Re: GS Diagnostics

[dempson@actrix.gen.nz (David Empson)]

Polymorph <mike.a.stephens@gmail.com> wrote:

> On Apr 8, 8:44 am, Scott McCormack <samccorm...@gmail.com> wrote:
> > Does anyone know if the CTRL+OA+CA+Reset diagnostic test all the RAM
> > in the GS or just on the on board RAM? This test always says my GS is
> > OK but it acts sometimes like it may have a bad RAM chip someplace. I
> > can run GS/OS just fine, making RAM disks seem to be fine etc but the
> > machine just crashes with some programs for no apparent reason. It
> > doesn't do it randomly but certain applications just won't work (they
> > crash to the monitor) and I want to make sure my machine doesn't have
> > some sort of weird problem. My GS is a ROM 3 machine with a total of 3
> > MB of RAM. I think the RAM board is an Apple made one but I'll have to
> > check it and confirm as I don't have it in front of me.
> >
> > The only other problem with my GS is that I can't seem to be able to
> > use the printer port. When I try and use it as a serial port no data
> > ever seems to come across and when I attempt to use as the appletalk
> > port GS/OS locks up when I try to open the Appleshare control panel.
> > Is it possible the printer port is fried? The modem port works just
> > fine. The GS came from a school so I am sure it has had a hard life. :)
> 
> Unfortunately, the IIgs self test only tests on-board RAM. To test the
> RAM in a IIgs' RAM expansion card, you need to run a memory test
> program like BitBanger or the one found on the Appleworks IIgs Utility
> disk. You should be able to find both of these in the usual archives.
> If you can't, post back and I'll see if I can dig up one or the other.
> 
> As for the serial problem you mentioned, its odd that the modem port
> works but the printer port does not as they both use the same Zilog
> 8530 serial chip. The fact that the serial port works seems to
> indicate at least that the 8530 chip is still functioning correctly.
> Maybe there is some damage done to the printer port connector itself?
> I'm hopeful someone else here can shed some light onto why you are
> experiencing these strange symptoms.

I don't have a circuit diagram handy, but it is likely that the printer
and modem ports have separate transceiver chips, which do voltage
conversion between logic levels (0V to 5V) and the levels used on the
serial connector (-5V to +5V with an inversion stage).

It is quite possible that the printer port's output transceiver is
damaged. I'd have to refresh my memory on LocalTalk to see if that might
explain locking up when trying to do AppleTalk stuff, but it is feasible
if the driver has no timeout on a loop which is waiting for some
feedback from the network.

-- 
David Empson
dempson@actrix.gen.nz