Broken Mac Accelerator

[Jeff Walther]

>Date: Fri, 8 Sep 2006 22:41:09 -0400
>From: "Teo Zenios" <teoz at neo.rr.com>

>My latest acquisition came in today, a Mac IIci, that I wanted to 
>use as an OS 6.08 machine
>  with a Daystar Turbo 040 (68040/33) accelerator. Anyway after 
>cleaning up the system and

>  I took the card out and notice there was a capacitor missing on the 
>back with a nasty looking
>  black burn mark. So I started looking around inside for the burn 
>metal part and notice I did not
>  smell or see smoke or little capacitor parts (its a surface mount 
>with no numbers on it)

>So what I want to know is how the thing functioned at all without 
>the cap (burnt carbon acted
>  as a capacitor in some way)? and what caused it to stop working.

It looks as if that cap (C54) ties the upper righthand pin of the 
oscillator, which I think is pin 14 or Vdd.

As someone else wrote, it is probably just a decoupling cap, but it 
may be hard to tell for certain as I believe that the Daystar boards 
have more than four layers, which means that there are traces we 
cannot view.

>If anybody have an original Daystar Turbo 040 33Mhz card with the 
>cache on a separate board
>  could you let me know (if possible) what value C54 s supposed to 
>be? The cap looks to be tied
>  into one or two legs of the oscillator chip that controls the CPU 
>(Ecliptek EC1100 16.667Mhz
>  93-10).

There are no markings on C54.  It looks just like the two caps next 
to (below) it, but there are no characters which would betray a 
value.  I don't have a capacitance meter.

Jeff Walther