ColTom2 said:
Hi:
I have a Sony VGC-RA716G desktop computer running XP MCE(2006) SP3 with
PS-2 cable for keyboard. The PS-2 connector on the end of the cable got bent
and is now defective.
Is there anyway to replace the PS-2 Connector (6 pin) at the end of the
keyboard cable? If not can the cable with PS-2 connector be replaced or do I
need to replace the entire keyboard? It's a somewhat special Sony keyboard
that came with the computer.
Thanks,
ColTom2
To make a repair, you'd start by preparing documentation for yourself.
I'm assuming the connector is still connected to the cable. Using a multimeter
set on ohms, you open the keyboard and "buzz" from one wire contact, until you
find which pin that corresponds to. So if there were four contacts
on the keyboard PCB, you'd buzz from there ("check for zero ohm reading"),
to a connector pin. A zero ohm reading, means there is a straight piece of wire
from the contact inside the keyboard, to that particular pin on the connector.
This requires disassembly of the keyboard, so you can get at the spot where the
cable is soldered to the keyboard.
Your keyboard should only be using four pins of six possible (+5V, GND, DATA, CLOCK).
There is a diagram here.
http://en.wikipedia.org/wiki/PS/2_connector
The ones that are important to connect correctly, are the +5V and GND. If you set
your multimeter to volts, and measured the appropriate four active pins
on the computer end, three of the four pins would read 5 volts. The power supply pin
is 5V. But both the clock and data, when idle, are pulled up to 5 volts via pullup
resistors. This is open collector logic, at least as shown on the following information
page. So doing a volts check on the computer end, could lead to confusing results.
In other words, you might not be able to rely on a voltage reading while things
are powered, to figure stuff out.
http://www.computer-engineering.org/ps2protocol/
So it really depends right now, on how "damaged" that connector is. If all
the pins are squashed together (a steam roller ran over it), then preparing
your documentation is not going to be that easy.
If the PCB inside the keyboard is clearly labeled as to which pin is which,
then your job is now a lot easier. Preparing your own documentation, is reserved
for those cases where every bit of your project is a "secret" they don't want you
to know. I doubt very much there is labeling. Using the multimeter to buzz out
the wiring, is how you'd prepare your own documentation, so you can mark
the four contacts on the keyboard PCB (+5V, GND, DATA, CLOCK).
It would be nice, if there were standard colors for the signals, but I don't know
if anyone would bother with that or not. After all. the cable is normally fully
covered with insulation, so there is no reason for color keying inside.
As for your repair materials, I was hoping to find a "captive cable" replacement,
but I couldn't locate one of those. (That would have the PS/2 miniDIN on one end,
and wires coming out the other end. You'd solder the wires to the PCB of the
keyboard.) If the keyboard had a non-captive cable, then you'd simply unplug the
old cable.
You can take a keyboard extension cable, snip the head off one end (leaving the
right kind of connector on the other end). Then strip the appropriate four
wires (using your "buzzing" skills, to map cable color to pins on the cable),
and then you'd be able to solder the replacement cable in place. Since the
cut end of the cable is now hidden inside the keyboard, you get a nice neat job.
Usually, the keyboard will have some mechanism for strain relief, and you'd duplicate
how the old cable was installed. The idea is, either plastic fingers grip the cable
and prevent it from being pulled out of the keyboard, or in some cases a loop or
knot is formed in the wire, to prevent it from being pulled out.
In terms of repair materials, you'd need.
1) Multimeter. Should be able to measure volts and ohms. Current
measurement on cheap multimeters is hardly ever used.
2) 25 to 35W soldering iron. Better to err on the high side, so you have
enough heat. The +5V and GND wires might be a bit harder to solder and
unsolder, if there is a lot of copper plane at the solder point. A soldering
iron with a grounded tip is sometimes used for better electrostatic discharge
protection. The largest iron I have in my collection is 80 watts, and
if I'm having problems removing old solder, that one helps. If you
go for something like a 15W iron, there is virtually no chance your
project will ever get finished. I don't know why Radio Shack sells stuff
like that.
The old style "solder gun" with the penlight bulb to light up the
work area, is not recommended. I used to have one of those, and you
have to be careful not to exceed the duty cycle. (Work for 1 minute,
let the gun cool off for 5 minutes. Too much trigger pulling and
the transformer inside overheats.)
3) Solder wick. 0.050" wide wick might be used to soak up the old solder,
where the wires go into the PCB. The larger the wick, the more heat it
takes to get it to wick up the solder. Better to use thinner wick, than
thicker stuff. So 0.050" or 0.025" might work, nothing larger.
(This is what is in my toolbox right now, for super fine work.)
http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=6610190&MPN=423
You can use diagonal cutters, to ship off the old cable. Then all you're
left with, is a small bit of wire and the holes to clean out.
4) "Electronic" solder, not plumbing ("acid core") solder. Electronic solder
uses a resin core flux, and resin cleanup is possible with various alcohols.
I have a one pound roll of solder which is smaller diameter than this
(angel hair). This is better than nothing (or better than plumber's solder).
I notice Radio Shack sells plenty of stuff you should not be using.
http://www.radioshack.com/product/index.jsp?productId=2062713
5) Wire strippers. Many times, you can find the yellow handled ones at the
hardware store. They're better than using your teeth to strip the insulation
off the wire. At the other extreme, there are automated strippers, where the
stripping action is more fully controlled, and those won't nick the wire strands
by accident. The cheap stripper from the hardware store, would require a lot of
practice, to get a clean strip without nicks. You need to examine the lengths
of bare wire on the existing captive cable, to figure out how long to make
each one on your replacement cable.
Sounds like loads of fun if you've never soldered before.
HTH,
Paul
