Zenith Z-90 startup

[Jules Richardson]

On 05/12/2018 02:29 PM, Mister PDP wrote:
> Hello,
>
> I have had this issue with a number of H/Z89s I have. The terminal board
> and the logic board are two separate systems, so it seems to be common for
> the logic board to go down while the terminal board keeps working. I would
> check voltages on the logic board, then take it out of look for blown
> tantalum caps and burnt traces. The tantalum caps used in these systems
> seems to like to cause issues, with 5\8 of my systems experiencing issues
> with them. If that doesn't do the trick then check the power regulators on
> the logic board, as those can cause issues too.

Thanks, I'll take a look. I've actually got lots of technical docs for the 
system... schematics, firmware source listings, CP/M BIOS source listings 
etc. - Zenith seemed to be really good in that regard. If it's not somehow 
expected behavior then I'll do some digging regarding caps, voltages etc. 
and go from there.

Will reseat chips, too - when I pulled* the boards yesterday to do some 
general checks I did notice quite a bit of tarnishing on IC legs, which 
makes me wonder if some of them haven't rotted from the inside-out (as they 
sometimes do).

* What an odd setup! Nice hinged case for access to the inside, but then 
lots of unscrewing and unplugging stuff and digging around right next to 
the CRT in order to actually *do* anything. I half wonder if Zenith's 
intention wasn't to make all the boards hinge out backwards too, and then 
they found that they just couldn't quite make it work.

cheers

Jules