Re: Missing caps on Gravitar, Black Widow,

Kevin Moore <talon.k@gmail.com> writes:
>
> So I've been working on some Black Widow boards, and Gravitar boards, and
> I've noticed that the caps C34,and C28 are missing. Both these caps are on
> the audio amp circuits for the LM324 chips.

Interesting.

As a point of reference, I have a Gravitar board in which both C28 and C34
(and all discrete components around B5 and D5) are present.

It's labeled A03898-12 (with the part number in solder mask, the "12" in ink).
It currently runs Gravitar and Black Widow via a bank-switching hack. I've
forgotten whether I first got it as a Gravitar or Black Widow.

> One Gravitar board someone had placed a cap on it, and I was missing half
> the sounds from that board until I removed the cap. So I'm wondering if this
> was a design flaw and there was a field service document stating to cut them
> off.

The caps appear to be small decoupling-style caps.

According to TM-232 (Gravitar to Black Widow Retrofit):

  http://arcarc.xmission.com/PDF_Arcade_Atari_Kee/Gravitar/Gravitar_Black_Widow_Retrofit_TM-232_1st_Printing.pdf

To convert a Gravitar to Black Widow, C28 and C34 (0.22uf) "are to be
removed", because "these components are not used in the Black Widow game."
C27 (0.001uF) is to be replaced with a 100pF capacitor, and R46 (10 kOhm)
is to be replaced with a 22 kOhm resistor.

At a glance, I think the only differences are going to be in the volumes
of the various sounds as mixed through the 7 op-amps (3 at D5, 4 at B5)
in question, but that just might explain why "half" the sounds are missing.

(My memories of Black Widow in the arcade are sufficiently foggy that I
can't tell if my ROM-swapped board with Gravitar components still intact
is inaccurate. Or, if the arcade in which I played Black Widow didn't have
a tech who took the same shortcut :)

Later,
Doug.
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Received on Mon Jan 24 02:17:33 2011