off and no difference, your implied suggestion that a change in magnetic field caused this matches what I observe, ie no electronic settings change the waveform, it looks like when someone shoves a magnet near a crt. I have not removed the tube screen but I have shaken it and nothing like a magnet bouncing around can be heard, I may just give up now, it is not a paying job just an old CRO we use occasionally for R&D work, we have newer better ones around including tek analog CRO's.

"Geoff"

There must be a chance the steel mesh has become magnetised.

Suggest you play around with a small magnet near the tube face and see what happens.

FYI:

There is a fine steel mesh just behind the face of the tube that has final acceleration voltage applied to it - if you de-focus the beam you can usually see the pattern of the mesh projected onto the phosphor.

... Phil

at

Use a degaussing coil like you use on a color CRT TV set!!

"Phil Allison" wrote in news: snipped-for-privacy@mid.individual.net:

Links below for pics taken with webcam. Mesh is visible. I have played around with a magnet, can get trace to wobble around as expected but it comes back to the same position once magnet removed. This is true for the unshielded part behind screen and the conical tube shield. I will try a degausser once I find or make one

If the distortion stays constant with the traces as they move up the screen its not the CRT

If the distortion is fixed in that area of the CRT then the CRT is internally damaged.

Magnets and deguassers will not cure this.

IMO its a broken CRT

JC