From: ddkilzer@iastate.edu (David D Kilzer)
Subject: Re: Apple IIc acting STRANGE!
Organization: Iowa State University, Ames, IA
Date: Thu, 8 Oct 1992 02:09:57 GMT

In article <91968@netnews.upenn.edu> Bob writes:
>In <91561@netnews.upenn.edu>, kupiec@hp800.lasalle.edu writes:
>>There is a strange problem that has been occuring on my IIc for a
>>while now.  Here are the symptoms:  Sometimes the character generator in
>>the machine will go nuts distorting characters, or "snow" will appear on
>>the screen.  Other times the screen will totally flip out like someone has
>>messed with the monitor's horizontal hold.  A "hiss" can be heard when this
>>happens.
>>
>>I know that the problem *IS* with the COMPUTER!
>[...]
>>The motherboard is a Unidisk 3.5" model and not a "old" type.
>[...]
>
>OK, here is a followup on some things I forgot to mention.
>
>OA-CA-ctrl-reset says "System OK".  What does this check anyway?  RAM?  ROM?

I'm not sure what all it checks, but it at least checks RAM.  Anyone
know everything that is checked?

>There is NO Zip or other speedup chip installed.  However there is a
>No-Slot clock installed.  (sidenote:  I've had the clock for 5 years now,
>can I expect it to die soon?  If so, can I replace the battery?)

Yes, the lifetime of the battery is about 5 years (if I remember
correctly) and will probably die soon.  You can't replace the battery in
the clock; you must buy a new one (I'm not sure if SMT takes back the
dead ones for a discount or not; you'd have to check).

>Another person emailed and suggested the power supply as the problem.
>(I forget your name/address at the moment, but thanks anyway.)  This could
>be a culprit, but I have not tested it yet.  Anyone know the pinouts?

Not I.

>Which chip is responsible for character generation on the video monitor?

I can't remember the location on the //c logic board, but I know it's a
socketed chip (the socket on my board has more places for pins than does
the chip that's in it).  If you open up your //c, you should be able to
find it (although it may be hidden under the disk drive).  Just read the
printing on the chip and/or the logic board.

You said later that you ran a diagnostic on it, so I'm assuming the
character generator is okay.  

>The IIc hasn't have the symptoms in a while now, but a cure when it would
>go "nuts" was to lift the IIc about 2" and drop it.  It cured the problem
>90% of the time.  The other 10% might have required multiple drops.  This
>leads me to believe a motherboard problem more than anything else.  (I know,
>not a smart idea to drop it, but it *DID* fix the problem!)

Sounds like a loose connection somewhere...maybe in the video-out of the
//c or the video-in of the monitor.  What I would suggest doing is to
take a pair of plyers and bend the leaves of the RCA plugs on both ends
of the cord so that a tighter connection is made between the computer
and the monitor.

So if the end of your RCA plug looks like this, bend the "leaves" in a
little to make the connection tighter (please forgive the ascii
picture--it's the best I could do in 5 minutes :)

                bend in
                   \/
                _______
               /       \
            /      _      \
bend in ->  |     <_>     |  <- bend in
            \             /
               \_______/
 
                   /\
                bend in

Of course, don't bend them in TOO much...then you won't be able to get
the plugs in.  :)  This should prevent any loose connections in the
monitor cord.  If this doesn't help, then it's probably a bad connection
on the logic board of the //c or inside the monitor.

BTW, does anything happen when you wiggle the cord (at either end) when
it's plugged in and the //c is on?

>I ran a "IIc Dealer Diagnostic" disk on the IIc and all tests came up
>clean.  RAM, ROM, MMU, Char Gen, etc.
>
>Thanks for your help so far.  Maybe I will find the problem.  Please
>followup to the address below!

Dave
-- 
[   >The Davemeister<  ][     __IMZADI__  ST:TNG Novel by Peter David     ]
[ ddkilzer@iastate.edu ][ Riker (about Counsellor Troi): "She looked good ]
[   David D. Kilzer    ][   naked.  Okay, great naked.  Okay, spectacular ]
[   ~~~~~~~~~~~~~~~    ][   beyond belief naked."                         ]