[Coco] More MPI mischief...

[Joe]

I had a similar problem with the A15 line. Seems like the Quality control 
was not to great near the end.
----- Original Message ----- 
From: "Brian Blake" <random.rodder at gmail.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Thursday, May 06, 2010 8:57 PM
Subject: Re: [Coco] More MPI mischief...


> 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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>
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