Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!rice!uw-beaver!tektronix!percival!bucket!leonard
From: leonard@bucket.UUCP (Leonard Erickson)
Newsgroups: comp.sys.ibm.pc
Subject: Re: cga vs 286 speed (was:baby at cga)
Message-ID: <1330@bucket.UUCP>
Date: 31 Mar 89 18:45:43 GMT
References: <9191@netnews.upenn.edu>
Reply-To: leonard@bucket.UUCP (Leonard Erickson)
Distribution: usa
Organization: Rick's Home Grown Unix; Portland, OR
Lines: 28

In article <9191@netnews.upenn.edu> wist@eniac.seas.upenn.edu (Bundy Wist) writes:
<Hello          
<I have a composite monitor that I am using with a 12Mhz AT
<compatable. The problem is NO COLOR ! When I use the same
<CGA with a 10Mhz machine or when I use a RGB monitor with
<either machine there IS color; only the 12Mhz + composite
<monitor set up gives no color. My question: Do they make 
<CGA's that are made for 12Mhz machines? Can I use this CGA 
<with some sort of modification? I don't really want to invest
<any more money in the CGA format (ie buy a RGB monitor or 
<buy a $$$$$ CGA ). Thanks in advance.

I had a similar problem with a CGA card on my 10 Mhz XT clone. The CGA
needs a 3.57 Mhz colorburst frequency that it gets off of the system
bus. On turbo machines, this requires both a second crystal *and* a
trimmer capacitor. On my clone nobody had bothered to set the trimmer!

Once I tuned it, I got color with no problem. 

Either the AT doesn't *have* that signal (unlikely) or like me, you
are going to have to find the trimmer and tune the signal. Use a *plastic*
TV tuning tool, not a metal screwdriver!

-- 
Leonard Erickson		...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I'm all in favor of keeping dangerous weapons out of the hands of fools.
Let's start with typewriters." -- Solomon Short