Homebrew PCBs

Stefan,  This one you will appreciate - please read.

I was looking over the PCB for the printer trying to find the opto 
and the triac.  I am studying it like crazy - components on one 
side, traces on back side trying to figure it out.  It's not a dense 
board by any means, I am just stupid.  Anyway, to figure out what is 
what, I would go to mouser and digikey and type in the part numbers 
of the various components - didn't help at all.

So, while just staring at the PCB I noticed something interesting in 
the legends - the board is divided into two sections -primary and 
secondary.  There are three, 4 pin DIPs bridging that outline and 
one big transformer.  After thinking about that for a moment, I 
realized that those 3 small ICs are going to be the optos which 
isolate the primary from the secondary !

Kinda neat how HP laid out the board like that.  I will try to get a 
photo of it.

chris



--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:
>
> On Fri, 02 Dec 2005 19:40:20 +0100, lcdpublishing  
> <lcdpublishing@y...> wrote:
> 
> >
> >
> > BTW, is this isolator needed for the same reason I needed one on 
my
> >
> > spindle driver that fried my computer last year?
> 
> 
> Yea, more or less. it isolated the thermisotor and pot and supply 
from  
> mains, which isn't all designed to be at that 
potential, 'specially the  
> thermistor. Often it will be a phototriac which does the firing of 
the  
> triac the right way without hassle at a zero crossing.
> 
> ST
>