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Tektronix 2215A worth repair?

G

Geoff

Jan 1, 1970
0
I have a tek 2215A CRO with following fault..
Left side of trace has a ripple, about 1/2 division vert
amplitude and about 25% of horizontal is affected.
Both channels the same
When vert offset is manually swept, the pattern of ripple
changes, still both channels the same
Timebase does not change shape or size of ripple
ripple is 1/2 or 1 cycle but is like someone has put a magnet on
the side of the tube.
Changing attenuator makes no difference.
Was OK a few months ago when last used

If this is a tube fault, I will junk it, what do others think?
 
A

Archon

Jan 1, 1970
0
I have a tek 2215A CRO with following fault..
Left side of trace has a ripple, about 1/2 division vert
amplitude and about 25% of horizontal is affected.
Both channels the same
When vert offset is manually swept, the pattern of ripple
changes, still both channels the same
Timebase does not change shape or size of ripple
ripple is 1/2 or 1 cycle but is like someone has put a magnet on
the side of the tube.
Changing attenuator makes no difference.
Was OK a few months ago when last used

If this is a tube fault, I will junk it, what do others think?
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
 
M

Mark Zacharias

Jan 1, 1970
0
Geoff said:
I have a tek 2215A CRO with following fault..
Left side of trace has a ripple, about 1/2 division vert
amplitude and about 25% of horizontal is affected.
Both channels the same
When vert offset is manually swept, the pattern of ripple
changes, still both channels the same
Timebase does not change shape or size of ripple
ripple is 1/2 or 1 cycle but is like someone has put a magnet on
the side of the tube.
Changing attenuator makes no difference.
Was OK a few months ago when last used

If this is a tube fault, I will junk it, what do others think?


Always start with the power supply.

Mark Z.
 
P

Phil Allison

Jan 1, 1970
0
"Geoff"
Left side of trace has a ripple, about 1/2 division vert
amplitude and about 25% of horizontal is affected.
Both channels the same
When vert offset is manually swept, the pattern of ripple
changes, still both channels the same
Timebase does not change shape or size of ripple
ripple is 1/2 or 1 cycle but is like someone has put a magnet on
the side of the tube.


** Could the case be magnetised in one area ?




.... Phil
 
N

N_Cook

Jan 1, 1970
0
Geoff said:
I have a tek 2215A CRO with following fault..
Left side of trace has a ripple, about 1/2 division vert
amplitude and about 25% of horizontal is affected.
Both channels the same
When vert offset is manually swept, the pattern of ripple
changes, still both channels the same
Timebase does not change shape or size of ripple
ripple is 1/2 or 1 cycle but is like someone has put a magnet on
the side of the tube.
Changing attenuator makes no difference.
Was OK a few months ago when last used

If this is a tube fault, I will junk it, what do others think?


I would suspect something in the flyback suppression/blanking area
 
G

Geo

Jan 1, 1970
0
I have a tek 2215A CRO with following fault..
Left side of trace has a ripple, about 1/2 division vert
amplitude and about 25% of horizontal is affected.
Both channels the same
When vert offset is manually swept, the pattern of ripple
changes, still both channels the same

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.
 
G

Geoff

Jan 1, 1970
0
"Geoff"


** Could the case be magnetised in one area ?




... Phil

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.
 
P

Phil Allison

Jan 1, 1970
0
"Geoff"
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,


** The CRT is a *mesh PDA* type - right ?

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
 
G

Geoff

Jan 1, 1970
0
"Geoff"



** The CRT is a *mesh PDA* type - right ?

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

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

http://i251.photobucket.com/albums/gg302/triode101/focus_limit
_ccw1.jpg

http://i251.photobucket.com/albums/gg302/triode101/focus_limit
_cw1.jpg

http://i251.photobucket.com/albums/gg302/triode101/focus_limit
_ccw2.jpg

http://i251.photobucket.com/albums/gg302/triode101/2215a.jpg

http://i251.photobucket.com/albums/gg302/triode101/2215b.jpg
 
A

Archon

Jan 1, 1970
0
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

http://i251.photobucket.com/albums/gg302/triode101/focus_limit
_ccw1.jpg

http://i251.photobucket.com/albums/gg302/triode101/focus_limit
_cw1.jpg

http://i251.photobucket.com/albums/gg302/triode101/focus_limit
_ccw2.jpg

http://i251.photobucket.com/albums/gg302/triode101/2215a.jpg

http://i251.photobucket.com/albums/gg302/triode101/2215b.jpg

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
 
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