A2000 R914 resistor (keyboard problem)

[duga]

Hi

So, I have this A2000 with a sporadically working keyboard. Some keys never work, some work sporadically. Caps lock blinks once at power up.

My theory right now is that the R914 is the cause of this issue, with the help of http://home.arcor.de/kickstart/TKA/Tutorials/troubleshooter/trouble2.html and other sites.

Before the resistor I have 4.97 Volt, after the resistor I have between 1-3 Volt as it differs a lot.

Problem: I only have 0.25 W resistors but no 0.5 W resistors. Any suggestions for a replacement resistor? It should be 1 Ohm, 0.5 Watt according to the mentioned site but as I said I only have 0.25 Watt resistors.

[mechy]

No offense, but this seems like a no brainer.. Just buy the correct resistor and replace it
they should be available at any electronics supply store.

If you are in the usa, try mouser,digikey or such.

[fjudde]

If you have two 2ohm resistors you can attach them in parallel, That will result in a 1ohm/0.5w resistor. If you have the physical space for it, and the soldering skills of course.

[duga]

No offense, but this seems like a no brainer.. Just buy the correct resistor and replace it
they should be available at any electronics supply store.

If you are in the usa, try mouser,digikey or such.

Here in Sweden what you find on a Sunday (at Kjell & Co or Clas Ohlson) is mostly 0.25W resistors in big packs. I already have that.


I changed the capacitor C912 as I had one with the right specs, didn't make any difference.

[duga]

If you have two 2ohm resistors you can attach them in parallel, That will result in a 1ohm/0.5w resistor. If you have the physical space for it, and the soldering skills of course.

Thanks, but I only have 0.25W.

[mechy]

Thanks, but I only have 0.25W.

he meant if you have 2-2ohm .25w resistors,you can parallel them to make 1ohm .5w

[duga]

Aha. No, nothing smaller than 7.68 Ohm 0.25 Watt here unfortunately.

[guest11527]

So, I have this A2000 with a sporadically working keyboard. Some keys never work, some work sporadically. Caps lock blinks once at power up.

My theory right now is that the R914 is the cause of this issue.

Did you measure the resistor? For that, unplug the keyboard, turn the computer off, and measure it with a multimeter. One of its two connections is now dangling, so there is no current going into any other components of the system.   Rather, if the voltage dropped by so much on its end, it could instead indicate a short in the keyboard itself. For that, test with a known to be good keyboard from a second system.

[duga]

I don't have another keyboard to test with nor another A2000/A3000 to test this keyboard on.

I measured it while running, both with and without the keyboard. I don't get what you mean by "turn the computer off, and measure it with a multimeter".


I should probably mention that (of course) there has been a battery leakage. Battery is removed. Have seen much worse damage than this though.

[som99]

Why not just order one from elfa.se, you will get it within two days.

[Oldsmobile_Mike]

I don't have another keyboard to test with nor another A2000/A3000 to test this keyboard on.

I would really test with a different keyboard before you start hacking your motherboard apart. eBay, man.

[guest11527]

I measured it while running, both with and without the keyboard. I don't get what you mean by "turn the computer off, and measure it with a multimeter".

There's a switch in the back of the computer. Turn that to the *off* position. Unplug the keyboard. Also unplug the power cord from the system. Open the system. Locate the resistor. Switch the multimeter to "Ohm", written as a big omega. Connect one wire of the multimeter to one end of the resistor, connect the other wire to the other end. What do you read?

I should probably mention that (of course) there has been a battery leakage. Battery is removed. Have seen much worse damage than this though.

Then apparently there is more damage than you assume. Really. That's a number one reason why strange things happen. Just changing the resitor will not provide much. Keyboard power and wiring is pretty much in the same position as the real-time clock, namely in the front-right position of the board.

In that case, remove the board completely and clean carefully, inspect all wires. It wouldn't surprise me the least if some of the connections seem to look good at first inspection, but fail to connect properly because they were corroded by the battery.

[duga]

There's a switch in the back of the computer. Turn that to the *off* position. Unplug the keyboard. Also unplug the power cord from the system. Open the system. Locate the resistor. Switch the multimeter to "Ohm", written as a big omega. Connect one wire of the multimeter to one end of the resistor, connect the other wire to the other end. What do you read?




Then apparently there is more damage than you assume. Really. That's a number one reason why strange things happen. Just changing the resitor will not provide much. Keyboard power and wiring is pretty much in the same position as the real-time clock, namely in the front-right position of the board.

In that case, remove the board completely and clean carefully, inspect all wires. It wouldn't surprise me the least if some of the connections seem to look good at first inspection, but fail to connect properly because they were corroded by the battery.

Thanks. It reads, after "jumping" for a while, 14 M ohms. Yes, 14 M ohms. Not 14 K ohms or 14 ohms.

[fjudde]

Thanks. It reads, after "jumping" for a while, 14 M ohms. Yes, 14 M ohms. Not 14 K ohms or 14 ohms.

That's a very high value! time for replacement! Try to find 1W or higher instead of .5W. It will hopefully prevent the resistor from running to hot and eventually fail.

If you can't find any soon enough and if you have att least four (4) 1 Ohm/.25W resistors you can build your own 1 ohm/1W.

2 in parallel gives you .5 Ohm/.5W

another 2 in parallel gives you another .5 Ohm/.5W

Now put these two 0.5 Ohms in series with each other and you get 1 ohm/1W.

[guest11527]

Thanks. It reads, after "jumping" for a while, 14 M ohms. Yes, 14 M ohms. Not 14 K ohms or 14 ohms.

That's more like the resistance of your body, from one hand to another. With that resistance, the keyboard would be completely inoperable, not "half way broken". Hence, your meter did not make contact with the resistor properly. It *does* supply *some* current to the keyboard, after all, and for that, 14 M Ohms is way, way, way, way too large.