[Coco] sc77527p, AKA SALT chip

[Gene Heskett]

On Sunday 12 January 2014 23:19:48 Gene Heskett did opine:

> On Sunday 12 January 2014 21:32:54 Luis Antoniosi (CoCoDemus) did opine:
> > Page 39 of coco2 service manual. There is one i uploaded to
> > colorcomputerarchive.com
> 
> That is the same thing I have, and like my copy, does not show how the
> +5 volts it regulates is connected inside the chip.  And that is the
> info I need to make a semi-intelligent attempt to change how I power
> its innards.
> 
> What I am tempted to do is, since it all runs on the + & - 5 volt
> internal, is to disconnect the 5 volt feed with a 10 ohm resistor in
> series with it from pin 3 and reconnect my present +5 to the emitter of
> where the pass transistor was, and disconnect the +12 volts from pin
> 16.  That should get the 5 volts into the chip on 1, 2, or 3.  Leave
> the -12 connected to pin 15, or run it thru an LM7908 to reduce it to
> real coco voltage.  And I'm still stirring around in my midden heap
> looking for a small heat sink.  I am convinced I have 2, suitable for a
> 14-16 pin dip, in a yellow shack pegboard blister pack, someplace.  But
> the heap has gotten pretty deep in 20+ years. And little  always
> filters to the bottom of a 2 foot deep box. Murphy's Law corollary &
> all that rot. :(
> 
> Thanks for the url though.

Well, that is not a workable solution, the chip gets quite warm in about 
1.5 to 2 minutes. And the coco3 is crashing instantly without ever showing 
a boot screen.  So tomorrow I restore the 1/16" long cut isolating pin 16 
and see if that will then bias this internal regulator that normally drives 
the big TO-220 pass transistor & see if that cools it off.

Am I the only one that has ever done this to his long suffering coco3?

Cheers, Gene
-- 
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