Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!amiga!jimm
From: jimm@amiga.UUCP (Jim Mackraz)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga 2000HD with NEC multisync II won't boot
Message-ID: <3397@amiga.UUCP>
Date: 25 Feb 89 07:16:50 GMT
References: <9577@louie.udel.EDU>
Reply-To: jimm@cloyd.UUCP (Jim Mackraz)
Organization: Commodore-Amiga Inc, Los Gatos CA
Lines: 54

In article <9577@louie.udel.EDU> Tollefson (Jon_Tollefson_) writes:
)
)I recently bought an NEC multisync II monitor.  It came with a cable for
)connecting to an IBM.  I had a local dealer wire one of the cable ends to
)plug into the Amiga.  But now the hard disk (autoboot) won't boot when the
)monitor is connected to the computer.  The monitor will flash a couple of
)times but then stay black.  The hard disk activity light doesn't appear to
)come on at all.  If either end of the cable is disconnected then it will
)boot when the computer is turned on.  After the disk has started to boot I
)can connect the video cable and the picture is fine and it completes the
)booting process with no problem.  I don't have any other extra hardware
)attached.  Has anyone else had a similar problem?  If so, what was the
)problem/solution?

You're going to need more information than I can give you, but the basic story
is this.  The NEC cable is connecting to two signals, horizontal and vertical
sync, that typically aren't used.  There function is combined on a single pin
called composite sync which is normal for common monitors.

The genlock capability of the Amiga is mainly the machine's ability to synchronize
itself with the video of an external source, such as a VCR hooked up to a genlock
adapter.  The Amiga is mistaking noise on one of the sync lines for an external
source, and deciding to let it control the timing of the machine.  This doesn't
work, of course, and the machine dies.

The trick is to install a "buffer on the sync lines" on the Amiga end of
the cable.  It's a single cheap chip, but has to be hooked up in there somehow.

This problem (and adapted cables) will soon be in abundance, since to benefit
from the new modes of the Enhanced Chip Set, you need to hook up a multi-frequency
monitor to hsync and vsync.

There is some tech note, perhaps available to dealers, which explains how
to make such an adapter.  Someday, I expect to see somebody sell adapters
for popular multi-monitors.

Perhaps someone has an online version of the description, or the address
of someone who will solder you one up.  It will probably be best marketed
as a 23-9 pin connector (or whatever is on the end of the NEC cable), so
if you hacked the end off your cable and stuck on a 23 pin, it's solderin'
time.

The test for genlock is done at boot time, in software.  If you survive
that by disconnecting, it won't check again.  Sort of drastic.  Before
we had a buffer on ours, we had a switch on (whichever) sync, which we 
kept open during boot.   hack hack hack

	jimm

-- 
Jim Mackraz, I and I Computing	   	"Like you said when we crawled down
{cbmvax,well,oliveb}!amiga!jimm          from the trees: We're in transition."
							- Gang of Four
Opinions are my own.  Comments are not to be taken as Commodore official policy.