Developing a replacement power supply

[jmetal88]

I mentioned in another thread that I might be interested in developing a replacement power supply board for the PCjr, but I'm coming up with some conflicting information.

My tech ref lists the pinout of the power board as +12V, GND, +5V, GND, +12V. This is obviously incorrect. According to the text description in the same book, the pinout should have been listed as -6V, GND, +5V, GND, +12V.

Now, I've read in other forum posts online that the -6V, GND, +5V, GND, +12V listing should be correct, although one post says the negative output is -12V nominally, and it drops to -6V under load. Thing is, I've checked my power supply both by itself and while it's powering the PCjr and it puts out -12V on that pin all the time, even under load.

So, I guess I should ask, if I design a new power supply board, should I be putting -6V or -12V on that pin? Is the tech ref incorrect on that number, or is there just a wide tolerance on that voltage?

[jltursan]

IMHO the correct value is -12V; maybe checking the PSU circuitry that leads to this pin an expert can confirm this...

[Eric]

I'm not sure if it's funny or just a headache that the information in the technical reference manual has this wrong.

[Brutman]

I should have posted this sooner; your post reminded me.

Do not believe everything that you read - the technical reference manual in particular had some errata that were fixed with an update packet. It is very hard to tell if you have the correct version; the update packet usually just replaced the old pages and did not make a note that you were now looking at the newer pages.


Mike