Osborne 01 computer smoked..

From: Lawrence Walker <lwalker_at_mail.interlog.com>
Date: Fri Sep 4 11:33:11 1998

On 4 Sep 98 at 13:12, Philip.Belben_at_powertech.co.uk wrote:

> Larry and Tony are discussing a blown capacitor...
>
> >> 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.
>
> [...]
>
> > 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 ?
>
> Eh? 6V 6W bulb is exactly what Tony suggested.
>
Oops. I meant 6V 9W

> To be more specific, many power supplies have regulator circuits that
> expect some current to be flowing in the load. These PSUs will push out
> the wrong voltages, or shut down altogether, if you power them up with
> nothing on the output.
>
> Therefore, when testing power supplies, connect some sort of load device
> - it doesn't matter what as long as it draws roughly the right amount of
> current - to the output. Most computer PSUs regulate the voltage on the
> 5V rail and hope all the others will follow, so this is the best place
> to connect the load.
>
> Light bulbs make good dummy loads because (a) they light up when the
> current is flowing and (b) they are relatively small, cheap and easy to
> obtain compared with (say) resistors of similar value.
>
> 12V bulbs (e.g. car running lamp (0.3 A) or indicator lamp (1.75 A)) are
> good for loading 12V lines should you need it.
>
> 6V bulbs are good for loading 5V lines. 6V 6W flashlight bulb is good
> for small and medium PSUs; for larger power supplies I use a 6V 24W car
> headlamp bulb (yes, my truck has 6V electrics). 12V bulbs also work at
> 5V, but remeber they have a much lower resistance at 5V than they do at
> 12.
>
> DON'T use the "power good" line to connect the dummy load. This is a
> digital output - usually TTL level - which can only drive a few mA.
>
 Hmmm. Now I'm confused (as always). Wouldn't that mean you'd have to
leave the "power good" (orange ?) line connected to the motherboard otherwise
the PSU would shut down ? Was why I mentioned the higher W rating.

> DO connect the "voltage sense" line(s) to the load as well as +5V and
> ground.
>
> Philip.

 Ahh this seems like the source of my confusion about this. What is the
difference between the "power good" and the "voltage sense" lines ?
 For example, most of computer PSUs I've seen have up to 12 lines connected
to the MB sometimes segmented into 2 groups. One of these groups has a
uniquely color-coded line ( orange ?) which I took to be the PG line. the
conectors for the peripheral devices have 4 lines 2 of which are usually black
(ground or neutral) and there's usually a red which I believe is "hot or
positive" Is the 4th line (usually blue or yellow) the "voltage sense" line ?

BTW is there any color-code convention for wire like the one for resistors and
other components ? Green is always ground in most applications for example.

 I also have an IBM 8557 which is a SCSI mchn that has 4 heavy-guage red and
black connected to the PSU as well as a connector with 7 smaller guage wires
( 2 blu, y, wh, or, bla, brn). The heavy guage are obviously power but what are
the rest for ? The orange I take it is PG ,the black neg. or return. The device
plugs are red, bla, bla, blu. no smaller perp. plug. I guess the 3 1/2" FDD
takes power from the SCSI bus.

ciao larry
 
lwalker_at_interlog.com
Received on Fri Sep 04 1998 - 11:33:11 BST