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