Tips needed to repair Apple color composite monitor

From: Sam Ismail <dastar_at_ncal.verio.com>
Date: Tue Aug 25 00:21:08 1998

On Tue, 25 Aug 1998, Tony Duell wrote:

> Excellent. That means (almost certainly) that the CRT and flyback are
> fine. So the fault is likely to be fixable...
> BTW, is it the day for finding monitors? I found the original Gemini
> monitor (greenscreen) for the Galaxy 2 I got last week. It doesn't work
> yet, but I'll fix it.

These monitors are becoming increasingly easier to find, which is a good
thing because they are nice color monitors for any Apple ][ (and ///). I
got this one for $10. If I knew it wasn't working I would've left it
behind, but I plugged it in and saw video so I figured it was fine.

> OK, a problem in the video path. Now, it's composite, so there's an NTSC
> decoder, right? And it's likely to be a single chip. Look for a crystal
> (3.58MHz, most likely) and find the chip near it. Now look for data on
> that (it's probably used in TVs as well - identify who really made the
> monitor (FCC id?), and look at some Sams Photofacts or whatever).

FCC ID: BCG966A2M2056

The "A2M2056" leads me to believe this was an Apple manufactured monitor
since that is also the Apple model number for this monitor.

I'm disassembling the monitor now so I can pull the circuit board out and
get a better look. I've located a 42-pin chip (Toshiba TA7644BP) which is
most likely the decoder. I bet I have a Toshiba data book but its buried
in one of the many boxes of books.

> Now start tracing signals. Is the chip getting power? Is the video input
> getting to it? Is the oscillator running (check with a 'scope). What are
> the outputs doing? What about the video output transistors (on the CRT
> baseboard?) Do the voltages there look sensible?

Well, the VOM batteries up and died and I don't have a scope. I'll get
some batteries and check what I can and report back. Luckily I have
another one of these monitors so I have a reference for normal. I've been
looking for a nice scope at one of the many local surplus shops but so far
the ones I've found have all been gutted.

Thanks!

Sam Alternate e-mail: dastar_at_siconic.com
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Received on Tue Aug 25 1998 - 00:21:08 BST

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