[Coco] Re: fuzzy deuce?

Richard E. Crislip rcrislip at neo.rr.com
Fri Apr 16 14:38:30 EDT 2004

Hello RJRTTY at aol.com

>     During work on my repack I found out why the RF out on the coco3 is
> generally cleaner than a coco1 or 2. At first I powered the main board by
> putting 24 V DC across the main diode bridge at the point where the AC
> transformer was connected. Everything seemed to work fine until I noticed
> I had no sound and no RF output. It turns out that a a seperate power
> connection on the ac side of the bridge was connected via an electrolytic
> capacitor to a seperate pair of diodes which then connected to an
> independent voltage regulater outputing 8 Volts. The sound interface and
> RF modulator both use this independent voltage source to avoid the noise
> on the main supply. Just when you think tandy suffered from a lack of
> comittment when it came to certain aspects in the design of the coco3, you
> find something like this. It works so well that I am going to duplicate
> the circuit on a seperate board outputing buffered sound and video for
> some of my coco 1 and 2's.

I and a friend were also wondering abou that 8 volt circut. Thanks for the
explaination. I, like you have decided to use that native power supply, but
I'm going one step further, I think I'll stick with the MPI's native power
supply too. I will stick some fans in there to keep things cool and use the
PC case power supply to power the FDD and HDD. I decided to do this because
all the instruction for repacking the MPI seem to be amied at the newer
models. I have a older one and what I see after opening the case does not
come close to what is described in the documentation I have and since it''s
the *only* MPI I have..... well you get the picture. Frankly the slot
grounds are soo rusted, I can't believe it's still working at all. On two
the slots, the ground strips on one side have fallen off due to the rust.
Is this normal? I mean I was flabbergasted when I opened that case.

Cruisen                                                    _|_
              on AutoPilot with an Amiga   ---o-( )-o---   and a CoCo

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