SW X-Y output trouble (long)

Hi all

I am having trouble with a SW upright (WG monitor). I have recapped and
installed LV2000 unit and all was semi ok for an hour or so. By this I mean
some vectors were dropping out and the trench run was a bit dodgy (no
forward motion and frozen sprites).

I went to power the unit up the following day and all I got was a reduced
picture size orientated in the lower right of the monitor and lots of small
horizontal lines (all colours present) roughly in proportion to what should
have been there I.e. high scores etc

I have posted before re this problem and since then have got my hands on a
2nd hand scope, schematics etc and am a little wiser as to where things
happen on the boards etc.

I have set my scope to XY and have practically recreated the crap on the
game screen on the scope, with the addition of what I believe to be retrace
lines possibly proving that at this stage the monitor is not at fault?

I feel sure the monitor is ok as all components check out ok. I don't know
how to check the CRT though?

I have used the trouble shooting guide by J M Askey (many thanks) and I am
unable to recreate any of the wave forms within the document pertinent to
the XY outputs etc, and I am unsure what the wave forms I am reading now
mean I.e if not correct display then where to look next?

So what I thought I would do is take some readings when the display is
static .I.e. self test mode with the Hatches and Squares and in attract mode
(as a control) and this is what I have found:-

(please excuse my terminology as my electronic skills are limited)
(All readings are P-P unless otherwise stated)

In attract mode:

X output - approx 10v stable signal little fluctuation between wave forms
and separate signatures, signatures present have very steep gradients.
Y output - approx 6v signals not stable constantly fluctuating with some
signals disappearing altogether and then reappearing.

Comments: I appreciate that signals will come and go as new graphics are
drawn (scrolling scores etc) does this mean that the more static X output
could be at fault?

In cross hatch mode:

X output - Approx 10v with a block type wave form above with a 7ms duration
between blocks is 18ms. Within the blocks there are three troughs that drop
below the 0 line by 4.5v the first is at the beginning of the cycle the 2nd
is @ 1.5ms and the 3rd @ 4.5ms

Y output - Approx 6v this time the wave is a saw tooth wave form with 7
parts to it. The first has the top chopped off with the remainder all at
different sizes and durations.

Comments: The duration of these forms are identical when viewed together on
the scope I.e. they both start and finish at exactly the same times?

In square mode:

X output - Aprox 2.5v this wave appear like a block wave form but has
troughs within that extend down to the 0 line. no wave forms pass below the
0 line though?The total duration of this entire signal is 15ms with aprox
10ms gap between wave forms or next cycle (if cycle is the right word).

Y output - Aprox 8v with the first part of the wave @-8v there are then 7
wave forms that decrees in size uniformly until 0v is the inverse then
happens with them increasing above the 0 line with a further 16 equidistant
peaks and troughs (saw tooth) which are identical in duration and magnitude.
The total duration of this entire signal is 15ms with aprox 10ms gap between
wave forms or next cycle (if cycle is the right word).

Comments: I would have expected these wave forms to look identical as they
are, IMHO, only creating lines that intersect to create squares? Looking at
the wave forms how X appears to be a block wave and Y appears to be a saw
tooth I would say one of them is definitely not right?

I apologise for the length of this mail but with the little knowledge I have
I feel that I can do little more than to present my findings and hope for a
little guidance form those who know better.

Is there an FAQ available on the web re Vector games?

I look forward to your response, many thanks for reading.

Biff

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Received on Sun May 20 11:37:02 2001