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HP8568B and HP8566 focus issues

Question asked by G0HZU on Oct 17, 2013
Latest reply on Jan 27, 2016 by sreaves
Hi

I have an HP8568B and a HP8566A/B and they both suffer slightly from the fuzzy graticule problem.
i.e. the main trace is nice and bright and sharp but the graticule 'comes on early' on the brightness button and by the time I have the main trace nice and clear and focussed, the graticule has gone out of focus.

I know this is a common issue and many say it is just the CRT entering old age as it can't maintain focus for long and short vectors etc. But the interesting thing is that the graticule looks lovely and sharp at a lower intensity.

So I'm left wondering if there is a way to alter the graticule intensity in the firmware or the hardware. I can turn OFF the graticule on the front panel and the 
main trace stays clear and sharp.

So does anyone know if there is a resistor or a trimmer that sets the graticule intensity level? If it is set in the firmware then maybe the firmware can be altered to turn it down a bit. The other thing is that maybe there is a component somewhere that ages and causes this imbalance between the graticule and the main trace.

Thanks in advance for any replies :)

Regards
Jeremy  

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