Osborne 01 computer smoked..

From: Lawrence Walker <lwalker_at_mail.interlog.com>
Date: Thu Sep 3 18:43:09 1998

On 3 Sep 98 at 18:35, Tony Duell wrote:

> >
> > The board mesures 4 by 7inches and looks very clean, exception of the Cap that
> > blew, The fuse is not blown either.. LIke I said I shut it down as soon as I
> > saw smoke..
> >
> > The Obvoius bad component is the Capacitor (Its cracked on has skicky stuff
> > leaking out)
> > The Value is 0,1uF_at_X , brand is Rita, GPC , 250V-MP
> >
> > On inspection this looks to be the only bad part.. It is next to, in fact
> > touching against I think a diod or transistor , its black with 3 legs (Wires)
> > on it (GI KBP-10 8210)..
> >
>
> Hmm... The 'X' on the capacitor makes me think it may be part of the
> mains filter network. And these caps fail for no good reason and do no
> other damage.
>
 Tony, I tend to be a board switcher now (shame) and I usually just replace the
defective component. When I first started I was more investigative and would
replace defective diodes etc. Dried out caps is common in older equipment and
while i've occasionally replaced them as in old audio equipment, I've always
tended to think that they would take out other parts of the circuits with them.
 Does the cap short or open when they dry out ? Thinking about it , it makes
sense that they would not damage other components as long as they did not short
or be able to charge.
 Is this why you get failed PSU.s commonly with an intact fuse ?
 I've had 3 or 4 IBM PSU failures recently and have avoided trying to repair
them since I think that a failed power transister usually took a bunch of other
stuff with it and I think my time is more valuable than trying to track it
down. Are failed electrolytyics the most common source of failures. ?
 Another source is a fan disfunction with heat causing failure. What circuit
component is most likely to die under those conditions ? Having an overview
of this you could quickly check the most likely offender and desolder it to
check it . Of course if you had the circuit diagrams you could figure out the
RC, pi, etc. functions but I retain little of the theory I studied long ago.
 Whatever the lackings of the IBM service manuals, they , like the army
give you step by step processes and leave little to initiative.

> > I am not a professional board level techniction, but I do have alot of
>
> Nor am I!
>
> > experiance soldering and working with electronic components.. I have basic
> > tools like: Soldering iron, Ohm meter..
> > I should be able to reoair this myself with (Like the song goes) "A Little help
> > from my friends"
> >
> >
> > So What do you think?
> > Should I just replace the Bad Cap and plug it in again?
>
> I'd replace it. A 250V _AC_ capacitor, class X. You should be able to get
> that from a good parts company (alas, being in another country I can't
> help you there).
>
> Then try again. Put the PSU on dummy load if you like (I certainly would)
> - a 6V 6W bulb on between the +5V output and the 0V pin. Let it run for a
> few minutes - taking care not to touch the PSU board as there's mains and
> rectified mains all over it. If it runs for (say) 5 minutes on dummy load
> it's safe to try it in the computer again.
>
> > Do you think it blew because of another shorted part ?
>
> No, I think it just failed.
>
> -tony
>
 You have referred before to this dummy load 6V 6W device. If my
memory of Ohms law hasn't failed me completely this works out to
a 1 amp limit. I also imagine this has to be on the power good line.
Is there any reason you use this configuration ? I have some old 6V 6W
bulbs . Would these work just as well ?

 I must admit that you and Jason P have inspired me to go back to basics.
 I should warn you I have an IBM PS1 SVGA monitor I just acquired that
I will be asking for guidance on , and if the stuff thats been on the list
lately isn't off topic a svga sure as fuck isn't. :^))

ciao Larry
lwalker_at_interlog.com
Received on Thu Sep 03 1998 - 18:43:09 BST