[Coco] More MPI mischief...

[Brian Blake]

Well, problem solved.

I tested the O-90 for sound in four different MPI's (including a 3024 PAL
upgraded one that has known issues with this O-90 and FDC's). Three out of
the four had sound. So I think it was safe to say the O-90 was not the
culprit.

So, I started doing some continuity tests, from pin 35 of the cart
connectors back to pin 35 of the male card edge connector. That was an open
circuit. So I started from pin 35 and worked my way back and found the
problem. Under C10 of the MPI, there are 2 via's; one connects to pin 35 of
the male card edge connector, the other goes back (thru several other via's)
to pin 35 of the 4 cart connectors. On this particular MPI, there was
nothing connecting the 2 via's underneath C10. Soldered a jumper wire from
the via closest to the male card edge pin 35 to the via closest to the cart
connector pin 35 and I now have sound out of my MPI with the O-90 in it.
Wish they were all that easy...

As always, thanks for the help and suggestions again guys.

Brian





On Wed, May 5, 2010 at 11:56 PM, Robert Gault <robert.gault at att.net> wrote:

> Brian Blake wrote:
>
>  From my under-educated point of view, it appears to me that I am looking
>>> at
>>>
>> only a few possibilities possibilities: Broken trace on the MPI (would
>> that
>> prevent the music from actually starting)? Weak power supply in the MPI
>> (doesn't makes sense if the FD-501 works fine)? Piece of debris shorting
>> pins 33/34 to pin 35? (I would assume grounding out pin 35 would kill all
>> sound from the CoCo, this does not happen as I can play games loaded via
>> the
>> MPI and still have sound).
>>
>> Any other thoughts or suggestions?
>>
>>
> Make sure that the Orc-90 is actually sending out sound by putting an AC
> voltmeter on the output RCA jacks or connecting them to a sound system. If
> these have sound, then there may be a problem with the Orc-90 opamp IC6 or
> the Coco DAC is not getting sound from the CART input.
> You may be able to test the Orc-90 IC with the pak open so a meter reading
> at IC6 pin1 can be made.
> If you have some other sound source that you can safely connect to the CART
> port pin 35 even through the Orc-90, you can test the Coco side. Just
> remember to turn on the Coco sound and point the MUX at the CART.
>
>
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