I looked at the output for the power supply and it said, +12V -12V and +5V
but i know the apple II requires a -5V
my question is,
are both the 12V and 5V needed to power up my apple?
what does the 12V do and what does the 5V do for the computer?
Also, is there a way to make this work, or should i return the power supply ?
The Buggie power supplies used older IBM ATX power supplies which had a -5v rail. Modern power supplies do not contain the -5v rail so you would need to get the littlepower adapter from ultimateapple2.com:
https://ultimateapple2.com/catalogzenQI/index.php?main_page=product_info&cPath=1_6&products_id=8
And/or, build your own. The schematic to build your own can be found at this website:
http://www.harrowalsh.de/Elektronik/APPLEBOX/powersupply_upgrading.htm
I had a discussion with two experts on the subject and I will post the relevant information here but be aware that they do not agree:
Me:
It seems that my new power supply is missing the -5v rail. Wikipedia says, "Pin 20 (formerly −5 V, white wire) is absent in current power supplies; it was optional in ATX and ATX12V ver. 1.2, and deleted as of ver. 1.3.".
Do you have any suggestions on how to deal with this problem?
Expert #1:
Noted that your power supply lacks the -5V line. All standard Apple II power supplies have all four voltages: +5v +12v -12v -5v . All the power supplies I have sold, have the four required voltages.
The two minus lines, -5v and -12v, have low amperage outputs. They are there as a safety feature; to provide independent measures of the voltages against which the positive line outputs can be compared. In my opinion, the power supplies that lack the -5v line lose the chance to shut down the power supply in the event that the +5v line goes wild, straying outside its acceptable limits. This is a compromise with safety...
...Hooking one up in the absence of the -5v line is too risky. Best to search for a different power supply that has all four of the voltages, including the -5v line.
Expert #2:
Hello,
that statement is only partially true... in fact in old Apple II´s (those with the onboard 4116 RAM chips and with the language card)... those RAM chips require -5V power otherwise they won´t work correctly due to the missing powerline... but they only require a very small amount of power so the use won´t exceed the 0.4 Amp limit that I've explained.... later Apple II models without 4116 RAM chips (like later Apple IIe´s and Apple II GS ) don´t need the -5 Volt.
The +5 Volt from the PC power suplies have internal control to the +5 Volt so there is only the bridge required from the sencecontrol...
Me:
Any electrical device has a MTBF (Mean time before failure) and sooner or later any power supply will reach it, no matter what. Also, any component within an electronic device has it's own MTBF. This MTBF is determined by the manufacturer. The time length may be bloated but you can be sure that things will break either at the MTBF or earlier.
The other reason why I wish to do it this way is convenience. Most power supplies you can get nowadays have no -5v rail. The only place to get a new power supply with a -5v rail is ebay. The existence of the littlepower adapter is proof enough to me that it is a viable product.
Expert #1:
...So, the - 5 volts line is for the RAMS??????? I still don't understand why the +5volt line would not be enough... MTBF: Even if a switching power supply failed, it would be unlikely to do damage. The many protection circuits will shut it down, turning it off, if the output voltage strayed beyond its limits.
Hello,
The +5V is needed for all the 74LS chips and the CPU.
The 4116 RAM chips need the +12V and -5V respectively on pin 8 and 1 (+5V is also required on pin 9).
And finally, the -12V is needed on the Apple II MM5740 keyboard encoder on pin 18 and on pin 27 of the AY-5-3600 keyboard encoder in a II+.
So basically, all the voltages are required to operate a standard (non modded) Apple II or II+.
+12V is also use by the Disk II.
And all these voltages are available on the peripheral slots. So some extension cards may also use them.
Hello pc154864,
instead of moaning around, it would be usefull if you finally start to make more specific questions !
unless you don´t specify your questions better - there are different answers correct !
At Apple II, Apple II+ and Apple II europlus -5 Volt is mandatory and computer won´t startup without it !
At Apple //e -5 Volt might be left away unless one of the interfacecards demands such voltage....
so as explained above answer from expert #2 is correct for Apple II, II+ and II europlus
as also explained from amauget !
the mess is that your questions allways lack of precise specs which computer you are working at...
just as mentioned about missing information: there are thousands of different power supplies !!!
Which one are you talking about ?????
just for information if you are using supply for Apple II+ or //e see pinouts of RAM chips below :
and as visible in pinouts above +12 Volt is also requested for RAM !
But besides +12 Volt is also requested for the Diskette interface for the Apple II Diskdrive !
i hope you first think about your questions in future a little bit better and make more complete
informations about the target of your questions availiable... we just are not able to just guess around
in Nirvana without vital informations...
How about starting first with reading a book as mentioned in earlier postings ???
Maybe it´s a good idea to start with this book that explains the basics of the Apple II series:
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/Jim%20Sather%20-%20Understanding%20the%20Apple%20II.pdf
speedyG
I'm lovin' that diagram, speedyG! I don't recall having seen that information presented anywhere as clearly as that.