Identifying weird resistor in faulty SMPS

[schenkzoola]

On the supply for the SLT/386, the green light flashes when plugged into the mains, but unplugged from the computer.  When plugged into the computer, the light immediately goes solid green.

[schenkzoola]

One thing that seems critical on these machines is to remove the old battery.  Apparently they fail short.

[schenkzoola]

I have an update!  I ran the laptop on this power supply (with the blinking LED when disconnected from the laptop) for about 90 minutes.  After that time, the power supply blinked off which caused the computer to shut down.  I could simply switch the computer off and on again, and it would run for a shorter amount of time.  Swapping in a supply from an SLT/286 allowed the computer to run indefinitely.

So it seems my power supply does have a thermal issue or something.

[badgerthing]

I have an update!  I ran the laptop on this power supply (with the blinking LED when disconnected from the laptop) for about 90 minutes.  After that time, the power supply blinked off which caused the computer to shut down.  I could simply switch the computer off and on again, and it would run for a shorter amount of time.  Swapping in a supply from an SLT/286 allowed the computer to run indefinitely.

So it seems my power supply does have a thermal issue or something.

Have you opened it? It almost certainly has leaking NCC caps on the secondary that will smell of cat pee.

[schenkzoola]

When I was troubleshooting the blinking light, which I thought meant it was faulty, I inspected the caps.  They were a pair of 470uF.  I measured the capacitance and dissipation factor.  Both tested similar to new caps so I put them back in.  No signs of leakage at that time.

I'll probably replace them next time I open it.  Perhaps they are temperature sensitive or something.

[badgerthing]

Since you have a working SLT/286 PSU, perhaps you could do what I intended to do, and document the pin functions. For this, you would need to make a new battery, as some pin functions may be related to battery charging, protection events, etc

[schenkzoola]

Yes I noticed that when I was inspecting the internal laptop PSU.  I have a spare removable cable, so I'll need to make up a quick breakout board for that 6 pin header to put between the laptop and the PSU.  I've got a couple other projects in the pipeline I need to do first, but it's on my list of things to do.

[schenkzoola]

Ok!

I've worked out enough of the pinout to get the laptop running with a third party power supply.  I don't have a good battery, so I wasn't able to really determine what the battery sense terminals do, or see what things look like when charging.

In the image you can see the pinout looking into the computer.  These are the male pins.

1) Battery Sense - I don't really know what this signal does, other than it is related to the battery
2) Battery Sense - I don't really know what this signal does, other than it is related to the battery
3) PS_ON - Connect this signal to ground to turn on the power supply.  The laptop doesn't care about this signal, only the power supply.
4) +18V - This is the main power feeding the laptop.  This is at about +6v when PS_ON is disconnected.
5) Voltage Sense? - I believe this is to compensate for voltage drop across the wiring.  When I disconnect this with the laptop powered, the voltage produced by the power supply increases slightly.
6) GND

I confirmed the computer will power with just 18V connected to pin 4, and 0V connected to pin 6, and all other pins open.  This was tested with an SLT/386 and a bench supply.