Will an xt compatible run a 486 board. Ie: are the voltages the same even
though the wires are differeent colors.

29 responses total.

Yes.  It should work.  I'm doing exactly that with the 486 board I got
from you.  It's in an XT case with 130W supply, 200M HD, 5 1/4" floppy,
3.5" floppy, CD ROM, 16 bit Sound Blaster, etc.  No problems.

Very cool.I'm glad that is working out for you.

My Leading Edge XT uses a different connector for power.  :(  Only one board
going in that case I guess.  

Wack the connector off the end of a dead power supply and splice it onto
the wacked end of your LE XT supply ;-)

Well, the XT also has a dead serial port on it that I can't seem to dissable.
Anyone have the setup utility for the Leading Edge XT with extended video
bios?  I have most of a simple 486 system to play with now, so the LE doesn't
draw much of my attention.

I may have the rest of the 486 system that I would be interested in getting
rid of, what are you missing?

Right now I'm missing a floppy, and any kind of fixed disk.  Depending on what
happens I may have a 200 conner to migrate into it.

As I remember, Leading Edge XTs didn't have a 'setup utility', just DIP
switches.  If you want the switch settings, tell me and I'll see if I
forgot to sell the manual along with that machine I used to have.

There was a setup utility that I got into, but I have since lost it.
I could do strange things like mess with the interlacing of the display.
There were other usual settings, too.  I have a feeling that the util
needs to be run under certain versions of DOS, and I've been messing
with it in that respect.

Any idea what BIOS it has?  On some machines with Phoenix BIOS's, you hit
Ctrl-Alt-C to get into the setup utility.  I worked on a Leading Edge
386SX/15 that was that way.

Phoenix 8088 ROM BIOS Ver 2.13
Copyright 1984, 1985
[ctrl]-[alt]-c doesn't seem to work.  I'm pretty sure I ran a program to get
in, but the only thing that looks anything like it might be it complains of
wrong version of dos or something similar.  Now I can't even find the program.

Try ctl-alt-esc, ctl-alt-backspace, etc., too.  But you probably need a
program.

try starting up with the keyboard/mouse unplugged. Or  change something else
that the system will detect as an inconsistency with bios settings. Remove
the battery but you would want to be sure you know how to reinstall the hard
drive, etc.

If he can't get to setup mode I don't think he wants to try killing his cmos
settings by removing the battery.

I'm under the impression that, unless this is like a ps2 which does require
a special disk, the cmos will ask to be reset. Not true here?

and another soetimes-it-works trick is to reboot with ctrl-alt-INSERT
and see what happens. this is after the machine is already on.

(This is as good an item as any for this...)

I need a power supply that provides 3 volts at ca. 1 A. I read that a
317T regulator will allow adjustment of its output from 1.2 to 27 volts
with a 40 volt source, but the book doesn't say at how low an input
voltage the regulator will work to yield 3 volts (regulated). I would
*think* it would only need the usual couple of volts required by 
similar regulators, but I don't know that for sure. What's the case?

The spec. is 40 v maximum output to input differential.  The operating
curves indicate a 2 v operating differential with 1 A of current draw
at 25 C to 150 C.  (Don't run it that hot!)  2.5 volts of headroom
should be all you need unless you want to hug the 2 volt line to minimize
inefficacy.

THanks, Klaus. The application is to run a tiny 3-V motor. I would think a
filtering capacitor is needed on the input, but wonder if one is needed on
the output. The book also mentions bypassing the adjustment terminal to
reduce ripple. Do you know how that is done?

It depends on your power source.  Batteries are basically large capacitors.
I'd put a 10 uf electrolytic right on the output terminals and a .1 uf
across the input.  Don't worry about bypassing the adjustment terminal.
I doubt you would notice the difference running a motor.  Beside, if you
do that you also have to add a diode to protect the regulator should Vout
drop below ADJ.  Another good way to blow a regulator is to have Vout
greater than Vin.  If your application might motor the motor causing it to
become a generator, it would be a good idea to put a normally back biased
diode from Vin to Vout.

I was going to install the diode. My power source will be a 6.3V x-former
into a bridge rectifier (because I have the parts) so I plan on putting
a big cap on the input. The motor will have inertia, so will produce a
back emf to the regulator if the AC power is cut. 

(While I have your attention - do you have any suggestion on line filters
for motors, which I asked about in another item, to keep the startup
hash off the line? Type? Size?)

Put a .1 uf ceramic across the wires to the motor and a .1 from each wire
to the motor case.  Do this as close as possible to the motor.  You can
put a back EMF diode across the motor at this point while you are at it.
If you ever look inside a cassette player, you will see that this what they
do, often inside the motor. (Many of the motors also have built in mechanical
or electronic speed regulators.)

Uh...I think I've introduced confusion between a) and b). a) is the
tiny 3V "toy" motor, which is not a noise problem. b) is a furnace blower
motor that is somehow introducing "hash" into the telephone lines on
startup. The questions re a) have been resolved. Putting 0.1s on b)
can short out carrier-current controls, so I'd prefer a line filter
(which has inductance on the line side). b) is what my second question
in #21 was about. 

I have nothing of note to say about problem b).  Perhaps the phone
wires and furnace power wires are running close together. Could be
that the phone wires aren't a twisted pair and therefore the noise
is not common mode.  Might be some device plugged into the phone
line and the power line that is coupling one to the other.  Possibly
even the modem.  The noise may even not be getting in through the
phone line but through the power line.

OK, those are my conclusions too (short of inspecting the system). Are
you familiar, however, with the line filters that one can wire in? They
are L-C devices.

A filter to filter what?  The power to the modem, the power to the
furnace or the phone line?  Does he have a furnace with electronic 
spark ignition?

It's an electric furnace - i.e., a central furnace with an electric
heating' element and hot air distribution. The "b)" filter is to filter
out the blower motor startup "hash". The line filter that could be used
for this is a metal can with two line side terminals, two device (motor) 
side terminals, and a ground terminal. The circuit is two inductors, one
on each line side, and then a pair of capacitors in series across the load
side, with the center point grounded. They are commerical units costing
$10-20. They are usually just rated in amps, though I'm not sure how to
choose that for a motor, because of the startup surge. 

He may need more than just a filter.  It could be that the motor starting up
is drawing enough current to drop the line voltage which in turn causes
problems with the modem or computer.  (BTW, my Mac SE proved to be *very*
resistant to voltage sags.  One time the power dropped to 68 volts at work.
My HP 486 took the dive.  Just for yucks, I turned on my SE and it came up!
I had the only working desktop computer in the whole plant that wasn't running
of a UPS.)

Oh, sorry.  Got distracted.  If you try the filter, be sure to get one
rated the same current, or greater, as the fuse or circuit breaker in the
fuse panel.  It's the CB's job to blow under a fault condition, not the
filters.

Good points! I will follow up on both.

Response not possible - You must register and login before posting.

- Backtalk version 1.3.30 - Copyright 1996-2006, Jan Wolter and Steve Weiss