Need advice rewiring jack to new power supply

Thread Starter

Myronaz

Joined Jan 3, 2018
32
Hello,

Recently, I found an old MS-DOS laptop from the 80s, which to make a long story short, took ALOT of work to restore back to working condition, finally, when I was done, the charger, decided to just die, simple as that, it... just... died... it has an LED indicator, which no longer lights up, worst part is the jack port is unique to the laptop, it's proprietary, and it has 8 pins just for power, no data, just power, luckily I was smart enough to map what each pin puts out as soon as I noticed it was proprietary

Here is the best schematic I could make out of the jack:


As can be seen, it seems that there are a few different power rails here, which is kind of weird for a laptop power jack, so how do I even rewire this to another power supply with only two power rails? (+ and -) do I stick the positive wires to a single positive rail on the newer charger, and negative rails to the negative single rail of the new charger? is that a good idea?
Also if you notice the schematic, Pin6 seems to have no connection, perhaps it was meant to be connected to the yellow wire but lost connection due to flex based damage?

Advice is very much appreciated, thank you
 

wayneh

Joined Sep 9, 2010
16,114
As can be seen, it seems that there are a few different power rails here, which is kind of weird for a laptop power jack, so how do I even rewire this to another power supply with only two power rails? (+ and -) do I stick the positive wires to a single positive rail on the newer charger, and negative rails to the negative single rail of the new charger? is that a good idea?
Without really knowing anything more than what you've shown, that's what I'd do. Have you searched around for details of your computer model? You might be able to even find a service manual that would explain that connector. That manufacturer may have also used it in other models that year. If you really want to reduce the risk of a surprise, the research would be worth it.

A modern laptop brick is usually more like 19V but I doubt that slight extra voltage is a concern. You could add a couple diodes in series to drop it down. If you do, just be sure they are rated for more than the max current drawn by the computer. A 1A rating is not likely enough, and 5A should be fine.
 

Thread Starter

Myronaz

Joined Jan 3, 2018
32
I did, it's a Mitac laptop, Mitac itself has very little information online, let alone one of their laptops from the 80s, I actually happen to have another desktop model from the same company, but again, little or no information at all! I really wanna get it working because it took a heck of alot of work to literally drill into one of it's chips and expose some battery terminals for CMOS, honest nightmare!

You mentioned something about amps, does that matter? It's rated for 1,97A but I heard that it doesn't matter because unlike voltage, amps are consumed as needed, not in a fixed rate, the charger i'll use is rated for 19v, 3,45A

I also thought about feeding it power through the battery terminals, since there is only two wires in the battery terminals, so there is much less risk of getting polarity or something else wrong, but when it comes to the battery, its rated for 9V, so connecting the charger there is an extra 10v, I do believe that this is a bit too much, the battery is NiCAD and is long dead, so really, if I could do that, I would drill a small hole in the case, solder a barrel jack and wire it to the inner battery terminals
 

djsfantasi

Joined Apr 11, 2010
5,701
I did, it's a Mitac laptop, Mitac itself has very little information online, let alone one of their laptops from the 80s, I actually happen to have another desktop model from the same company, but again, little or no information at all! I really wanna get it working because it took a heck of alot of work to literally drill into one of it's chips and expose some battery terminals for CMOS, honest nightmare!

You mentioned something about amps, does that matter? It's rated for 1,97A but I heard that it doesn't matter because unlike voltage, amps are consumed as needed, not in a fixed rate, the charger i'll use is rated for 19v, 3,45A

I also thought about feeding it power through the battery terminals, since there is only two wires in the battery terminals, so there is much less risk of getting polarity or something else wrong, but when it comes to the battery, its rated for 9V, so connecting the charger there is an extra 10v, I do believe that this is a bit too much, the battery is NiCAD and is long dead, so really, if I could do that, I would drill a small hole in the case, solder a barrel jack and wire it to the inner battery terminals
First, you’re right about the device drawing what it needs. But if it needs more than the charger can supply... oops. It won’t work.

And connecting to the battery terminals is a bad idea. First, by bypassing the charger jack, you run the risk of also bypassing important power circuitry. Like power management.
 

wayneh

Joined Sep 9, 2010
16,114
You mentioned something about amps, does that matter? It's rated for 1,97A but I heard that it doesn't matter because unlike voltage, amps are consumed as needed, not in a fixed rate, the charger i'll use is rated for 19v, 3,45A
Yup, you're right and that will be fine as long as the 19V is fine.
I also thought about feeding it power through the battery terminals, since there is only two wires in the battery terminals, so there is much less risk of getting polarity or something else wrong, but when it comes to the battery, its rated for 9V, so connecting the charger there is an extra 10v, I do believe that this is a bit too much, the battery is NiCAD and is long dead, so really, if I could do that, I would drill a small hole in the case, solder a barrel jack and wire it to the inner battery terminals
I wouldn't put anything other than 9V there.
 

Thread Starter

Myronaz

Joined Jan 3, 2018
32
Got an update, found the time to try this today, and at first, It didn't work, so I panicked thinking I must of have got polarity in one of the pins wrong while taking the schematic, it's easy to make a mistake with so many pins, and also the light on the charger would turn off if I inserted the jack to the laptop and turn back on when I removed it

So... with some hope I left I started cutting wires, I first took out the cyan wire (negative), thinking this is too bright of a colour code to be negative, didn't really have much else to go on, same result, then I took out the purple wire (positive) and immediately the light on the charger came back on and the laptop turned on!!!!!! so not really sure what happened there but I sure hope it wasn't wrong polarity because although it survived it, I've seen circuits showing effects of damage after days, I had a circuit that took reverse polarity, survived but the polarized electrolytic cap started leaking a few days after

Im not really sure what to make of this, or if I should get greedy and try to connect those two wires but on reverse this time, the laptop seems to be powering on fine so not really sure that its worth the risk, besides its just a 386 machine, so maybe it will work fine despite having those two wires disconnected

Edit: With the original power supply, I also remember that the laptop was making a click noise everytime I inserted it, with the new one it doesn't really do that, and there is also an orange light missing but still turns on despite all that, but I may of have notice some minor odd behaviour, will have to test further to confirm though, maybe some expert here can something from that clicky noise, hence the edit
 
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