Does the LC require a PRAM battery to start?

[ArmorAlley]

I know that the LC475 needs a PRAM battery to start up. Is this also the case for the original LC?

 

[joshc]

No, the oiginal LC will start without one, as does the LC II and LC III/LC III+ and the Performa equivalents of them.

 

[MrFahrenheit]

My experience it requires a PRAM battery to initialize the video.

 

[ArmorAlley]

@joshc & @MrFahrenheit Thanks for your quick replies. I think that you are right about the LC475. The PRAM battery needs to have a sufficient charge for the video output to work but isn't actually necessary to start the machine up.

 

[MrFahrenheit]

@joshc & @MrFahrenheit Thanks for your quick replies. I think that you are right about the LC475. The PRAM battery needs to have a sufficient charge for the video output to work but isn't actually necessary to start the machine up.

There is varying experience on LC models and requiring a PRAM battery.

My own anecdotal evidence is that when there is a red push button reset for the PRAM on the board, it definitely requires a battery (without resorting to trickery of on/off cycles).

I have seen all models of LC-Lc475 with the red button, and I’ve seen LC, LC2 without.

 

[LaPorta]

My LC II will not start correctly without a PRAM battery installed.

 

[joshc]

Interesting. I don't have an LC II anymore to try it out but I am pretty sure the couple I had worked fine without one.

 

[Franklinstein]

Normally no. Rule of thumb is: if it's an '030 or older, or has soft power, it probably doesn't need one. Now this isn't a hard-and-fast rule: there are several machines, notably the 6-slot Mac IIs, that won't even power on without good batteries, but generally the older models don't specifically need a battery to boot. This changed with the '040 and later models with hard power in that they wouldn't boot properly without the battery. The LCs are kind of in an odd bracket in that they can be fussy without a PRAM battery but normally that's because they're not used often enough and/or some capacitors are going bad; normally they don't care that much about the PRAM battery.

Basically the power manager has an internal 8-bit CPU that manages power-on functions and the PRAM battery keeps its parameters loaded and ready to go as soon as it gets main power. If the battery in hard power machines dies or is missing, the CPU loses its data and its operating state so that when power is applied, the power manager's CPU has to boot first before it can perform any useful work. However, by the time it's booted, the power-on initialization window for the Mac has passed, so the machine just sits there; you need to mash reset or do a quick off/on flick of the power button to "jump start" the computer. This procedure cuts the power just long enough to force the other systems in the Mac to go back to their initial power-on state but not long enough to drain the power manager's CPU, so it stays loaded and can properly initialize the system.
Why do soft power machines work without a PRAM battery? Because as soon as they're plugged in, the power manager starts receiving +5v from the power supply, which allows it enough time for it to boot and watch for power-on signals.
Why do weak PRAM batteries cause problems? Because they don't put out enough voltage to maintain the power manager's CPU, so it becomes corrupt and/or crashes. The only cure for that is to hold down the PMU reset button for a while and/or remove the battery and unplug the computer for a bit until the power drains away completely, allowing the power manager's CPU to reset and load with a fresh slate the next time.

 

[MrFahrenheit]

On the LC, my experience has been that if it has a red push button reset it needs a battery if you don’t want to do the fast on/off/on technique.

 

[Verault]

my LC, Lc II, and LC III system (i have 8) all can start fine WITHOUT a pram battery. the psus are problematic on these systems though.

 

[Realitystorm]

I'm putting together a post for my site listing common issues with 1980s and 1990s Macintosh systems. I grouped them in to 4 main categories: will not start, starts but has a blank screen, starts and displays an error code, starts and displays a blinking question mark.

For the first category, won't start, I'm trying to create a list of systems that will not start without a PRAM battery. I've found two KB articles so far: Color Classic and LC/Performa 5xx systems (KB12241), and the Macintosh II, IIx, and IIfx (KB2188). For the first article, I'm not sure if the CC etc. needs the PRAM battery to boot, or you can also just reset the PRAM to boot. My CC is currently in pieces and I can't remember if it needed a working battery to start or not. What other systems need a PRAM battery to start? (I'm aware of the jumpstarting tricks, I mean without doing those)

For the second category, blank screen, I found a singled KB article listing: Quadra 605, Performa 475, Performa 476, LC 475, Centris 660AV, Quadra 660AV, Power Macintosh 6100, and the Performa 61XX (KB20328). Are there any others?

 

[naruse]

Interesting -- Does anyone know if by using a CR32 battery instead of the AA battery, will this be enough to boot the LC475?; or are these logic boards required to just use AA batteries

 

[Arbee]

If the voltage is high enough it'll work. I don't know what the valid range is for the 68HC05 off the top of my head, but I'd think 3 to 3.5 would probably cover it.

 

[chiptripper]

I use 3.6v rechargeable CR2032 batteries with a SiliconInsider adapter, works great.

 

[volvo242gt]

3 volts is enough. The old Varta CR14250 PRAM batteries are only 3 volts. Machines with them usually are fine.

So, a meowTOAST or Siliconinsider adapter with a CR2032 should suffice.