16 Sep
2014
16 Sep
'14
10:59 a.m.
Trying to help out a friend, he's unable to get the mouse working on his
Amiga 2000. We've determined that the +5V line(s) on the DB-9 controller
ports are dead, which would tend to account for the non-working mouse. That
is, I assume the mouse electronics draw their power from the +5V pin.
So the +5 pin on each of the two ports lead back to a common point, which
is a fuse.. thing is, it's a surface-mount fuse, and it's marked 4A.. as in
FOUR AMPS.
Now the schematics we have do show the fuse, I believe it's indicated as
F1. But there's no rating on the diagram. Can anyone confirm that this is
actually a 4A fuse? Why on earth would they have such a high-rated fuse
protecting those lines?
What sort of controller-port peripheral device could ever need that much
current - and is a common DB-9 connector (or for that matter, the PC board
traces) even capable of that kind of current?
400mA maybe?
16 Sep
16 Sep
3:34 p.m.
0.4 amps fuse
---
Enviado do meu Apple IIGS (pq eu sou chique)
Meu site: http://www.tabalabs.com.br
Meu blog: http://tabajara-labs.blogspot.com
----- Original Message -----
From: "drlegendre ." <drlegendre at gmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Tuesday, September 16, 2014 3:59 PM
Subject: Amiga 2000 controller port fuse strangeness
Trying to help out a friend, he's unable to get
the mouse working on his
Amiga 2000. We've determined that the +5V line(s) on the DB-9 controller
ports are dead, which would tend to account for the non-working mouse.
That
is, I assume the mouse electronics draw their power from the +5V pin.
So the +5 pin on each of the two ports lead back to a common point, which
is a fuse.. thing is, it's a surface-mount fuse, and it's marked 4A.. as
in
FOUR AMPS.
Now the schematics we have do show the fuse, I believe it's indicated as
F1. But there's no rating on the diagram. Can anyone confirm that this is
actually a 4A fuse? Why on earth would they have such a high-rated fuse
protecting those lines?
What sort of controller-port peripheral device could ever need that much
current - and is a common DB-9 connector (or for that matter, the PC board
traces) even capable of that kind of current?
400mA maybe?
4:15 p.m.
How are you going to charge an iPad with that?
On Sep 16, 2014, at 6:34 PM, Alexandre Souza <alexandre.tabajara at gmail.com>
wrote:
0.4 amps fuse
---
Enviado do meu Apple IIGS (pq eu sou chique)
Meu site: http://www.tabalabs.com.br
Meu blog: http://tabajara-labs.blogspot.com
----- Original Message ----- From: "drlegendre ." <drlegendre at
gmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
Sent: Tuesday, September 16, 2014 3:59 PM
Subject: Amiga 2000 controller port fuse strangeness
Trying to help out a friend, he's unable to
get the mouse working on his
Amiga 2000. We've determined that the +5V line(s) on the DB-9 controller
ports are dead, which would tend to account for the non-working mouse. That
is, I assume the mouse electronics draw their power from the +5V pin.
So the +5 pin on each of the two ports lead back to a common point, which
is a fuse.. thing is, it's a surface-mount fuse, and it's marked 4A.. as in
FOUR AMPS.
Now the schematics we have do show the fuse, I believe it's indicated as
F1. But there's no rating on the diagram. Can anyone confirm that this is
actually a 4A fuse? Why on earth would they have such a high-rated fuse
protecting those lines?
What sort of controller-port peripheral device could ever need that much
current - and is a common DB-9 connector (or for that matter, the PC board
traces) even capable of that kind of current?
400mA maybe?
5:02 p.m.
Alex,
On Tue, Sep 16, 2014 at 6:34 PM, Alexandre Souza <
alexandre.tabajara at gmail.com> wrote:
0.4 amps fuse
400mA makes a lot more sense than 4A.. but may I ask what your source is?
----- Original Message ----- From: "drlegendre ." <drlegendre at
gmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts" <
cctalk at classiccmp.org>
Sent: Tuesday, September 16, 2014 3:59 PM
Subject: Amiga 2000 controller port fuse strangeness
Trying to help out a friend, he's unable to get the mouse working on his
Amiga 2000. We've determined that the +5V
line(s) on the DB-9 controller
ports are dead, which would tend to account for the non-working mouse.
That
is, I assume the mouse electronics draw their power from the +5V pin.
So the +5 pin on each of the two ports lead back to a common point, which
is a fuse.. thing is, it's a surface-mount fuse, and it's marked 4A.. as
in
FOUR AMPS.
Now the schematics we have do show the fuse, I believe it's indicated as
F1. But there's no rating on the diagram. Can anyone confirm that this is
actually a 4A fuse? Why on earth would they have such a high-rated fuse
protecting those lines?
What sort of controller-port peripheral device could ever need that much
current - and is a common DB-9 connector (or for that matter, the PC board
traces) even capable of that kind of current?
400mA maybe?
17 Sep
17 Sep
2:03 a.m.
On Tue, Sep 16, 2014 at 01:59:36PM -0500, drlegendre . wrote:
[...]
Now the schematics we have do show the fuse, I believe
it's indicated as F1.
But there's no rating on the diagram. Can anyone confirm that this is
actually a 4A fuse? Why on earth would they have such a high-rated fuse
protecting those lines?
I went and looked at the schematics of a few other Amiga models to see how the
mouse/joystick ports are implemented. For all but one of the models I checked,
pin 7 of both joystick/mouse ports are commoned and are connected to +5v via an
unmarked fuse. So that's not much help.
We hit the jackpot with the A500 though: each pin 7 is connected separately to
+5v via a 4R7 current-limiting resistor. Ohm's Law tells us that it limits the
short-circuit current to 1A, but since this would mean dumping 5W into what is
probably a 0.5W resistor, what you effectively have there is a fuse that makes
a nasty stench when it blows.
What sort of controller-port peripheral device could
ever need that much
current - and is a common DB-9 connector (or for that matter, the PC board
traces) even capable of that kind of current?
400mA maybe?
The 4R7 effectively limits it to 100mA per port, so I'd be tempted to go even
lower than that to ~200mA. Further, a resettable fuse is cheap[0] and will save
you having to wave the soldering iron the next time the port is shorted out.
[0] Farnell are listing suitable fuses for under 50p.
7:23 a.m.
That's good work, Peter. What you wrote makes perfect sense.. thank you!
The PSU in the A2000 is going to be quite a bit more substantial than that
in the A500 - IIRC, the A500 used a large-ish 'brick' supply like the
C-128, something on the order of 50W total output. Between the much larger
motherboard and all of the available expansion slots, the A2000 is going to
need several times that.
I think it's safe to say that they didn't mind 200-400mA being sucked out
of the A2000 controller ports, if need be. We'll probably stick with a
fuse, reset-able or otherwise.
On Wed, Sep 17, 2014 at 5:03 AM, Peter Corlett <abuse at cabal.org.uk> wrote:
On Tue, Sep 16, 2014 at 01:59:36PM -0500, drlegendre .
wrote:
[...]
Now the schematics we have do show the fuse, I
believe it's indicated as
F1.
But there's no rating on the diagram. Can
anyone confirm that this is
actually a 4A fuse? Why on earth would they have such a high-rated fuse
protecting those lines?
I went and looked at the schematics of a few other Amiga models to see how
the
mouse/joystick ports are implemented. For all but one of the models I
checked,
pin 7 of both joystick/mouse ports are commoned and are connected to +5v
via an
unmarked fuse. So that's not much help.
We hit the jackpot with the A500 though: each pin 7 is connected
separately to
+5v via a 4R7 current-limiting resistor. Ohm's Law tells us that it limits
the
short-circuit current to 1A, but since this would mean dumping 5W into
what is
probably a 0.5W resistor, what you effectively have there is a fuse that
makes
a nasty stench when it blows.
What sort of controller-port peripheral device
could ever need that much
current - and is a common DB-9 connector (or for that matter, the PC
board
traces) even capable of that kind of current?
400mA maybe?
The 4R7 effectively limits it to 100mA per port, so I'd be tempted to go
even
lower than that to ~200mA. Further, a resettable fuse is cheap[0] and will
save
you having to wave the soldering iron the next time the port is shorted
out.
[0] Farnell are listing suitable fuses for under 50p.
3580
days inactive
3581
days old
5 comments
4 participants
participants (4)
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abuse＠cabal.org.uk -
alexandre.tabajara＠gmail.com -
drlegendre＠gmail.com -
ryan＠hack.net