Zorba owners/Help diagnosing display issues

[Ben McAllister]

Thanks for the advice - I have the schematic and am going to embark on the
path you mention.  Appreciate it. I’ll be posting videos of my progress on
YT, provided I make progress. :)

On Tue, Nov 2, 2021 at 4:51 PM Bill Degnan <billdegnan at gmail.com> wrote:

> 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
>>
> --
-- 
Ben McAllister | listenfaster.com |  @listenfaster | theguitarcult.com |
tuktuband.com | c: 206.849.3183