Re: [ukvac] TECH: Asteroids - LONG
dude..
i had a very similar problem to you when fixing Jim Watt's Asteroids deluxe
board.
......and i wrote a good log about it
Asteroids deluxe JIM01:
VR4 (7815 regulator) had a broken leg that was soldered up, but
kept breaking, so i replaced that.
Game plays blind, no vector output from X, Y, or Z. Vector state
machine is fine, DACs appear to be outputting properly. When looking
at the SHCON signal on the mc14016's at locations B12 and D12, the
waveform is greatly mishapen. From reading the schematics, SHCON
is supposed to swing from -8.2v to +8.2v. I scoped the signal on my
good board and sure enough, this has a uniformed wave swinging as the
schematics suggest. On this board it is not only mishapen, but also
only swinging from -2v to +3v and is mis-shapen. The signal is
created from the CPU area, a 3mhz clock signal and something else..
This signal was ok at its TTL voltage levels, but when it was bumped up
to the +/- 8.2v, it got skewed. Looking at the +/- 8.2v supply for
these transistors, a zener diode at CR12 was only measuring +3v across
it. I replaced the diode with no difference. I found that the MC14016
at B12 was bad, and seemed to be holding the voltage down? replaced B12
and the +8.2v came back. The SHCON signal stil doesn't swing all the way
in the + range, it reads to about -7v, but still only peaks at 3v.
I replaced Q11 (2n3906) and that seems to have restored the SHCON signal
back to what it should be. I thought that the TL082 at A12 might have
had summat up with it as its output was dead, so i replaced it, no change.
I then realise that the output from both DAC's must be shafted. I popped
a good DAC on top of the X DAC at C/D11 and the picture extended properly
along the X axis. So i whipped it out and replaced it. X now seems
to look fine. I popped a good DAC over the Y DAC at A/B11 and saw the
screen extend out properly. So i whipped it out and replaced it. The
picture now extends the correct height, but the letters and graphihcs
'step up' diagonally.. I looked at the x/y position counters and after much
fiddling around, i noticed that pin 5 of F9 was LO constantly.. E,F,H,J 9
were all LO too, on the schemtics, this is DVY10, this controls the up/down
counting of the 191's.. and sure enough according to the chip specs when the
U/D (up/down) input is LO, the counter only counts up.. the lettering is
stepping diagonally up, so this now makes sense.. now to find out why DVY10
is stuck LO. found that the signal originates from the LS273 at F6, sure
enough, DVY10 was LO. I popped a good 273 on top of it and powered up,
WOO!! all working nicely.. so i clipped out the old one, installed the new
one, and then we were back to how it was before.. hmm something might be
holding it down, but the piggybacked dual 273 might have been enough to push
the signal up. I lifted pin 16 of the 273 out of the socket anyway just to
check it hadn't died on the install.. it was blinking fine, something was
definately holding it down, one of the 191's for sure, so i went along
clipping the legs of the 3x 191's that DVY10 feeds. J9 checked out ok, H9
checked out ok, but F9 which was already socketed seemed like it was the
problem child.. When i replaced the Fairchild ls191 (which appeard to work
fine in another board) with an SGS-Thompson ls191 it started working!!
FIXED
14.7.01
hope it helps..
Andy
> I've been struggling with the Asteroids board for over a week now, but I
> think I am close to fixing it. If you remeber I had a problem in the
video
> output circuit. All voltages are present and correct. I've also replaced
> the TL082s and the 4016Bs. I no longer get a postage stamp sized image,
> it's more of a large dot now! Using the scope I can get a Asteroids
picture
> before the 4016Bs but not after.
>
> Anyway, using a working Asteroids board as a reference I've tracked the
> problem down the the SHCON signal coming into the 4016Bs. I get a 3Mhz
wave
> on the working board and a rather strange looking signal on the none
working
> board.
>
> Tracing this signal from the Vector Generator Circuit into the Video
Output
> circuit at R114. On both boards I get a 1Mhz square wave (3v point to
> point) on the Vector Gen side. On the working board I get the same signal
> (reduced to 1.5v point to point). But on the non-working board the signal
> has been lost. Something is killing the signal. I don't believe the
> problem is the R114 as this reads fine on a meter.
>
> Now there seem to be several components between R114 and pin 12 of the
> 4016Bs. The Atari schematics I have don't show any of these. I guess one
of
> these could be at fault or it could be the capacitor (of unkown value) in
> parallel with the R114. But without component level schematics it's
> difficult to continue the diagnostics.
>
> Does anyone have any idea what could be causing this? Alternatively
anyone
> have any schematics that show all of the components in this part of the
> circuit?
>
> Cheers,
> Steve
>
>
>
>
>
> >From: "Steve M" <
dude..
i had a very similar problem to you when fixing Jim Watt's Asteroids deluxe
board.
......and i wrote a good log about it
Asteroids deluxe JIM01:
VR4 (7815 regulator) had a broken leg that was soldered up, but
kept breaking, so i replaced that.
Game plays blind, no vector output from X, Y, or Z. Vector state
machine is fine, DACs appear to be outputting properly. When looking
at the SHCON signal on the mc14016's at locations B12 and D12, the
waveform is greatly mishapen. From reading the schematics, SHCON
is supposed to swing from -8.2v to +8.2v. I scoped the signal on my
good board and sure enough, this has a uniformed wave swinging as the
schematics suggest. On this board it is not only mishapen, but also
only swinging from -2v to +3v and is mis-shapen. The signal is
created from the CPU area, a 3mhz clock signal and something else..
This signal was ok at its TTL voltage levels, but when it was bumped up
to the +/- 8.2v, it got skewed. Looking at the +/- 8.2v supply for
these transistors, a zener diode at CR12 was only measuring +3v across
it. I replaced the diode with no difference. I found that the MC14016
at B12 was bad, and seemed to be holding the voltage down? replaced B12
and the +8.2v came back. The SHCON signal stil doesn't swing all the way
in the + range, it reads to about -7v, but still only peaks at 3v.
I replaced Q11 (2n3906) and that seems to have restored the SHCON signal
back to what it should be. I thought that the TL082 at A12 might have
had summat up with it as its output was dead, so i replaced it, no change.
I then realise that the output from both DAC's must be shafted. I popped
a good DAC on top of the X DAC at C/D11 and the picture extended properly
along the X axis. So i whipped it out and replaced it. X now seems
to look fine. I popped a good DAC over the Y DAC at A/B11 and saw the
screen extend out properly. So i whipped it out and replaced it. The
picture now extends the correct height, but the letters and graphihcs
'step up' diagonally.. I looked at the x/y position counters and after much
fiddling around, i noticed that pin 5 of F9 was LO constantly.. E,F,H,J 9
were all LO too, on the schemtics, this is DVY10, this controls the up/down
counting of the 191's.. and sure enough according to the chip specs when the
U/D (up/down) input is LO, the counter only counts up.. the lettering is
stepping diagonally up, so this now makes sense.. now to find out why DVY10
is stuck LO. found that the signal originates from the LS273 at F6, sure
enough, DVY10 was LO. I popped a good 273 on top of it and powered up,
WOO!! all working nicely.. so i clipped out the old one, installed the new
one, and then we were back to how it was before.. hmm something might be
holding it down, but the piggybacked dual 273 might have been enough to push
the signal up. I lifted pin 16 of the 273 out of the socket anyway just to
check it hadn't died on the install.. it was blinking fine, something was
definately holding it down, one of the 191's for sure, so i went along
clipping the legs of the 3x 191's that DVY10 feeds. J9 checked out ok, H9
checked out ok, but F9 which was already socketed seemed like it was the
problem child.. When i replaced the Fairchild ls191 (which appeard to work
fine in another board) with an SGS-Thompson ls191 it started working!!
FIXED
14.7.01
hope it helps..
Andy
> I've been struggling with the Asteroids board for over a week now, but I
> think I am close to fixing it. If you remeber I had a problem in the
video
> output circuit. All voltages are present and correct. I've also replaced
> the TL082s and the 4016Bs. I no longer get a postage stamp sized image,
> it's more of a large dot now! Using the scope I can get a Asteroids
picture
> before the 4016Bs but not after.
>
> Anyway, using a working Asteroids board as a reference I've tracked the
> problem down the the SHCON signal coming into the 4016Bs. I get a 3Mhz
wave
> on the working board and a rather strange looking signal on the none
working
> board.
>
> Tracing this signal from the Vector Generator Circuit into the Video
Output
> circuit at R114. On both boards I get a 1Mhz square wave (3v point to
> point) on the Vector Gen side. On the working board I get the same signal
> (reduced to 1.5v point to point). But on the non-working board the signal
> has been lost. Something is killing the signal. I don't believe the
> problem is the R114 as this reads fine on a meter.
>
> Now there seem to be several components between R114 and pin 12 of the
> 4016Bs. The Atari schematics I have don't show any of these. I guess one
of
> these could be at fault or it could be the capacitor (of unkown value) in
> parallel with the R114. But without component level schematics it's
> difficult to continue the diagnostics.
>
> Does anyone have any idea what could be causing this? Alternatively
anyone
> have any schematics that show all of the components in this part of the
> circuit?
>
> Cheers,
> Steve
>
>
>
>
>
> >From: "Steve M" <