[GreenKeys] OT: Need help to T-Shoot this Tek 485 scope

[drlegendre .]

I'm officially confused. It's almost as if there's a section missing from
the 485 service manual (free on BAMA, etc). There are repeated references
to a "Transformer board A15", but it is not shown in the board ID section,
nor can I find it anywhere inside of the chassis. To make matters worse,
I'm not actually sure that the resistors in question are to be found on
that board - but the schematic does seem to indicate that's where to find
them

Tek is nice enough to group parts of the same numeric prefix in close
proximity. In this case, I need to find the board with Rs and Cs in the
1600-16XX range. If they are on that board that's tucked deep inside the
middle, that's fine and all - but I can't tell if that's correct, nor do I
know how to remove that board being that I'm unable to find the dang thing
in the docs.

It's a long doc, as you imagine. And this is my First Ever Old Tek Scope,
so obviously, I'm feeling around in the dark, here.

So just where the heck is that board, and how can I extract it?

On Tue, May 9, 2017 at 8:15 PM, drlegendre . <drlegendre at gmail.com> wrote:

> Paul,
>
> Yes, I know exactly what you're talking about and that's a very good
> suggestion. If you have the Tek 485 manual they're R1603,04,05,06,08,09. I
> think they use multiple parts as to avoid exceeding the Emax of the
> resistors, which is typically around 600V. One thing so far - I can find
> the parts on the drawing, but not on the machine. Tek says they are on
> "transformer board A15" but no such board exists, at least in the docs!
>
> But either way it's a very high-Z circuit and any kind of leakage or other
> trouble will spoil it..
>
> Now what I +really+ need to know, is what voltage should the g1 have vs.
> cathode? IIRC, I read -9V on g1, so at least it's proper in the sense that
> it is negative - but what should the actual value be? And what would I
> expect to measure with a typical (11M Zin) DVM? I mean, the overall accel.
> potential in that tube is like 21kV (18kV anode, -3kV cathode) so I'd
> expect to see a whole lot more than -9V bias, eh - or am I way off base in
> my assessment?
>
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