Sun 3/80 Magic Smoke

Tried to power up a Sun 3/80 mainboard...

Inductor L0500 (right near the power input) (I assume this
is an 
inductor by the L0500
marking on the PCB) smoked....  (pink smoke no less)

Anyone familiar with the 3/80 to give an idea of why this
might have smoked.

Board appears in excellent condition, no foreign objects on
the board, 
no sign of any
shorts that I can see.

Would like to rescue this board.  If it was a PC I'd look
for bulging 
electrolytics...

Anyone got a schematic for the 3/80 ?  (I've never seen any
Sun schematics).

-- Curt

On Saturday 10 May 2008 20:56, Curtis H. Wilbar Jr. wrote:
> Tried to power up a Sun 3/80 mainboard...
>
> Inductor L0500 (right near the power input) (I assume
this is an
> inductor by the L0500 marking on the PCB) smoked.... 
(pink smoke no less)
>
> Anyone familiar with the 3/80 to give an idea of why
this might have
> smoked.
>
> Board appears in excellent condition, no foreign
objects on the board,
> no sign of any shorts that I can see.

If that's indeed an inductor maybe there is a short that
isn't obvious?

> Would like to rescue this board.  If it was a PC I'd
look for bulging
> electrolytics...

Any tantalum caps on that board?


-- 
Member of the toughest, meanest, deadliest, most unrelenting
-- and
ablest -- form of life in this section of space,  a critter
that can
be killed but can't be tamed.  --Robert A. Heinlein,
"The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled
by lies. --James 
M Dakin

> 
> 
> 
> Tried to power up a Sun 3/80 mainboard...
> 
> Inductor L0500 (right near the power input) (I assume
this is an 
> inductor by the L0500
> marking on the PCB) smoked....  (pink smoke no less)

This sseems to be the day for smoking indcutors 

> 
> Anyone familiar with the 3/80 to give an idea of why
this might have smoked.

I've never seen this machine, but from the location of the
component, and 
the fact that it's an inductor, I would asseum it was part
of a DC power 
line filter, and it smoked because of a short (to logic
ground, most 
likely) 'downstream' of said component.

My first suggestion is to desolder the indcutor from the
PCB. Then trace 
one of the connections back to the PSU input connector,
which will tell 
you which power line it's associtated with. If you're lucky
it'll be 
something like a +12V rail, not used by many components. If
you're 
unlucky, it'll be the 5V rail that goes everywhere...

Msot likely you'll find the 'other' side of the inductor
postion on the 
PCB -- the one not conencted to the power connector -- has a
low 
resistnce to ground.

There are many 'techniques' for finding such shorts. Pulling
all socketed 
devices is a good first step, if the short goes away, you
know it's one 
of the chips you've pulled. Suspecting tantalum capacitors
is another 
good idea . More
logical is the idea of applying a low voltage between 
the output side of hte inductor and ground, so that a
mdoerate current 
flows (I would guess areound 1A would be OK here), and using
a sensitive 
millivoltmeter to measure the voltage drop across
components. The shorted 
one will test lower than all the others (due to the drop
along the PCB 
tracks), but you do need a good millivoltmeter for this
test.

-tony