Oscilloscope focus

[Cortical]

I have recently acquired a very old oscilloscope, and had just figured it all out when it went out of focus. Adjusting the focus dial works to some extent, however when turned all of the way it brings the line into much better focus (2cm wide rather than 6) however this is still so much that it is not easy to work with. Is there a simple fix, or is this a very complicated issue?
(I would love to give a model number, however I do not know my self, all I know is that it it is very simple and basic)
Thanks

[tautech]

Welcome to the forum.

Post some pics please as there'll be someone here that can identify it.
Then maybe we can find a link to a service manual so it can be fixed.

Unless you have some experience with CRO's will be bumbling in the dark so let's start like this.
PSU values need be checked before you do anything, value and ripple specs for the rails must be right before you touch anything else.
When that's all OK there's often a bias trimmer for focus and that allows you to set the focus control midway for most usage. But you need have all above correct before you touch anything.

Use the Attachments below the post window to add a pic file. Max= 1 Mb but 100-200 Kb gives plenty of detail. Resize/compress as necessary.

[Cortical]

Looking at it I see that it says OS250 on the front, and looks a lot like the OS250B image on this website:
https://www.radiomuseum.org/r/gould_adv_oscilloscope_os_250b.html
I will also attach an image.

[Specmaster]

Looking at it I see that it says OS250 on the front, and looks a lot like the OS250B image on this website:
https://www.radiomuseum.org/r/gould_adv_oscilloscope_os_250b.html
I will also attach an image.

The owners manual which also incorporates the service manual for this can be downloaded from this site https://elektrotanya.com/advance_os-250_oscilloscope_10mhz.pdf/download.html.