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486 motherboard key lock stuck

D

DamienC

Experienced Member
Joined
Aug 2, 2010
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72
Location
Southern NJ USA
I'm testing a bunch of old motherboards before I get rid of them. I managed to get a Lucky Star LS-486E 486 board to post (after I thought I killed it years ago). One problem though is that after it POSTs, it complains of a key lock being blocked closed and I can't continue because I can't hit F1.

I have nothing on the key lock jumper on the board, and there isn't one in the case because I'm using an ATX case & PSU.

I know pin 1 is 5V for an LED, pin 4 is the keylock, and the other 3 pins are grounds. I tried shorting the key lock pins to all the grounds and that did nothing. Is there any way to disable the keylock altogether? Removing the CMOS battery does nothing.
 
DamienC said:
I know pin 1 is 5V for an LED, pin 4 is the keylock, and the other 3 pins are grounds.
Click to expand...
Back in 2010, when you were dealing with this motherboard, you discovered: "It turns out the bus speed jumpers listed in the manual were labeled backwards!"
So, could your information about the keylock related pins be wrong too ?
 
modem7 said:
Back in 2010, when you were dealing with this motherboard, you discovered: "It turns out the bus speed jumpers listed in the manual were labeled backwards!"
So, could your information about the keylock related pins be wrong too ?
Click to expand...

I checked with a multimeter. 5V on pin 1, nothing on 2-5. Something tells me pin 4 should have something.
 
If you are measuring +5V on pin 5, then potentially (pun intended), you could be measuring the end of a pull-up resistor.
With no current flowing through the resistor, both ends of the resistor will measure +5V.
So maybe the following is the situation.

http://www.minuszerodegrees.net/images4/pullup_resistor.jpg

But before you try shorting pin 5 to ground, you should first verify that pin 5 isn't directly connected to the +5V line (otherwise you will be shorting out the +5V).
With power off, measure the resistance between pin 5 and +5V.
If you measure zero or a few ohms, then you should consider pin 5 to be a +5V line.
 
CN14 is the turbo LED. CN12 is definitely the keylock.

I'm reading about 125 ohms between pin 1 and pin 5 of CN12.

I've seen on a lot of boards that the power LED goes into pins 1-3 and the keylock goes into 4-5. Not sure if it's relevant here but I thought I'd mention it.
 
There was no standard pinout and so I think that comparison with other boards is risky.

The board's user manual has CN12 shown as 'KEYLOCK', not 'KEYLOCK AND POWER LED'. But of course, manufacturers do make documentation mistakes. If CN12 is only for attachment of a KEYLOCK connector, then it does seem odd that CN12 has 5 pins when only two are required, however, look at the typical speaker connector - 4 pins when only two are required.

So what about a power LED. Some motherboards did not have a connection point for that, the LED being connected to the turbo unit instead. (Example [here].)

DamienC said:
I'm reading about 125 ohms between pin 1 and pin 5 of CN12.
Click to expand...
You need to measure between pin 5 and a known +5V line.
 
modem7 said:
You need to measure between pin 5 and a known +5V line.
Click to expand...

Pin 1 is a +5V line. Also measured between the +5V from the Turbo LED and from the Turbo Switch. Same reading.

Ah well. I kind of gave up on the board at this point. I'm probably just going to recycle it.
 
DamienC said:
Ah well. I kind of gave up on the board at this point.
Click to expand...
This is solvable.

DamienC said:
Pin 1 is a +5V line.
Click to expand...
Sorry. You did write that earlier. I'm getting confused.

If I was in your situation, what I'd be doing is identifying each pin as follows, because measuring voltage can be misleading:

1. With power off, if the pin has zero ohms (or less than 1 ohm) to ground, then the pin should be considered a ground pin.
2. With power off, if the pin has zero ohms (or less than 1 ohm) to a known +5V line (e.g. on PSU connector), then the pin should be considered a +5V pin.
3. With power off, if the pin has zero ohms (or less than 1 ohm) to a known +12V line (e.g. on PSU connector), then the pin should be considered a +12V pin.
4. With power off, if the pin has has no resistance to either ground/+5V/+12V, then the pin should be considered 'not connected'.

A pin that is not identified as either ground, +5V, or +12V, and has resistance to either of the three, probably has a purpose.
 
My 286 requires that the keylock pins are closed before the keyboard will work, the only irritating thing with this is that it doesn't match the markings on the front of the case.

Of course it is probably wise to make sure you won't be shorting anything you aren't supposed to before trying this.
 
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