Supplying adequate power

Hardware questions and modifications

Supplying adequate power

Postby Cooljerk » Thu Nov 05, 2020 4:08 pm

I'm looking to expand my PCjr and I have some questions about power supplies. I know the stock PSU is supposed to be inadequate compared to the XT PSU and thus it's sort of not recommended to pull through much power through the sidecar slot. But I've also read that just a few sidecards should be fine.

I'm not looking to daisy chain a bunch of sidecars, all I want to attach to my PCjr is jr-ide with a compact flash kit installed. I actually have an additional power supply sidecar if more power is needed, but I'm already not a big fan of the large pcjr power brick, and am looking to avoid having two of them if possible.

So that brings me to the pico psu. I saw a youtube series where someone repaired a pcjr and he tried both a pico psu and a full internal psu replacement, and both options seemed fine. I'm not so interested in the full internal psu replacement, because I also want to keep my PCjr running as cool as possible, so I'm more focused on the pico psu.

Everything seems fine except that the project page for the pcjr atx power supply adapter specifically addresses pico psu as I'm describing:

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

Q: With this I can power all my side cars without a power side car right?

A: I am strongly recommending against that. The PCjr system board wasn't design to handle high power delivery through the expansion connector. I don't know what the consequences of doing so would be.


I am no electrical engineer, I much prefer to defer to experts when it comes to matters like these. How warranted is this warning? Would a jr-ide be too much drain for a single pico psu like this? Should I be extra cautious and just use the power supply sidecar as well?
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Re: Supplying adequate power

Postby Trixter » Thu Nov 05, 2020 6:31 pm

I'm powering a jrIDE and a parallel-port sidecar with just the stock power supply, so you should be fine.

If you want to load up a PCjr with sidecars, the recommendation from IBM is that every 4th sidecar should be a power sidecar.
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Re: Supplying adequate power

Postby Cooljerk » Fri Nov 06, 2020 11:30 pm

Much appreciate the peace of mind!

Along the same lines, would you happen to know if a gotek replacement drive would consume more or less power than the normal floppy? I would guess less, right? No motor to drive?
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Re: Supplying adequate power

Postby Trixter » Sat Nov 07, 2020 9:25 am

Definitely less :-)
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Re: Supplying adequate power

Postby FortMax » Sat Nov 07, 2020 11:14 am

Way less. No spindle motor, no stepper motor, and I'd be surprised if a flash drive needed more power 2 drive heads.
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