oscilloscope problems

B

Barry Hobbs

Guest
Hello everyone, My oscilloscope has gone wrong. Was going fine then it
suddenly went out of focus for no reason. The focus knob hardly has an
effect, its majorly out of focus


any ideas ?

many thanks!
 
Barry Hobbs wrote:
Hello everyone, My oscilloscope has gone wrong. Was going fine then it
suddenly went out of focus for no reason. The focus knob hardly has an
effect, its majorly out of focus


any ideas ?

many thanks!


Make sure it's not just HF noise that looks like defocussing.
Click to expand...

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Could be lots of things. What make/model?
Will moving the coupling selector to gnd clear it up? if so, it's
probably the leads.
If not, it could be the HV /focus circuit. Could be many things, often
it's dried out/leaky electrolytic caps.
If you leave it off for a few hours or a day, does the problem appear
immediately or does it happen after a few minutes?
I once had a cracked power resistor in the focus circuit , took a
while to find it - no fun.

On Wed, 16 Mar 2005 17:36:11 GMT, "Barry Hobbs"
<barryhobbs1@ntlworld.com> wrote:

Hello everyone, My oscilloscope has gone wrong. Was going fine then it
suddenly went out of focus for no reason. The focus knob hardly has an
effect, its majorly out of focus


any ideas ?

many thanks!
Click to expand...
 
Thanks for the replies, the model is:

Iwatsu - SS 7636 350Mhz 4 channel

Its not the leads-the whole display is like it (including the numerical
display for 'time div' etc.)

As for when it happens...it was fine until the other day, and when it was on
it suddenly went like it. ever since its been the same.

thanks!


"Asplanchna" <tiny@rotifer.com> wrote in message
news:e51h31tihmje6bdi5l1ses9c7l073qns5h@4ax.com...
Could be lots of things. What make/model?
Will moving the coupling selector to gnd clear it up? if so, it's
probably the leads.
If not, it could be the HV /focus circuit. Could be many things, often
it's dried out/leaky electrolytic caps.
If you leave it off for a few hours or a day, does the problem appear
immediately or does it happen after a few minutes?
I once had a cracked power resistor in the focus circuit , took a
while to find it - no fun.

On Wed, 16 Mar 2005 17:36:11 GMT, "Barry Hobbs"
barryhobbs1@ntlworld.com> wrote:

Hello everyone, My oscilloscope has gone wrong. Was going fine then it
suddenly went out of focus for no reason. The focus knob hardly has an
effect, its majorly out of focus


any ideas ?

many thanks!
Click to expand...
 
Sounds like it's probably the HV/focus section (never seeing an Iwatsu
myself).
Got a user or service manual with a schematic & voltage test points?
You might just get away with inspecting the electrolytics for leaking
goo/browned/stretched plastic covering & replacing them.
Check for any overheated (browned /charred) resistors, & maybe any
overheated/lifted/cracked traces on the board.
***Be very, very careful with the anode lead/HV section though!!***
If it's too expensive to fix, Ebay it like everyone else! ;-)
G'Luck!


On Wed, 16 Mar 2005 19:52:14 GMT, "Barry Hobbs"
<barryhobbs1@ntlworld.com> wrote:

Thanks for the replies, the model is:
Iwatsu - SS 7636 350Mhz 4 channel
Its not the leads-the whole display is like it (including the numerical
display for 'time div' etc.)
As for when it happens...it was fine until the other day, and when it was on
it suddenly went like it. ever since its been the same.
thanks!
Click to expand...
 
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