10 May
2008
10 May
'08
8:56 p.m.
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
10 May
10 May
9:57 p.m.
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
11 May
11 May
2:37 p.m.
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
14 May
14 May
3:33 p.m.
Tony Duell wrote:
I'm unlucky... it is 5V.
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.
I've pulled all socketed components (NVRAM, CPU, FPU, SIMMS, LSI ? chip,
BOOT ROM)... still smokes.
I've identified 13 surface mount capacitors (not counting teeny ones) on
the top
side of the board that tie between 5V and ground. On a good board, I
get two
slightly different ohms readings (39.1 and 39.4 depending on which cap)
between
their + side and ground. (I'm guessing two different 5V 'rails')
On the bad board, I get the same reading on all of the 5V caps.
What are the chances that one of these caps are bad ? I know tantalums
tend to
short, but since I'm familiar with tantalums from working on 80s arcade
games,
I'm used to the 'bulb' with two legs variety of tantalums. I wouldn't
know how
to tell if these surface mount caps are tantalum or not.
Short of pulling these caps one at a time and metering them out of
circuit (I have
soldering equipment, but it isn't intended for surface mount... not that
I haven't
pressed it into that duty before... but because it isnt the 'right'
tool... it is tedious
and frustrating to make it work for the task... although it isn't too
bad on components
with just two connections).
So far despite the 'smoke' tests.... the inductor has not burned open
yet. I doubt it's
value is particularly correct at this point... but I can worry about
that if I can find
and clear the short. It is like a 1watt ? resistor with bands:
silver, black, brown, tan/gold ?, and then a very wide silver band
(which must be a
multiplier, tolerance, etc)
Any further suggestions, or should I start pulling caps ?
-- Curt
-tony
5:21 p.m.
Eric Smith wrote:
Curtis wrote:
drat.... how can I find out what is shorted... the whole board uses
5V... that means it
could be any component.... but no components are puckering, blistering,
smoking (other
than the inductor), etc....
Maybe I'm not going to get this board back ?
-- Curt
I know tantalums tend to
short,
They may short, but usually only in the process of going open in a
spectacular way. If they don't look abnormal, and the ohmmeter doesn't
indicate that they're shorted, then they aren't your problem.
Eric
5908
days inactive
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ard＠p850ug1.demon.co.uk -
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