Help w/Tektronix 7905 Oscilloscope

[egb]

I pruchased a used, non-working 7905. Have almost everything fixed
except:

When increasing the trace brightness to an acceptable level there is a
halo present. It is not a uniform halo, but is displaced slightly up
and to the right of the trace, probably 20% brightness at normal
brightness of main trace.

The focus and astigmatism controls work properly.
Your help will be appreciated,
Thanks,
Emil

 

[egb]

Correction... Model # is 7904

 

[Dr. Anton T. Squeegee]

In article <1106758430.404787.102350@c13g2000cwb.googlegroups.com>,
eborys@martinauto.com says...

Correction... Model # is 7904

Hate to be the harbinger of bad news, but I see two possibilities
here. First, a bad CRT.

Second, it is possible that the high voltage is up too high. You
may have a defect in the HV section.

There is a mailing list dedicated to Tektronix O-scopes out of
Yahoo. Google for 'TekScopes mailing list.'

I also maintain a Tektronix-dedicated forum, in the form of a
PHPBBS install, at http://tekboard.bluefeathertech.com

Happy hunting.



--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"

 

[tekamn]

egb wrote:

Correction... Model # is 7904

Seems that your scope's tube is at the end of it's useful life.

You should check first the voltages in the LV and HV powersupplies - in
case you don't have a service manual, download one (e.g.
www.teknetelectronics.com)

hth,
Andreas

 

[egb]

Good Doctor, thank you for your comments, suggestions, and links. I
shall continue the odyssey of the $39 scope this weekend.
Emil
W9NM