some keys not working on keyboard

This might be reposted in hardware forum...

I have a fairly specific computing environment (as we all do), and an issue...
The issue is with a PC (details below) and a keyboard, and possibly some other hardware....

First the symptoms seems like the 5, 6 -, and = keys are not working; nothing happens when they are pressed. This goes for those keys SHIFTed. Also, CNTL+ALT+DEL doesn't bring up the task manager, and CTRL+V doesn't paste. I think that's all but IDK how to exhaustively test a keyboard.
The keyboard is a Microsoft Wireless 700 v2.0 with associated USB receiver and wireless optical mouse. The mouse, receiver and most of the keyboard work ok it seems.It was acquired 'used' because I don't need the extra wires.

The wired PS/2 mouse and every wired keyboard have worked ok.

Sometimes, I have read, this is a software fault (reference available), but I am very conscious of it might be an electromechanical fault with the keyboard. How can I tell ? I do not want to take the keyboard if I can possibly avoid it. I did that once to another keyboard and it's still in pieces :-o

Dumb_Question
4.March.2015

HP Pavilion a405.uk - MSI MS-6577 v3.1 - Celeron 2.53GHz (Northwood) - 1GB RAM - 80GB WD HDD - Windows XP/SP3

 

Try the keyboard on another computer.

 

If the keyboard doesn't work on another PC, check the batteries.

 

-> Eldon
Check batteries was the first thing I did. I tried various pairs. None operated the dud keys reported I my first post in this thread. The dead pairs of batteries of course did not operate any of the keys.

->DOA
I have just tried the set-up on my Compaq Presario S5160UK, a very nearly identical model with the same (but more cluttered) O/S [WinXP Home 32 bit], more RAM, very slightly different processor, even less slightly different m/b, with identical results.

I have read (I learned) recently that it is possible to lift individual keys off the k/b from the top without disassembly the unit.

I would also point out, though I'm sure everyone is aware of this the affected keys occur in a kind of group or pattern, two pairs each comprising two adjacent keys, everything in the same row. Could this behavior be the result of a carefully though cosmetically cleaned up liquid spill ? The two pairs are quite far apart.

MS also say that drivers for this equipment are the same drivers for standard k/b and mice included as part of the O/S.

What's next DOA, Eldon, anyone ?

Dumb_Question
7.March.2015
(problems with an MS 700 "Desktop" k/b & mouse v2.0)

 

It's almost certainly the keyboard itself. Lifting the keys individually is not recommended. I would carefully disassemble the keyboard. The liquid spill may have created a shortcut. Carefully clean the 'rubber mat' with a damp cloth.

FYI I have twice disassembled my 10-year old keyboard, and then washed the top halve where the keys are clipped in with dishwashing liquid and water. I left it to dry for a day.

 

Hi,

I have taken the k/b apart; 12 cross head screws removal (haven't lost one yet !)

Inside there are two transparent sheets with printed circuits on them, lowermost appears to connect lines to keys, above that what appears to be a cross-cross grid (diagonal) tracks about 6mm ? apart all of which are connected to each other and to the earth track around the outside of that layer. These layers are joined in the middle by a tiny spot of glue (or a punch-through) in two places. They both appear very clean (under x10 jeweller's loup), with no material to be seen or other defects. I looked especially carefully around the affected keys area. Another thing I noticed was a short length - about 1cm - of the outer earth track on the appeared discoloured (dark brown instead of a yellowy colour) as though it had been oxidized and in one place even burned a little. I am not able to take suitably mag. pictures of all this. However, this was on the second layer not the lowermost (key interconnect) layer and I could not see how this might affect anything.

I gave the upper surface of the middle layer (2nd up) a wipe with a damp cloth, which incidentally did not appear to do anything to the discoloured track section. This the only surface aside from the k/b membrane, which could possibly have been contaminated.

The rubberized key membrane (I refer to it as a membrane, . I'm sure you know what I mean) layer sits above these the printed circuit layers and cushions the pressures of individual keys. Above this membrane, when the keyboard is right way up as in normal use, are the keys, to give you a clear idea of the order of the layers involved. The two printed circuit layers, on what appeared to be clear acetate sheets, came away with the bottom of the k/b and the membrane came away with the top side including the keys.

I would say there was no evidence of spillage of anything on that keyboard, not even water. In fact I could see no reason for any malfunction. I did not unscrew the little ciruit board clamping the lower printed circuit layers in place (which was perhaps my mistake with keyboard which has been in bits for more than 10 months)

More when (if) I reassemble k/b and test.

Dumb_Question
8.March.2015