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my xt clone stopped recognizing the keyboard

redhawk579

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May 9, 2011
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new jersey
I have 2 keyboards both XT/PC keyboards they both to my knowledge work and today the bios reported to my despair a error:( so i tried everything I can find on the internet but none of it worked so i did more research and i found that it could be a blown keyboard connector fuse on the motherboard and i looked and sure enough there was one. what I am asking is is there a chance it could be blown and if so can I jump the connections or do i have to replace the fuse.
 
Hmmm, that's not usual kit for an XT clone. Still, just unplug the keyboard and measure the resistance across the fuse (with the system power off). If it's blown, it'll measure as an open circuit.

I'd do that before jumpering or replacing the fuse. If a fuse blows, it's usually for a reason.
 
Something else to investigate: Some XT clones have a keylock on the front panel, that disables/enables the keyboard. The keylock is connected to the motherboard via cable. On some make/models of motherboard, if the cable comes off the motherboard, the keyboard becomes disabled.

but I dont have a multimeter
The purchase of an inexpensive multimeter may be a good investment. With vintage computers, there invariably comes the time when one needs one.
 
from what i could see anyway

Yeah, you can't just "eyeball" most board problems... sure, sometimes there are obvious burn marks, but most failures are invisible component failures. It'll suprise you sometimes, I've had brand new shiny looking RAM chips that had failed, and nasty, filthy ones with corroded legs that worked fine.

Definitely check the keyboard fuse - it's not an uncommon failure. If you don't have a meter, now is as good as any time to buy one. You don't need to go all out and buy a fluke or something, an inexpensive $20 meter from Radio Shack will serve you well. If possible, spring for an autoranging meter, they're really handy.

-Ian
 
Definitely check the keyboard fuse - it's not an uncommon failure. If you don't have a meter, now is as good as any time to buy one. You don't need to go all out and buy a fluke or something, an inexpensive $20 meter from Radio Shack will serve you well. If possible, spring for an autoranging meter, they're really handy.

I'm not sure if autoranging (I use a Fluke 77, FWIW) is all that great, particularly in the hands of a novice. I find myself locking the range when doing serious work--I know what the reading should be and am looking for something unexpected. Autoranging just slows the process down. For almost all vintage work, a cheapie will probably be just fine. Save the money for a logic probe and some other useful tools.

But then, I cut my teeth on a Simpson 260. Still one of the finest analog meters around. Heck, I still own a working VTVM.
 
ill test it as soon as i can, but if it is blown should I jump it

Like Chuck already said: "If a fuse blows, it's usually for a reason." Fuses are there to protect something else. Jumping it will possibly allow that something else to burn up. If you're OK with that, then jump it. If not, then take a more diagnostic approach.
 
Nothing wrong with a penny under a blown fuse, is there, Ole? :)

Better to use a bullet...

Yes, I've seen the pennies, and even a wad of aluminum foil. I don't know about using bullets, but the old medium base flash bulbs that reporters used to use, would fit in a regular medium base lamp socket as well - much to the surprise of the person throwing the switch. (Let there be light!)

Actually, as we speak, I'm installing a new hot water tank. The old one would trip the breaker, and if you put the breaker back on, then the main, 100 Amp, breaker would trip. That's one hell of a load to dissipate. A penny would likely have caused a bit of a headache in this situation.
 
ok guys i got a multimeter, set it to ohms and got nothing meaning it is blown, what should my next course of action be?
 
Replace the fuse. But, I'd check your keyboards with the meter to make sure you don't have a short there - check between 5v and ground on the keyboard and make sure it's not real low. Something caused the fuse to blow in the first place. It's possible to blow it by plugging it in sloppily with the power on, or connecting something that's not a keyboard to the port. Or, a damaged keyboard can blow the fuse too.

-Ian
 
Got nothing? Meaning it read 0 or it read 1?
If 1, then yes, the fuse is blown. If 0, the fuse is good.
Chuck's "1" is better described as "no resistance measured" - the resistance is beyond the meter's ability to measure. The display that the meter shows for that condition varies between meters. For example, the Fluke brand multimeters display "OL".

So become familiar with your meter. The resistance of fuses varies a lot depending on a few factors. The motherboard fuse, if good, should measure somewhere between zero ohm and about 1 ohm.

Another way to check the keyboard fuse would be to:
1. Put your multimeter into 'DC voltage' mode, then
2. Connect the black probe to the metal case of the power supply, then
3. Connect the red probe first to one end of the fuse, noting the voltage showing on the meter.
4. Connect the red probe to the other end of the fuse, noting the voltage showing on the meter.

If both readings are 5 volts (or close), then the fuse is good.
If one reading is 5 volts (or close) and the other reading is 0 volts (or close), then the fuse is bad.
 
Chuck's "1" is better described as "no resistance measured" - the resistance is beyond the meter's ability to measure...
Sounds even more confusing to me; I'd think that "no resistance" means 0 Ohms (as in a piece of wire) whereas a "1" (or whatever the overrange indicator is) means a very large resistance was measured, too high for the current range.
 
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Sounds even more confusing to me; I'd think that "no resistance" means 0 Ohms (as in a piece of wire)
When I think about it now, I agree. Thank you for pointing that out.

whereas a "1" (or whatever the overrange indicator is) means a very large resistance was measured, too high for the current range.
I could see that Chuck's "1" could be misleading to people who are novices with multimeters. I can imagine a novice measuring a fuse at say, 1.1 ohms, and thinking to themselves, "Well, that is close enough to 1. The fuse must be blown."
 
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