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TECH: Qbert

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Anonymous
May 31, 2005 7:32:09 AM

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

OK folks, I'm on my last legs with this thing...

Picked up a nice numbers-matching Qbert, non-working, awhile back.
Turning the machine on, I would get a frozen garbage filled screen. OK...

Pull off old battery, and repair all trace corrosion by scrubbing with
vinegar, and a good hour of testing. Fine. same garbage problem. Checked
my 5 volts and I'm good at the chips. OK...

Next, replace the 8088 with another one...same problem....

Replace all the chip sockets, still the same frozen garbage problem.
Switch ram chips with no change. Ick...

Pick up one of Clay's Qbert Multigames (thanks Erik!), figuring if there
is a problem with a bad EPROM replacing it with this would work, cause
you basically replace everything rom-related....NOT!...still garbage,
but a little different. some of the garbage changes colors and even
sometimes the background changes colors. Some characters flash on and
off. Pretty, but not what I'm looking for.

The machine will say "hello I'm turned on" IF the main board is not
plugged in, but will not if it is. My PS needs a rebuild, but to get the
thing up and running, I've frankenstein'd a switcher to run the +5 to
the main PCB.

Is there anything I'm missing here? Does the main board need anything
more than +5? I don't see anything on the schematic to tell me
different. I've looked at this F@#*ing board long enough to know that
I'm going to have to get a swearing marquee for it before it's all over ;-p

Any help would be greatly appreciated. I want to get this board fixed
since it's original. Thanks!

Jeff

More about : tech qbert

Anonymous
May 31, 2005 7:33:51 AM

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

I believe there are 4 little led's on your power supply, and all 4
should be lit.

I had one with garbage for months and tried everything. Nothing ever
changed, just garbage. Changed all the fuses, fixed the power supply,
exchanged the power supply, sent the main PCB in to be checked, sent
the power supply back to be checked, changed the filter board, it just
went on and on.

Bret Pehrson helped me out a lot. You might want to check for AC
ripple.

Then I checked the fuses with a DMM and found one that was no good,
looked new. Replaced it, again, and the game now plays.

It ended up being a 10 amp fuse on the bottom panel assembly in the
cabinet.

It can really make you mad sometimes.

-Tim
Anonymous
May 31, 2005 9:48:06 AM

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

If you've got two power supplies in the game, make damned sure you've
tied the GNDs together.
Related resources
Anonymous
May 31, 2005 5:57:48 PM

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

Ditto that. For example, my sync seperator ground has to be tied to the game
ground or it won't sync-surprise. Usually that's not an issue since the
seperator is run off the switcher but the other day I was using an System I
harness on the bench to work on the System I board. Tying them together
fixed my sync issue.


"Rob Carroll" <robert.carroll30@verizon.net> wrote in message
news:1117543686.196060.23440@g47g2000cwa.googlegroups.com...
> If you've got two power supplies in the game, make damned sure you've
> tied the GNDs together.
>
Anonymous
June 1, 2005 4:02:17 AM

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

I ran into a similar problem once and it turned out to be caused by a very
strange circuit on the motherboard.

Look at the 74HC138 chip at location B6. You should be getting around 5
volts at pin 6. If you don't, the board won't work. This voltage comes
from a zener diode, D4 = 1N4733A. Its cathode is supposed to be connected
to +11.5 V DC unregulated.

Lord knows why Gottlieb decided to do this. If you don't have your +12
volts connected to the motherboard, the game won't start up and all you'll
get is garbage.

Ah, I remember now -- someone in the past had upgraded the cabinet from the
original power supply to a switcher, and had neglected to connect that vital
+12 volt line to the new power supply.

Hope this helps!

Matt J. McCullar
Anonymous
June 1, 2005 6:59:55 AM

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

Thanks Matt, and everyone else for the replies. I'll keep you posted on
my progress.

Jeff

Matt J. McCullar wrote:

> I ran into a similar problem once and it turned out to be caused by a very
> strange circuit on the motherboard.
>
> Look at the 74HC138 chip at location B6. You should be getting around 5
> volts at pin 6. If you don't, the board won't work. This voltage comes
> from a zener diode, D4 = 1N4733A. Its cathode is supposed to be connected
> to +11.5 V DC unregulated.
>
> Lord knows why Gottlieb decided to do this. If you don't have your +12
> volts connected to the motherboard, the game won't start up and all you'll
> get is garbage.
>
> Ah, I remember now -- someone in the past had upgraded the cabinet from the
> original power supply to a switcher, and had neglected to connect that vital
> +12 volt line to the new power supply.
>
> Hope this helps!
>
> Matt J. McCullar
>
>
>
!