[Test-Equipment] Tektronix 475 with problems

[d8lars@dtek.chalmers.se]

Hi!

I have a Tektronix 475 that behaves oddly. Everything works quite
good, nice traces and so on, perhaps a bit wide trace one the lower
voltage ranges. The problem is that from time to time the trace become
unfocused vertically. I.e. it is not the same as if you unfocus with the
focus pot., it is only unfocused vertically, horizontally it is OK.
This happen every now and then, say one to three times per 5 min, and
is a couple of seconds to some 10-15 seconds long. The unfocusness is
abut 1.5-2 squares high. It doesn't seem to matter what voltage range
I use, and what channel I use, I can not see any difference with different
time bases either.

What could be wrong? Any seen this behavior before? Could it be bad
electrolytes. Something bad in the vertical circuits after the input
amplifiers, and if so, what? Any ideas?

/Lars

-- 
Lars E Pettersson        |  Chalmers University of Technology
d8lars@dtek.chalmers.se  |  Gothenburg, SWEDEN