tempest deflection problem - voltage's OK

[Jerry]

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

I'm having a problem with a monitor in a tempest, I'd sure appreciate
any help I can get. The screen only displays the top half, with the
infamous line in the center. Looking at the outputs to the deflection
coils I see it switching between +/- 25v as expected. When I measure
the coils one is at 0.7 Ohms, the other at 1.2 Ohms.
Re: the same circuit, is the bottom 1/2 of the screen the X deflection
on the vertical mounted chassis? Is the bottom 1/2 of the screen
deflected towards by the positive or negative voltage?
Any thoughts on this?
Thanks,
Jerry

 

[Guest]

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

>The screen only displays the top half, with the
>infamous line in the center

I always found the problem on asteroids to be on the CPU (op amp), but
it could also be one of the four large transistors on the chassis of
the monitor.

Kirb

 

[Guest]

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

Sounds like a transister issue to me. Possibly a deflection but more
likely the transister. Do you know how to check them?

 

[Guest]

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

Most likely it is the chasis mount transistors or wireing/insulators for
them. Start there then move to the deflection board for troubleshooting.

G.


"Jerry" <jpl_812@yahoo.com> wrote in message
news:1122348600.419798.30580@g49g2000cwa.googlegroups.com...
> I'm having a problem with a monitor in a tempest, I'd sure appreciate
> any help I can get. The screen only displays the top half, with the
> infamous line in the center. Looking at the outputs to the deflection
> coils I see it switching between +/- 25v as expected. When I measure
> the coils one is at 0.7 Ohms, the other at 1.2 Ohms.
> Re: the same circuit, is the bottom 1/2 of the screen the X deflection
> on the vertical mounted chassis? Is the bottom 1/2 of the screen
> deflected towards by the positive or negative voltage?
> Any thoughts on this?
> Thanks,
> Jerry
>

 

[Guest]

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

>I guess the bottom line is to just shot-gun out the drivers and don't
>over think the prolem. That said, I'll probably take home a digital
>scope and capture reference waveforms for next time...

It seems that you did over think the problem and are still doing so.

This fix has been posted a ton of times because it happens all the
time. The common failure points were covered and this could have been
fixed quickly. Putting the old part back in only risked hurting more
parts.

Kirb

 

[Guest]

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

Jerry, thanks for posting the follow-up, it's always good to have a
problem/solution/result included for future searches.

You're mention of the transistor's behavior is commonly refered to as
"leaky" operation and it's very common in deflection transistors in XY
monitors.

After you work on a few of these, you'll recognize the symptoms
quickly. If you purchase cap kits from Bob Roberts, he offers a deluxe
version with the large TO-3 transistors included at a minimal increase
in price over the basic kit.

In case you haven't run across it yet, several excellent FAQ's on XY
monitors are available to download at: www.ionpool.net

Mike Doyle

 

[Jerry]

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

Thanks for the link. I've tried following it in the past, but found it
down a number of times, forgot to try again. Looks like a lot of info
there.
I'm sure I over thought this issue, and I'm sure I'll continue to do
so. I'm more interested in understanding the operation than a quick
fix. I work with digital stuff, analog is still half greek. I'm sure
I'll have plenty of opportunities to learn more about monitors.

Jerry



syncbus@gmail.com wrote:
> Jerry, thanks for posting the follow-up, it's always good to have a
> problem/solution/result included for future searches.
>
> You're mention of the transistor's behavior is commonly refered to as
> "leaky" operation and it's very common in deflection transistors in XY
> monitors.
>
> After you work on a few of these, you'll recognize the symptoms
> quickly. If you purchase cap kits from Bob Roberts, he offers a deluxe
> version with the large TO-3 transistors included at a minimal increase
> in price over the basic kit.
>
> In case you haven't run across it yet, several excellent FAQ's on XY
> monitors are available to download at: www.ionpool.net
>
> Mike Doyle

 

[Guest]

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

Jerry <jpl_812@yahoo.com> wrote:
: Just wanted to follow up on a problem I had with a tempest monitor.
: Hopefully it will help someone in the future. The monitor only
: displayed the top 1/2 of the screen. The deflection coil was being

There are flow-charts for repair of these monitors, includeing which
transistors to replace depending on which half of the screen is missing, one
of the best known is the Greg Woodcock FAQ . Google for it, read it, then
read it again.

Trust me.


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