Hello all:
Does anyone know what are the Apple II+ voltage rails MIN and MAX voltage specs for +12V -12V +5V -5V rails. Also what does one typically see with a few cards in the slots, like two floppy disk controller cards and the other typical cards used, if there is such a thing as the typical expected voltage seen in most Apple II's on the Apple II voltage rails? I have one power supply I tested last night putting out -4.85V and another one puts out -5.35V, on the -5V rail with the same 5 cards plugged into the slots. Seems like a rather large variance on the -5V rail for the same load, as my first impression. Is there a written spec for the limits for these voltages on the Apple II rails in a reference book somewhere? Thanks in advance.
The Apple II Reference Manual on page 92 states nominal voltages per Apple's patent on their original Apple II power supply as follows:
Supply voltages: +5.0, +11.8, -12.0, -5.2
Full load power output: +5v: 2.5 amp, -5V: 250 ma, +12v: 1.5 amp (~ 2.5 amp intermittent**), -12V: 250 ma
These are of course the target/design nominal specs. What I'm looking for are the Min and Max allowed to be in safe operating range on the rails of the Apple II+, in my specific instance, but likely the same safe operating voltages range for all Apple II's. Also if someone has a lot experience with this, voltages on the rails of operating Apple II's, what are the typically voltages measured, most often seen in the real world, and/or what would be the desired rail voltages from real world experience in using Apple II's themselves, or fixing issues with them that are power supply related? I've searched online for the answers to these questions and cannot find it. So, I'm asking all the Apple II gurus here for their real world experience, or if written somewhere ... the Min and Max specs for each voltage rail that one must stay within so as not to potentially damage immediately or long-term, or cause intermittent flakey operation of, any cards plugged into any slot, etc.
I've never had power supply related issues with Apple IIs loaded up with cards.
Back in the 80s I ran a system that looked like this:
Slot 0: 16K RAM card
Slot 1: Parallel printer card
Slot 2: Super Serial Card
Slot 3: 80 Column Card
Slot 4: Disk controller card
Slot 5: Disk controller card
Slot 6: Disk controller card
Slot 7: Clock card
And I ran this 24-7 running a BBS with zero issues.
I don't know what the minimum allowable voltages are but the most important voltage is the +5V one, and it's usualy adjustable with a potentiometer.
I wouldn't worry about it on your machine. Even with 4 mechanical disk drives, the Apple only uses one at a time.
The nominal range for TTL IC's is typically 10 percent of the rated 5VDC, so plus or minus 1/2 volt and the computer should still work.
But going above +5V in general generates more heat to the chip(s) and you can expect a shorter life. In some cases, much shorter.
I like to keep mine within 5 percent of rated voltage but I don't like going more than 0.1 volt above the 5V rail. Others may differ.
Hello Macnoyd,
Thank you. The TTL IC specs is a good guideline to use. And I like your suggestion about keeping the +5V rail even closer to 5V if on the high side. Thanks for pointing that out.
Hello Baldrick,
Sorry, but I disagree and do think power supply voltages on the Apple II rails are very important and one should pay attention to in bringing a 40 year old Apple II+ back to good health. Glad to hear you had absolutely no problems with your Apple II. However, I intend to get mine within +-5% of the nominal voltage design spec voltages listed on page 92 of the Apple II Reference manual, as per Macnoyd's suggestion regarding long-term IC health and system survival, i.e., a high MTBF going forward.
You asked for real world experience...I happen have a lot of real world experience in this area of discussion and I demostrated a near worst case scenario to you with respect to power supply load. As a followup to that description I'll say that I still own the same II+, power supply, cards and drives that ran that BBS, and it does still all work and sees regular use today in my home. Has it been repaired? Sure it has. II+ computers are not very reliable compared to the IIe and IIc. Were the failures power supply related? Unlikely. Most failures I can account for in other ways.
Anyway, you don't have to agree - this is a discussion after all.
And I did say the following:
"I don't know what the minimum allowable voltages are but the most important voltage is the +5V one, and it's usually adjustable with a potentiometer."
The potentiometer is on the power supply PCB, and depending on which company made the power supply it could be in different locations.
WRT Macnoyd's answer, +/- 5% is 4.75V to 5.25V That's a 0.5V range (and quite broad) and anything in between is acceptable.
Put your voltmeter on the power supply terminals with your machine turned on and cards in the slots. Is the 5V line at or around a steady 5 volts? Then it's fine.
Is the 12 volt line at or around a steady 11.8 volts? Then it's fine.
Repeat for the two negative voltages.
What is bad is fluctuating voltages, or voltages with excessive noise or AC on them which would indicate a less than optimal power supply and WILL affect reliability. If that's the case then you should consider a universal power supply upgrade from ReActive Micro.
My rule of thumb has always been ±5% tol. Then again, I also always tended to use regulation with high quality 7805s, 7812s, and whatnot, and a higher voltage/wattage base power source. If I knew that I needed 12V/1A, I used 14.5V/2A and dialed it down with heat dissipation.