DC Power Brick for PCjr

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DC Power Brick for PCjr

Post by psergiu »


Has anyone attempted to replace the 18V AC power brick for a PCjr with a DC power supply (repurposed laptop charger) ? The rectifier bridge should not care if the incoming power is 0Hz

Thanks !
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Re: DC Power Brick for PCjr

Post by chuckphd53 »

I agree it should work, using pins 1 and 3 in either order, if the Current rating is ok give it a try..
May want to try in on the bench with the power supply not plugged in first.
I dont think you will get the -12v as it needs to be plugged in if memory serves me,
but you can measure the 5V to see.

Look for anything getting warm :)

be great to hear your results..

“I never commit to memory anything that can easily be looked up in a book.” (AE)
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Re: DC Power Brick for PCjr

Post by VicViper »

The DC adapter will almost certainly NOT work.

The linear PSU in the PCjr requires AC in order for it to create the +12v +5v and -12v the system requires.

I have replaced the PCU in my PCjr with an ATX adapter designed by AkBKukU (See link) and a PicoATX power supply with a 3D printed bracket in the back that holds the new power jack for the 12v DC power supply. I used a 120 W PicoATX power supply and a 100 W 12 volt power adapter. Both are being de-rated quite a bit as the PCjr even with a Racore 2nd disk drive and side car being powered off it with an adapter I made doesn't draw anywhere near that.

https://akbkuku.com/store/p/1/IBM-PCjr- ... y-Adapter/

The PicoATX and 12Volt adapter I used are from www.mini-box.com
100w (12v/8.33A) AC-DC Power Adapter with Power Cord

picoPSU-120, 120w output, 12v input DC-DC Power Supply

I also did power usage measurements both before and after the upgrade. The power usage went down so much that I could just remove the fan entirely as the only major source of heat in the machine is the linear power supply. The wattage use is cut almost in half and after hours of use, the machine is only a little bit warm. But the new PSU adapter board has a fan connector so you can keep it if you like.

I would also recommend an upgrade to the modern Static version of the NEC V20 CPU as it is also way more power efficient. I measured the power usage of the Intel 8088 from the PCjr and the NEC V20 using a small 8088 dev board. After subtracting the power using of the dev board without the CPU the Intel 8088 from the PCjr uses 0.56 Watts, the Static version of the NEC V20 uses 0.06 Watts. Almost nothing.

The part number for the most efficient version of the V20 is D70108HCZ-16. It can go to 16 MHz, but will happily run at 4.7MHz of your PCjr Motherboard.

I also have 3 original PCjr 16V AC adapters I don't need anymore as well as an internal IBM OEM PCjr PSU. PM me if you want them. I only ask shipping costs. They were working perfectly when I pulled them out.
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