Computer won't post with my favorite keyboard plugged in.

I forgot to mention: another thing that might help is changing the value
of any power-on reset capacitor, especially if your keyboard works
when you hit the hardware reset button on your computer.
 
"Michael Black" <et472@ncf.ca> schreef in bericht
news:alpine.LNX.2.02.1307101638590.7921@darkstar.example.org...
On Wed, 10 Jul 2013, petrus bitbyter wrote:


That "Opps" is the reason that breaking a pin would be my very last
option.
It should not be that difficult to interrupt the reset line on a place
and
in a way it can be restored if necessary. Very unlikely? You just proved
the
opposite :)

That's simple then. Grab a female connector that matches the keyboard,
grab a male connector that matches the computer, and wire them up, leaving
off the reset line.

Or most keyboards, the cable plugs into a connector inside. So it's easy
to cut the wire there. Indeed, at one point I needed a small connector
keyboard and didn't have a suitable one, so I was going to take a cable I
did have that had the small connector and use it rather than the
keyboard's original cable.

If the keyboard really is drawing too much current, then clearly something
in the computer is between the +5v line and where the keyboard plugs in.
So bypassing that whatever would fix it, if this is the problem.

Michael
Click to expand...
If you modify that brandnew machine you will loose all guarantee.

First thing to do is making a breakout cable and measuring the power and
reset lines using a voltage meter. Especially looking for differences
between the old and the new keyboard. Clock and data lines are important as
well but a voltage meter may not do. An o'scope will... If only you have
one.

There's one much more complex possibility for the cause of the problem:
Noise from the keyboard. Some of that older keyboards are a little bit noisy
and maybe the new machines inputs are to sensible. Fighting this problem
requires some filtering which in turn requires experience and experiments.
There's no general prescription for it.

One thing can be tried easily however: Some ferrite clamp(s) on the keyboard
cable. If the keyboard is radiating noise *and* if that noise is picked up
by the cable *and* if the computers input(s) cannot handle it *then* you
have a good chance to fix the problem with it. Conducted noise cannot be
fought this way.

petrus bitbyter
 
On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.
Click to expand...
Not in the USA. A computer is considered "open architecture" and can be
modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.
 
"dave" wrote in message
news:kYadnR91LsqHLkPMnZ2dnUVZ_sudnZ2d@earthlink.com...

...in the USA. A computer is considered "open architecture" and can be
modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.
Click to expand...
Adding or changing cards or peripherals? Yes. Altering the wiring? I doubt it.
 
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can be
modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
Click to expand...
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty. Of
course, that only matters if you need the warranty, ie the computer fails
and you want to send it back.

Michael
 
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty. Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Click to expand...
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?
 
On 07/11/2013 12:25 PM, mike wrote:
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty. Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?
Click to expand...
Did you check if the RESET pin is tied low on your keyboard? Pin 3 of
the DIN plug...isolate that pin with a DIN jumper (5 pin female to 5 pin
male) that only uses four wires.

John :-#)#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
"mike" <ham789@netzero.net> schreef in bericht
news:krn0hb$53t$1@dont-email.me...
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty. Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?
Click to expand...
Er... No. So your old keyboard requires 180mA. Did it work correctly on the
old machine that way? If so, can your new machine provide that 180mA? *If*
not, *then* your solution makes sense *otherwise* its only a maybe.

From your information it is not clear on what conditions the keyboard worked
all these years. If 5V/180mA does the trick and your new machine can provide
it, lack of power is not the main problem. The 5V/180mA is not all that bad.
In the old days the keyboards often were protected by a 1A fuse.

To check it out, you first connect the old keyboard to an old machine. You
will find the required current. Suppose that's the 180mA. Now connect your
new keyboard to the new machine. The 5V/10mA should do. Disconnect the new
one and connect the old one. Now if the machine cannot provide the power
required you should find the 5V dropping. If not, the machine does not seem
to have a problem providing the required current.

But if you new machine cannot provide enough power, your method is not 100%
save. Problems may arise when you shut down the computer while the wallwart
is still going on. I ever found printer ports blown when the computer was
powered down before the printer. So to stay on the safe side I'd use the
10mA from the machine to active a small relay that switches the wallwart
power to the keyboard. Suppose there's plenty of space in the old keyboard.

petrus bitbyter
 
On 7/11/2013 3:52 PM, petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:krn0hb$53t$1@dont-email.me...
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty. Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?

Er... No. So your old keyboard requires 180mA. Did it work correctly on the
old machine that way? If so, can your new machine provide that 180mA? *If*
not, *then* your solution makes sense *otherwise* its only a maybe.

From your information it is not clear on what conditions the keyboard worked
all these years. If 5V/180mA does the trick and your new machine can provide
it, lack of power is not the main problem. The 5V/180mA is not all that bad.
In the old days the keyboards often were protected by a 1A fuse.

To check it out, you first connect the old keyboard to an old machine. You
will find the required current. Suppose that's the 180mA. Now connect your
new keyboard to the new machine. The 5V/10mA should do. Disconnect the new
one and connect the old one. Now if the machine cannot provide the power
required you should find the 5V dropping. If not, the machine does not seem
to have a problem providing the required current.

But if you new machine cannot provide enough power, your method is not 100%
save. Problems may arise when you shut down the computer while the wallwart
is still going on. I ever found printer ports blown when the computer was
powered down before the printer. So to stay on the safe side I'd use the
10mA from the machine to active a small relay that switches the wallwart
power to the keyboard. Suppose there's plenty of space in the old keyboard.

petrus bitbyter


INteresting...
Click to expand...
I follow and agree with your troubleshooting procedure.
But, I have a guiding principle...never ask a question if the answer
won't change the future.
I already know the old keyboard won't work on the new computer.
Plugging it in again just overloads the 5V again. Possible harm, no help.

I believe I have only one option...power the keyboard externally.
That either fixes it or doesn't. That experiment is far easier than
disassembling the machine and trying to reverse-engineer the keyboard
interface.
The risk/reward ratio for messing with the motherboard is unfavorable.

I share your concern about backfeed and originally considered the relay.
But, the only things attached to the computer are two 7406
open-collector outputs and 2.2K pullups.
The third is the reset into a 7406 input. I can probably disconnect that.

If I leave the pullups connected to the computer power, there's no
path from the wall wart power back into the computer????
Solves the problem? yes? no?

As soon as the portable scope charges up, I should have an answer to whether
it works.
 
petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:krn0hb$53t$1@dont-email.me...
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty. Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?

Er... No. So your old keyboard requires 180mA. Did it work correctly on the
old machine that way? If so, can your new machine provide that 180mA? *If*
not, *then* your solution makes sense *otherwise* its only a maybe.

From your information it is not clear on what conditions the keyboard worked
all these years. If 5V/180mA does the trick and your new machine can provide
it, lack of power is not the main problem. The 5V/180mA is not all that bad.
In the old days the keyboards often were protected by a 1A fuse.

To check it out, you first connect the old keyboard to an old machine. You
will find the required current. Suppose that's the 180mA. Now connect your
new keyboard to the new machine. The 5V/10mA should do. Disconnect the new
one and connect the old one. Now if the machine cannot provide the power
required you should find the 5V dropping. If not, the machine does not seem
to have a problem providing the required current.

But if you new machine cannot provide enough power, your method is not 100%
save. Problems may arise when you shut down the computer while the wallwart
is still going on. I ever found printer ports blown when the computer was
powered down before the printer. So to stay on the safe side I'd use the
10mA from the machine to active a small relay that switches the wallwart
power to the keyboard. Suppose there's plenty of space in the old keyboard.
Click to expand...

Take the +5 V from a spare USB port. They provide 500 mA or more. You
may need a resistor to turn the port on. Or find a USB cable used to
power external speakers. The USB to keyboard adapter may provide enough
current, with no modifications.
 
"mike" <ham789@netzero.net> schreef in bericht
news:kro1ej$ucs$1@dont-email.me...
On 7/11/2013 3:52 PM, petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:krn0hb$53t$1@dont-email.me...
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty.
Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?

Er... No. So your old keyboard requires 180mA. Did it work correctly on
the
old machine that way? If so, can your new machine provide that 180mA?
*If*
not, *then* your solution makes sense *otherwise* its only a maybe.

From your information it is not clear on what conditions the keyboard
worked
all these years. If 5V/180mA does the trick and your new machine can
provide
it, lack of power is not the main problem. The 5V/180mA is not all that
bad.
In the old days the keyboards often were protected by a 1A fuse.

To check it out, you first connect the old keyboard to an old machine.
You
will find the required current. Suppose that's the 180mA. Now connect
your
new keyboard to the new machine. The 5V/10mA should do. Disconnect the
new
one and connect the old one. Now if the machine cannot provide the power
required you should find the 5V dropping. If not, the machine does not
seem
to have a problem providing the required current.

But if you new machine cannot provide enough power, your method is not
100%
save. Problems may arise when you shut down the computer while the
wallwart
is still going on. I ever found printer ports blown when the computer was
powered down before the printer. So to stay on the safe side I'd use the
10mA from the machine to active a small relay that switches the wallwart
power to the keyboard. Suppose there's plenty of space in the old
keyboard.

petrus bitbyter


INteresting...
I follow and agree with your troubleshooting procedure.
But, I have a guiding principle...never ask a question if the answer
won't change the future.
I already know the old keyboard won't work on the new computer.
Plugging it in again just overloads the 5V again. Possible harm, no help.

I believe I have only one option...power the keyboard externally.
That either fixes it or doesn't. That experiment is far easier than
disassembling the machine and trying to reverse-engineer the keyboard
interface.
The risk/reward ratio for messing with the motherboard is unfavorable.

I share your concern about backfeed and originally considered the relay.
But, the only things attached to the computer are two 7406 open-collector
outputs and 2.2K pullups.
The third is the reset into a 7406 input. I can probably disconnect that.

If I leave the pullups connected to the computer power, there's no
path from the wall wart power back into the computer????
Solves the problem? yes? no?

As soon as the portable scope charges up, I should have an answer to
whether
it works.
Click to expand...
Guess you missed my point. So how do you know you overloaded the 5V? Of
course we already know the keybord did not work. But did the 5V drop when
the keyboard was connected? I not, the new machine looks like to be able to
provide that 180mA.

As for the interface, I ever got a printer interface that was blown by just
the 7406 you mentioned. It was not a single accident but structural for that
series of PCs. The (CMOS) chip involved could not handle the 5V on the I/O
when the chip got no power. We may hope todays interfaces are able to handle
this but I'd not be too sure. So yes, there is a path from the wallwart into
the computer and it is through the pullups.

A second path may exist through the keyboards inputs. These inputs may be
74LS14 often used along with 7406 outputs. If so, the computers outputs will
"get" 5V even when not powered.

While working these outputs should be able to sink 0.4mA plus the current
through the pullups. So if the output is driven low but cannot sink enough
current, it may not go low enough to make the keyboard see it as a low.
(FAIK this is a possible cause for the problem not mentioned so far.)

Using a scope you'd be able to figure out not only the power levels but also
the shapes of the signals. I'd like to hear the results.

petrus bitbyter
 
On 7/12/2013 3:27 AM, petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:kro1ej$ucs$1@dont-email.me...
On 7/11/2013 3:52 PM, petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:krn0hb$53t$1@dont-email.me...
On 7/11/2013 9:45 AM, Michael Black wrote:
On Thu, 11 Jul 2013, dave wrote:

On 07/11/2013 02:58 AM, petrus bitbyter wrote:
"Michael Black" <et472@ncf.ca> schreef in bericht


Michael

If you modify that brandnew machine you will loose all guarantee.


Not in the USA. A computer is considered "open architecture" and can
be modified by the end user without voiding a warranty. "Reasonable"
modifications attendant to the "open architecture" modus operandi are
permissible.

The last "new" computer I bought was in 1989, so when I saw "new" I was
thinking it was actually a used computer new to the poster.

No, bypassing whatever current limiting there might be between the +5v
line and the keyboard is likely going to cause issues with warranty.
Of
course, that only matters if you need the warranty, ie the computer
fails and you want to send it back.

Michael

Well, I built the fixture and tested it.
Keyboard draws 180 mA.
New keyboard is less than 10mA.
BIOS date is 2008. Probably the result of some
GREEN initiative to save the world from abusive
keyboard power waste.

I really don't want to work on the motherboard.
It's already installed and a logistic nightmare.

I'm thinking about leaving the 2.2K pullup resistors
connected to the motherboard 5V and running everything else
in the keyboard
off a wall wart. I think that reduces the risk of
anything in the computer latching up and smoking when the computer or
keyboard is powered off.

That sound rational?

Er... No. So your old keyboard requires 180mA. Did it work correctly on
the
old machine that way? If so, can your new machine provide that 180mA?
*If*
not, *then* your solution makes sense *otherwise* its only a maybe.

From your information it is not clear on what conditions the keyboard
worked
all these years. If 5V/180mA does the trick and your new machine can
provide
it, lack of power is not the main problem. The 5V/180mA is not all that
bad.
In the old days the keyboards often were protected by a 1A fuse.

To check it out, you first connect the old keyboard to an old machine.
You
will find the required current. Suppose that's the 180mA. Now connect
your
new keyboard to the new machine. The 5V/10mA should do. Disconnect the
new
one and connect the old one. Now if the machine cannot provide the power
required you should find the 5V dropping. If not, the machine does not
seem
to have a problem providing the required current.

But if you new machine cannot provide enough power, your method is not
100%
save. Problems may arise when you shut down the computer while the
wallwart
is still going on. I ever found printer ports blown when the computer was
powered down before the printer. So to stay on the safe side I'd use the
10mA from the machine to active a small relay that switches the wallwart
power to the keyboard. Suppose there's plenty of space in the old
keyboard.

petrus bitbyter


INteresting...
I follow and agree with your troubleshooting procedure.
But, I have a guiding principle...never ask a question if the answer
won't change the future.
I already know the old keyboard won't work on the new computer.
Plugging it in again just overloads the 5V again. Possible harm, no help.

I believe I have only one option...power the keyboard externally.
That either fixes it or doesn't. That experiment is far easier than
disassembling the machine and trying to reverse-engineer the keyboard
interface.
The risk/reward ratio for messing with the motherboard is unfavorable.

I share your concern about backfeed and originally considered the relay.
But, the only things attached to the computer are two 7406 open-collector
outputs and 2.2K pullups.
The third is the reset into a 7406 input. I can probably disconnect that.

If I leave the pullups connected to the computer power, there's no
path from the wall wart power back into the computer????
Solves the problem? yes? no?

As soon as the portable scope charges up, I should have an answer to
whether
it works.

Guess you missed my point. So how do you know you overloaded the 5V?
Click to expand...
Actually, I don't. But if that's not the problem, I don't have any
other options. I can't do anything about the signal levels or the timing.

I just realized another possible option. As I recall, the keyboard
runs off the "always-on" auxiliary 5V supply. If that's got a problem,
that would explain why dragging down the keyboard power makes it refuse
to boot. That's relatively easy to check.
Of
course we already know the keybord did not work. But did the 5V drop when
the keyboard was connected? I not, the new machine looks like to be able to
provide that 180mA.

As for the interface, I ever got a printer interface that was blown by just
the 7406 you mentioned. It was not a single accident but structural for that
series of PCs. The (CMOS) chip involved could not handle the 5V on the I/O
when the chip got no power. We may hope todays interfaces are able to handle
this but I'd not be too sure. So yes, there is a path from the wallwart into
the computer and it is through the pullups.

A second path may exist through the keyboards inputs. These inputs may be
74LS14 often used along with 7406 outputs. If so, the computers outputs will
"get" 5V even when not powered.
Click to expand...
I tested it on a different computer.
The diode isolates the 5V, but the data line does have an input on it.
Worst case back into the computer is 1.6V. Short circuit currrent to ground
is under 2mA.
Keyboard works fine with or without the wall wart.
Now, to test it on the problem computer.


While working these outputs should be able to sink 0.4mA plus the current
through the pullups. So if the output is driven low but cannot sink enough
current, it may not go low enough to make the keyboard see it as a low.
(FAIK this is a possible cause for the problem not mentioned so far.)

Using a scope you'd be able to figure out not only the power levels but also
the shapes of the signals. I'd like to hear the results.
Click to expand...
I can't take this computer down till tonite, but I'll have more info later.
petrus bitbyter
Click to expand...
 
"mike" <ham789@netzero.net> schreef in bericht
news:krqonl$tq6$1@dont-email.me...
snip

Ok,
I got paranoid about the 5V standby supply and took the machine apart.
I had one power supply with a bad cap in the 5V standby switcher
and was letting 25V spikes thru. Wanted to verify that this
one didn't have that problem.

Turns out that the keyboard does not run off the 5V standby
supply.
And all the power supplies check out ok.
And the keyboard has 5V.
Adding the wall wart didn't help.

But it still wouldn't post.

I got distracted and discovered that the new computer
with the old keyboard does indeed boot after about a minute or so.
Also discovered by accident that if I press a key, the computer
will POST immediately.

I'd cut the reset wire, so I experimented with that.
If I press scroll lock, the light lights.
If I ground the reset pin, nothing happens.
Keyboard still working, light still on.
I infer that grounding the reset pin didn't reset
anything.

I put it all back together and called it done!

As luck would have it, I found a keyboard at a garage sale
today that I like pretty well. I miss the function keys
down the left side, but having F12 and right-control for
virtualbox is a plus. I'll play with that one for a while.

Thanks for the help.
mike
Click to expand...
Well, if you only have to hit a key to post I think the problem has been
solved.

I did not expect to reset line to be the cause but you had to check it.

I neither expected the 5V to be the cause anymore. Not after what you told
about it.

I also did not expect what you eventually found but I'm not astonished
either. At post, the BIOS looks for a keyboard by trying to communicate with
it. I suppose the old and relatively slow keyboard missed the initial
message and did nothing while the PC was waiting for a reaction until it
timed out.

I am astonished about the way you found the results at last. In my
experience operators (and other users) tend to hit the keyboard if nothing
seems to happen. Often hit it very hard.

petrus bitbyter
 
On 07/13/2013 9:36 AM, petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:krqonl$tq6$1@dont-email.me...
snip

Ok,
I got paranoid about the 5V standby supply and took the machine apart.
I had one power supply with a bad cap in the 5V standby switcher
and was letting 25V spikes thru. Wanted to verify that this
one didn't have that problem.

Turns out that the keyboard does not run off the 5V standby
supply.
And all the power supplies check out ok.
And the keyboard has 5V.
Adding the wall wart didn't help.

But it still wouldn't post.

I got distracted and discovered that the new computer
with the old keyboard does indeed boot after about a minute or so.
Also discovered by accident that if I press a key, the computer
will POST immediately.

I'd cut the reset wire, so I experimented with that.
If I press scroll lock, the light lights.
If I ground the reset pin, nothing happens.
Keyboard still working, light still on.
I infer that grounding the reset pin didn't reset
anything.

I put it all back together and called it done!

As luck would have it, I found a keyboard at a garage sale
today that I like pretty well. I miss the function keys
down the left side, but having F12 and right-control for
virtualbox is a plus. I'll play with that one for a while.

Thanks for the help.
mike


Well, if you only have to hit a key to post I think the problem has been
solved.

I did not expect to reset line to be the cause but you had to check it.

I neither expected the 5V to be the cause anymore. Not after what you told
about it.

I also did not expect what you eventually found but I'm not astonished
either. At post, the BIOS looks for a keyboard by trying to communicate with
it. I suppose the old and relatively slow keyboard missed the initial
message and did nothing while the PC was waiting for a reaction until it
timed out.

I am astonished about the way you found the results at last. In my
experience operators (and other users) tend to hit the keyboard if nothing
seems to happen. Often hit it very hard.

petrus bitbyter
Click to expand...
Interesting, may explain why the BIOS has a setting where it can ignore
the keyboard. Completely forgot about the POST interrogating the
keyboard part...

John :-#)#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
 
On 7/13/2013 10:46 AM, John Robertson wrote:
On 07/13/2013 9:36 AM, petrus bitbyter wrote:
"mike" <ham789@netzero.net> schreef in bericht
news:krqonl$tq6$1@dont-email.me...
snip

Ok,
I got paranoid about the 5V standby supply and took the machine apart.
I had one power supply with a bad cap in the 5V standby switcher
and was letting 25V spikes thru. Wanted to verify that this
one didn't have that problem.

Turns out that the keyboard does not run off the 5V standby
supply.
And all the power supplies check out ok.
And the keyboard has 5V.
Adding the wall wart didn't help.

But it still wouldn't post.

I got distracted and discovered that the new computer
with the old keyboard does indeed boot after about a minute or so.
Also discovered by accident that if I press a key, the computer
will POST immediately.

I'd cut the reset wire, so I experimented with that.
If I press scroll lock, the light lights.
If I ground the reset pin, nothing happens.
Keyboard still working, light still on.
I infer that grounding the reset pin didn't reset
anything.

I put it all back together and called it done!

As luck would have it, I found a keyboard at a garage sale
today that I like pretty well. I miss the function keys
down the left side, but having F12 and right-control for
virtualbox is a plus. I'll play with that one for a while.

Thanks for the help.
mike


Well, if you only have to hit a key to post I think the problem has been
solved.

I did not expect to reset line to be the cause but you had to check it.

I neither expected the 5V to be the cause anymore. Not after what you
told
about it.

I also did not expect what you eventually found but I'm not astonished
either. At post, the BIOS looks for a keyboard by trying to
communicate with
it. I suppose the old and relatively slow keyboard missed the initial
message and did nothing while the PC was waiting for a reaction until it
timed out.

I am astonished about the way you found the results at last. In my
experience operators (and other users) tend to hit the keyboard if
nothing
seems to happen. Often hit it very hard.
Click to expand...
If I plug in something new and the system won't POST, the very first thing
I do is pull the plug. Don't wanna let the smoke out.

I've had systems put up the BIOS splash screen and hang.
This was a new symptom for me.
petrus bitbyter



Interesting, may explain why the BIOS has a setting where it can ignore
the keyboard. Completely forgot about the POST interrogating the
keyboard part...
I'm pretty sure this bios doesn't have that. Would have been the first
Click to expand...
thing I checked.
Can't check while I'm typing this ;-)
John :-#)#

Yep, problem solved. Smoke still intact ;-)
Click to expand...
Thanks, mike
 
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