Re: Fixed! (was: Cinematronics monitor help)

> Hi all,
>
> I've got an early version Tailgunner monitor here. I was able to borrow a
> working Star Castle machine from someone and am using it as a test fixture
> for the Tailgunner monitor.
>
> Right now, the monitor stays up for about 10 seconds, with deflection
> chatter, no picture. Then the -25V breaker pops (then shortly after, the
> +25V breaker).
>
> Measuring voltages, all regulators are outputting the correct voltages
> (+/-18VDC, +/-15VDC). However, the +25VDC seems high (about 28 volts).
> The -25VDC is right on the money. However, when the -25 pops, the +25VDC
> line dips down to +25VDC.
>
> Unplugging the yoke and retrying, the breakers do not pop, and I get a
nice
> white dot in the center of the screen.
>
> I've checked the tants, diodes and transistors; they all seem fine.

With the yoke disconnected and neck harness disconnected, I decided to take
a voltage reading across the yoke inputs. As was Zonn's suspicions, one of
the yokes was pegged to the -25VDC side. So I had it narrowed down to an
axis.

Then I tried the trick with swapping the wires that led from the
DAC/Switch/OP amp section to the deflection section. Unsoldering and
resoldering new jumper wires from near the pots location to the deflection
side, I verified that the same problem exists, and that the working side was
still good. So I had narrowed it down to one axis deflection side.

First I thought something might be breaking down and connecting the -25VDC
directly to the yoke output, so I shotgun replaced all the diodes in that
section. No change.

Then I took voltage measurements during running and changed any part where a
reading was different from the other side. That wasn't helping.

Finally, I took out my logic probe (from Radioshack, makes nice beeping
noises :-)) and decided to trace the input from the DAC side to the
deflection side. I follwed it through the 2N5210s and I could actually hear
through my logic probe, the deflection "chatter". So I followed that while
comparing to the other side occasionally, and it led me to the 2N5322 from
the 2N5210s. There the chatter stopped and was just a constant "low".

I replaced it, fired it back up, and now there was deflection chatter coming
from it!

Hooking up the yoke and the neck harness, the monitor worked! I would tell
you the part replaced, but it would be meaningless, as Cinematronics tended
to use different screening numbers for different deflection boards (which
really sucks, especially if you are trying to write a fix-it document. The
particular part is Q3 on some versions, and Q204 on others.)

Now the vectors are very wavy; shimmering a lot. I hope replacing some of
the capacitors will help, but any other advice how to stabilize the vectors
on a Cinematronics monitor would be appreciated.

One more to go...

--
Mark Jenison
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