Zorba owners/Help diagnosing display issues

[Bill Degnan]

I suppose the first thing you need is the schematics for the Zorba, anyone
have this?

Do you have a volt meter with an ESR setting?  There are caps in the
display controller board, but not too many that often are used to control
the wobble and hotiz/vert behind the potentiometers.  Start with an
inspection of these caps.  You should test them and replace the bad ones.
Also test caps near the voltage regulators and coming from the main power
connector.  It's a bit of a shotgun approach, but if you test after each
change you might get lucky and the display will stabilize without having to
make too many repairs.  You could stop at that point until something
happens again.  Keep a record of which caps you replaced.    It could be
something other than a cap.   voltage regulators go too, but as you
describe the symptoms I would bet there is a bad cap in the display
controller board.

If the system does not work at all it could be a power supply problem.

Bill

On Tue, Nov 2, 2021 at 6:22 PM Ben McAllister via cctalk <
cctalk at classiccmp.org> wrote:

> Hello from Seattle everyone,
>
> I'm new to the list. I recently bought a Zorba on Ebay, which was my first
> machine as a kid back in 1985, dialing into BBSs and learning assembly and
> basic. I put a lot of hours in on this machine and was very excited to
> acquire one, even though the sale was 'as is'.  I have some issues to
> address, beginning with perhaps a faulty component on the video board
> driving the crt.
>
> While I'm an experienced programmer and have some rudimentary skills with
> electronics, I'm going to be in bootcamp troubleshooting this board. I have
> some help in my network of friends, but wanted to throw this out to the
> list.  Are there any Zorba owners who would be willing to trade
> notes/advice with me on their experiences troubleshooting hardware issues
> (or anyone else out there, for that matter :) )?  Have you used the
> composite video out to feed another monitor?
>
> Detail on my first issue: the display appears to need the kind of
> stabilization I _thought_ the horizontal and vertical hold adjustments
> would provide, but it's not entirely stable. I have tried the composite
> out, feeding it to a cheap composite->HDMI adapter, but that signal looks
> like a blank screen in need of vert/horiz hold adjusting.  Before I go much
> further, I was hoping someone out there might be able to verify their use
> of the composite out to an external display. I haven't found any detail on
> what that signal should look like, other than it's 'composite' - maybe
> someone with more expertise can tell me what assumptions I can make about a
> composite signal.
>
> Thanks for reading that long message - and glad to be a new member of the
> list.
> Ben
>