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From: grr@cbm.UUCP (George Robbins)
Newsgroups: net.micro.amiga
Subject: Re: High res tubes and SMOKE
Message-ID: <33@cbm.UUCP>
Date: Sat, 22-Mar-86 18:20:05 EST
Article-I.D.: cbm.33
Posted: Sat Mar 22 18:20:05 1986
Date-Received: Tue, 25-Mar-86 02:52:51 EST
References: <26600027@ccvaxa>
Organization: Commodore Engineering, West Chester, PA
Lines: 41

> I have some graphic tubes here at work and I was going to hook them up to my 
> Amiga using the RGB outputs (I already have a VT240 head hooked up and
> working with no problems.)  I hooked up the RGB connectors and then the 
> composite sync.  I was trying not to have to use the h+v sync separately, but
> I later determined that it was needed.
> (FYI the connections were properly made)

Be warned that the horizontal and vertical sync outputs are not intended to
drive a monitor directly (for genlock only).  Too much load on them and your
machine will stop working - no smoke though...

> ...as soon as I had turned on my machine, I
> smelled smoke! I turned off the machine, took off the cover (my machine is 
> out of warranty by a few months) and inspected it.  After looking at all the
> components and seeing nothing burnt, I decided to plug it back in and watch
> for the fire.  Well, nothing smoked again, but...

Sounds like it might be some kind of grounding problem - check between the
system and the monitor to make sure that theres no AC voltage between the
grounds...

> Another question is does anyone know which chips, caps, resistors, and
> inductors make up the filtering for the video?  I don't want to have to
> reverse engineer the board.  I will be using the scope and looking at the
> signals in the mean time.

Some HC244's buffer the chip outputs and feed into a D-A resisitor network -
this goes into the three big transistors which drive the outputs through more
resistors with a takeoff of the composite video chip (MC1377).

Shouldn't be too hard to trace, check resistors, caps and transistor with a
meter first - also try composite video output to see if you lost a color in
that chip...


> Mikel Matthews Gould Computer Systems Division, Urbana, IL
> inhp4!uiucdcs!ccvaxa!mikel mikel@gswd-vms
-- 
George Robbins - now working with,	uucp: {ihnp4|seismo|caip}!cbm!grr
but no way officially representing	arpa: cbm!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)