Hi David,
You have a low emission CRT. Most HP CRT's are on RF instruments
where the operator feels inclined to leave the instrument on 24/7 to
keep it warmed up and stable for use at a moment's notice. This wears
out the cathode in the CRT's gun assembly, and makes it become increasingly
dim, and blurry.
There are only two fixes for this problem: 1) replace the CRT, something
that is becoming more and more difficult, and 2) restore/rejuvenate the
CRT, a process that sometimes extends the useful life of the CRT for a
good while.
I have restored several HP CRTS (I have never needed to do a tektronix CRT)
using my Sencore CR70 CRT restorer. The Sencore CR70, and CR7000 are about
the best that are routinely available. They were made for the television/
computer monitor repair market, but are equally applicable to scope, and
test equipment CRT's.
After you have restored/rejuvenated a CRT, you should avoid leaving the
instrument on 24/7. If you only turn it on when you need it, it will last
you for many many years. If you use it 24/7, it might last you only another
couple of thousand hours. Each additional time you restore/rejuvenate the
CRT, you get less of an improvement, and less additional life, until it
just quits.
-Chuck Harris
david_woodhead wrote:
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I have 2 of these analyzers and both demonstrate exactly the same problem - the trace intensity becomes inreasingly less visible as the trace line lengths get shorter. On screen text, consisting of short lines, is barely visible (unless I really turn up the intensity control).
Has anyone else seen this? I have posted a pic here of the signal on TP301 (Z axis output) with 0 volts being the bottom graticule. The intensity control is adjusted for a low intensity (but clearly visible) trace.
I'd appreciate hearing from anyone that might have seen this or can compare my scope trace with thiers?
David.
KM5TZ
