Vectorlist Archives: DAC -> Op-Amp testing (was RE: TECH: Tem

From: David Shoemaker <davids_at_oz.net>
Date: Mon Nov 23 2009 - 01:51:29 EST

Going to resurrect a VERY old thread here.

The part I have a question about is:

"There are more elegant procedures for troubleshooting this if you have the
right test equipment, but without it, it would be faster to just replace
these components in the order given. "

So I have a tempest board with no X deflection. As far as I can tell there
is either a dead AM6012 @ A10 or a dead TL082 @A11. I come up with this
because there is no output at pin 7 of the Tl082.

But I can't be sure because when I scope pin A11:6 (from A10:18 I get a flat
line). But I also get a flat line on the equivalent signal on the Y side
which is working fine.

So anybody know just what the "more elegant procedures" are that Joel was
speaking of here? I assume the DAC is current mode into the first stage of
the op amp as such there is nothing for the scope to sense and display.

Thanks,
David

-----Original Message-----
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Joel Rosenzweig
Sent: Wednesday, August 04, 2004 5:20 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: TECH: Tempest PCB

Steve,

The single line that you see is due to lack of deflection in the opposing
axis. If the display shows a horizontal line only, then your vertical
deflection circuit on the Tempest board is faulty. Because Tempest is a
portrait mode oriented game, the axis are reversed, so you'd be looking at a
"X" deflection circuit failure. If the display shows a vertical line only,
then your horizontal deflection circuit on the Tempest board is faulty. And
in this case, you'd be looking at the "Y" deflection circuit. On a
landscape mode game, the "X" is horizontal and the "Y" is vertical. From
the monitor's perspective, "X" is always horizontal and "Y" is always
vertical, but this nomenclature is a little awkward when we rotate the
monitor!

The Tempest board has X,Y, and Z outputs. The "X" output is actually
connected to the "Y" input on the monitor, and the "Y" output is actually
connected to the "X" input on the monitor.

The analog output section for each axis is made of a digital to analog
converter and some op-amps. The likely scenario is that you have an op-amp
failure after the converter. Give thought to replacing the TL082 (op-amp)
first. If that doesn't work, replace the MC1495. And if that doesn't work,
replace the AM6012 DAC.

There are more elegant procedures for troubleshooting this if you have the
right test equipment, but without it, it would be faster to just replace
these components in the order given.

Regards,
Joel-

----- Original Message -----
From: "Steve P." <projektzwo@yahoo.com>
To: <vectorlist@vectorlist.org>
Sent: Wednesday, August 04, 2004 11:26 AM
Subject: VECTOR: TECH: Tempest PCB

>
> Hi everyone.
>
> I have 2 Tempest PCBs that I could use some assistance with. I am NOT an
> electronics guy, so my tech skills aren't great.
>
> The first one is working and playable. It has an odd habit though of
> resetting for no appearent reason. This usually happens in the red or
> yellow tubes. Game will be playing right along and ZAP! resets and goes
> into attract mode. I've swapped AUX boards, reflowed solder on the
> interconnect cable connections, swapped ROMS sd well as the other socketed
> chips and still get the odd reset... Any ideas?
>
> Board number 2 has a graphics issue. PCB coins up and plays but the
display
> is squished into a bent line. Checked the vector trimmer pots and they
seem
> ok. Also did the same swapping of parts on this PCB that I did on the
> first. LMK if anyone would like a pic of the screen.
>
> Thanks in advance!
>
>
>
> -Steve P.
>
>
> --------------------------------------------------------------------------
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DAC -> Op-Amp testing (was RE: TECH: Tempest PCB)