Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Tektronix 2215A worth repair?

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?
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Default Tektronix 2215A worth repair?

On 11/8/2011 6:51 PM, Geoff wrote:
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
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Default Tektronix 2215A worth repair?

"Geoff" wrote in message
...
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.

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Default Tektronix 2215A worth repair?


"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






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Default Tektronix 2215A worth repair?

Geoff wrote in message
...
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




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Default Tektronix 2215A worth repair?

"Mark Zacharias" wrote in
.com:

"Geoff" wrote in message
...
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.


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


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.


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

Mark Z.



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.

--
Jim Yanik
jyanik
at
localnet
dot com
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Default Tektronix 2215A worth repair?

On Tue, 8 Nov 2011 23:51:53 +0000 (UTC), Geoff
wrote:

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.
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Default Tektronix 2215A worth repair?

"Phil Allison" wrote in
:


"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



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.
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Default Tektronix 2215A worth repair?


"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







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Default Tektronix 2215A worth repair?

On Nov 10, 1:31*am, "Phil Allison" wrote:
"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


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


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Default Tektronix 2215A worth repair?

"Phil Allison" wrote in
:


"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




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/g...01/focus_limit
_ccw1.jpg

http://i251.photobucket.com/albums/g...01/focus_limit
_cw1.jpg

http://i251.photobucket.com/albums/g...01/focus_limit
_ccw2.jpg

http://i251.photobucket.com/albums/g...e101/2215a.jpg

http://i251.photobucket.com/albums/g...e101/2215b.jpg
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Default Tektronix 2215A worth repair?

On 11/13/2011 8:13 PM, Geoff wrote:


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/g...01/focus_limit
_ccw1.jpg

http://i251.photobucket.com/albums/g...01/focus_limit
_cw1.jpg

http://i251.photobucket.com/albums/g...01/focus_limit
_ccw2.jpg

http://i251.photobucket.com/albums/g...e101/2215a.jpg

http://i251.photobucket.com/albums/g...e101/2215b.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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