G08 custom chip - interesting

Hi all,

Well, I'm *really* interested in finding a solution for bad G08 deflection
board custom chips, so I did some experimenting this evening...

The symptoms of the board are that the Y deflection likes to sit at the max
voltage output to the coil(+60VDC). All the rest of the Y circuit has been
confirmed fine.

Turns out that in my particular case, I have a chip whose Y analog input
(pin 11) says "screw the Y input!"...basically something internally has gone
haywire. As soon as you connect the Y input to it, the Y circuit output
(pin 18) goes to like 5.68VDC and stays there, which of course the Y circuit
doesn't really like. And even though the Y input likes to be +/-3VDC, pin
11 stays around -5VDC when connected.

So I bent pin 11 out of the socket to take measurements on it and found that
it was at -7VDC. Just for fun, I measured the output at pin 18...and it was
moving! So I measured the outputs to the deflection transistors...and they
looked halfway decent. So I hooked up the deflection transistors (no yoke
connected all this time) and read the outputs to the Y yoke...and they
looked halfway decent, too.

So I took a chance and hooked up the yoke and got this:

http://www.enteract.com/~jenison/pics/badchip.jpg

As you can see, the picture is sort of key stoned, compressed at the right
side, and slightly rotated to the left (if you look at the pic, you can see
the right side of the chassis for a vertical reference point).

Ok, so the picture is no where near optimal, but it's better than nothing!

Plus, if gives me a little insight as to how the chip works and what inputs
do what. At least I have a test monitor again :-)

--
Mark Jenison
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