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Adapter pinout for Data General 450C laptop

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zevon8

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Hi .. does anyone know what the pinout is for the DC adapter for a Data General 450C laptop. It also has model # 760C on the bottom, and I believe it may be an Acer by that model number. The plug is a PS2 keyboard style plug, but with 3 pins. My research has only yeilded the following: 5.5VDC @ 3.5A and 8.8VDC @ 2.75A . I would like to resurrect the old beast for a project I have in mind, and don't want to replace the nicad pack because of the cost compared to using a small SMPS.

( it is alot of work to open it to the point where I could trace the power jack, it is truely buried )

Thanks!
 
The following method may or may not help you. This is how I determined the connections in a similar setup.

using a Ohmmeter you should be able to determine which pin is common or zero by measuring between another port for headphone etc.

Then according to the diagram if you apply an external variable voltage through a resistor to one of the pins, you would expect the 8.8V circuit to have higher impedance and the 5.5v lower according to the current ratings. The diode's may or maybe not in the unit for reverse polarity protection.

If you could power up the laptop via its battery this setup could also work as you might be able to monitor at what voltage's the lines start to draw current taking to account the diode drops.

It worked for me. After making my choices I powered up from a dual power supply with current limit, watching closely the current as I increased the voltage. I would start with both at 5-5.5V and adjust up VERY slowly watching the meters. If you have the 2 mixed up the (lower) one should increase current more for a slight voltage increase.
 

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Thanks, TheOne, good ideas, will give it a go.

I first thought, well this should be pretty easy, 3 pins, two voltages, one should be ground, so the rest easy. Unfortunately.. none of the pins really show low impedance to the shields or grounds on the rest of the laptop, and weird combinations of capacitor charge up between each other. Only one pin shows what seems to be a diode in series with the outer shield on the power jack.

If all else fails..it may be time to get out the ice-cube tray and the JIS screwdrivers!
 
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