Tech:Tempest Y output clipped at board

[Guest]

Archived from groups: rec.games.video.arcade.collecting (More info?)

I'm working on a Tempest set that is perplexing me.

The 'Y' output is kind of clipped or compressed in the negative
direction. It displays like this on both the monitor and on an O-scope
in X-Y mode. None of the Y channel pots do anything to change this.

I thought the outputs from the previous stages looked similar enough
to the X channel, so I replaced the final TL082CP op-amp and got no
change, so it must be something else.

I fooled around enough and zapped the 6.8V supply, so now I get no
deflection at all.

So here I am on the newsgroup.

Any pointers would be appreciated.

Kerry

 

[Guest]

Archived from groups: rec.games.video.arcade.collecting (More info?)

Maybe one of the 1495's - got any pics of the screen before you toasted out
the power?

--
-Steve P.

All messages are scanned with Norton Anti-Virus

"K.S." <kstillinger@sc.rr.com> wrote in message
news:LPupe.260$ax3.46725@twister.southeast.rr.com...
> I'm working on a Tempest set that is perplexing me.
>
> The 'Y' output is kind of clipped or compressed in the negative direction.
> It displays like this on both the monitor and on an O-scope in X-Y mode.
> None of the Y channel pots do anything to change this.
>
> I thought the outputs from the previous stages looked similar enough to
> the X channel, so I replaced the final TL082CP op-amp and got no change,
> so it must be something else.
>
> I fooled around enough and zapped the 6.8V supply, so now I get no
> deflection at all.
>
> So here I am on the newsgroup.
>
> Any pointers would be appreciated.
>
> Kerry
>

 

[Guest]

Archived from groups: rec.games.video.arcade.collecting (More info?)

> I fooled around enough and zapped the 6.8V supply, so now I get no deflection at all.

Not to state the obvious, but you should start by replacing
that zener diode. If the 6.8V is not working properly, it'll prevent
you from knowing if you've fixed the original problem. In addition
the the LM1495's that Steve mentioned, it could also be one or more
of the analog switches or earlier op-amp stages. Could be the
DAC itself, of course. It might be informative to force the game
into cocktail mode and see what happens when the screen tries
to flip. If the problem stays, then you know it's downstream of
the flip circuitry. If it follows the flip, then you know it's upstream...

Alex
----
ayeckley@elektronforge.com
www.elektronforge.com