Macintosh SE Clock Battery Mod

[quorten]

Recently, I've made a modification to my Macintosh SE to clip out the soldered-on 1/2 AA battery that was near the end of its life and soldered a pin header in its place.  From there, I attached a cable and routed the other end to an easy to reach place in the back right side of the Macintosh SE.  The clock battery is attached via another pin header to the battery holder, and also stored inside a small cardboard box.  Figuring out how to mount the box was a bit of a challenge, but pretty soon I settled on using some tape to secure it to the back of the chassis, and the cables to the external PDS expansion connectors also seem to help hold it in place.

Pretty cool, I made it modular with pin headers so that I can have my choice of what kind of battery to plug in, which is right now a CR2032 battery.  Works like a charm.  No need to go hunting around for a 1/2 AA battery and worrying about the caustic chemicals that might leak out of it when it expires.  I also have enough length to route the cable outside the Macintosh through the security cable connector cutouts if I so wish.

 

[Crutch]

Nice.  I’ve been thinking of doing something similar, currently I use Network Time and PRAM Auto-Restore on my battery-less SE/30 but that doesn’t stop it from starting up in 24-bit mode every time (I think because the 24/32 mode selection happens before PRAM Auto-Restore can run).  I don’t want to install a battery on the motherboard, ever.

I’m guessing that was a 3.6v 1/2A Li battery you replaced with he coin, which is probably 3v.  I’m assuming your SE doesn’t care about the missing 0.6v?

 

[quorten]

Yeah, the original battery was 3.6 V 1/2 AA Li.  The SE works fine with the 3 V coin cell battery.  The clock circuit appears to be fairly robust with low voltages, I believe lower voltages below 2 V cause the clock to start running too slow and down to 1 V the clock doesn't tick at all when the computer is off, but the PRAM can still be preserved at such low voltages.

That being said, time tracking appears to still be pretty accurate at 3 V, one week after the replacement I don't see any signs of the clock running two slow.

 

[beachycove]

Apple's Service Manuals say that if such a battery's voltage falls below 3v, it needs to be replaced. I guess it's possible that this is a precautionary measure.

If you are right that 2v is the real cut-off, then a coin cell on a lead would be a great solution to the battery problem on my SE/30 and Classic II, where the battery is so hard to get at. The leads could be held in a battery holder by means of a dowel, or a piece of crayon, and as you say, the coin could be concealed in a crevice like the security slot. It could also easily be reconnected for use and disconnected during storage. As you say, a battery pack with AAs would also work, rigged with a convenient plug and cycled between different machines if need be. Great solution.

Let us know how you get on, would you?

 

[Compgeke]

I had an SE with a CR2032 mod that worked for over 2 years until I sold it. Still working at the time.

I'll have to see how low a Mac SE will go before losing PRAM\clock settings with a bench PSU. It'll be a lot quicker than waiting for batteries to run down.

 

[quorten]

The Apple Service Manual 3 V threshold is definitely a precautionary measure, the soldered-on VARTA 1/2 AA 3.6 V Li battery I removed from the motherboard must have been the original installed over 30 years ago.  I've had this Macintosh SE for a while, and 10 years ago the clock tended to fall behind by 1 hour after a few weeks.  Then the clock ticked slower and slower until it stopped ticking at all when powered off some time around February earlier this year.  When I measured the in-circuit battery voltage before removal, it was something like 0.56 V.

Not until after I removed the battery did my PRAM settings get reset.  I was amazed the battery would do anything at all at such a low voltage.

So I figure that there is a pretty low operating threshold on the clock circuit, with the main effect on the clock that it will gradually run slower and slower until it stops ticking.  The PRAM has an even lower operating threshold than the clock.

Let us know how you get on, would you?

Sure thing, though for this project as I see things it's pretty much complete as-is.

Another idea to entertain for other compact Macs is that the PDS slot can also be used for routing an external connection for the clock battery.  My expansion card happens not to use all pins on the DE-9 connector, for example.  But, for the time being, I am more than taunted by simply trying to get drivers for the card, Megascreen 3, to work.

 

[Crutch]

Thanks @quorten for inspiring me to do this, I’ve been planning it for maybe a year.  I bought a 1/2” dowel rod and asked the friendly guys at my local Ace Hardware to saw off a 7/8” piece since I don’t have an appropriate saw.  I sanded it down and it’s a good match for a 1/2-AA battery:



So I screwed a tiny #2, 1/4” screw into each end and used them to hold some stripped wires into place, looped around the screws:



It fits nice and snugly into the SE/30 mobo battery cage — and 100% guaranteed never to leak!



I bought a bag of 2-wire connectors, spliced them to my dowel wires on one side, and to the leads on a 2032 coin battery holder I got from Digikey (https://www.digikey.com/product-detail/en/BQ2032-6/BQ2032-6-ND/6200231), then soldered my splices and applied heat shrink.  The connector is to make it easy to change out the battery holder without having to remove the dowel “battery eliminator” from the motherboard (and would be necessary if I wanted to be able to thread the battery line through the security slot):



I then used a Velcro dot to secure the battery holder to a perfect spot on the SE/30 chassis — I did think about threading it thru the security slot but I’m comfortable leaving that coin battery in its protective holder inside the case, plus the SE/30 looks nicer from the outside this way:



And that’s it!  For the first time I have an SE/30 that starts up in 32-bit mode with all the right PRAM settings!  (I’ve been using Network Time and my Asante EN/SE to keep the clock correct, so that was never an issue, but even with the PRAM Auto-Restore cdev running it wouldn’t boot to 32-big mode ... I think because the PRAM restore done by that cdev happens way after the 24/32-bit decision has been locked in.)  Couldn’t be happier!  Thanks again for the inspiration.

 

[LaPorta]

That's quite the feat! I must admit...I am not sure what purpose the dowel serves, however.

 

[Crutch]

It just makes the mod fully reversible, I can pop it out any time and stick a battery in there. 

 

[superjer2000]

@Crutch That is very similar to what I did, except I 3D printed my surrogate battery.  I also used a 1/2 AA battery holder that stays outside of the computer case. 

 

[superjer2000]

@Crutch That is very similar to what I did, except I 3D printed my surrogate battery.  I also used a 1/2 AA battery holder that stays outside of the computer case. 

This is the STL File.

View attachment PRAM Battery.stl

 

[jimjimx]

I think this is too much “hackery” for a $8 battery that lasts 10 years. I always use the correct 1/2 AA battery. There are too many people out there saying they explode, but that doesn’t happen until the battery is completely dead, and the chemistry reverses polarity, creating a “takeoff” reaction.

 

[quorten]

@Crutch Nice!  Glad my post was inspiring.  The surrogate battery is quite a nice way to do battery mods.  (I wish I got the notification earlier... the forum must have been quite busy this time of year.)

Thinking about the possibilities for Macintoshes that were not manufactured with the 1/2 AA battery holder, the ideal modification would probably be to put the 1/2 AA battery holder in place and do the surrogate battery mod if you so wish.  But for me, this was pretty much my first vintage hardware mod that involved soldering.  And, the method of soldering to the old battery leads left over from the clipped-out battery was least invasive.

 

[Crutch]

There are too many people out there saying they explode, but that doesn’t happen until the battery is completely dead, and the chemistry reverses polarity, creating a “takeoff” reaction.

So you’re saying there’s a chance .... 

 

[dcr]

It's also easy to overlook and forget about something that lasts for ten years.

I've had AA and AAA batteries leak in what seemed like under a year, so why take a chance?

And I say that knowing I've probably got batteries leaking in different devices that I've forgotten about.

 

[jimjimx]

So you’re saying there’s a chance .... 

There’s a chance that a alkaline battery will leak. 

 

[jimjimx]

Yeah, the original battery was 3.6 V 1/2 AA Li.  The SE works fine with the 3 V coin cell battery.  The clock circuit appears to be fairly robust with low voltages, I believe lower voltages below 2 V cause the clock to start running too slow and down to 1 V the clock doesn't tick at all when the computer is off, but the PRAM can still be preserved at such low voltages.

That being said, time tracking appears to still be pretty accurate at 3 V, one week after the replacement I don't see any signs of the clock running two slow.

Yeah... NO!

When the battery runs down, the clock won’t slow down.

It won’t have enough voltage to run the oscillator, and the clock will act erratically, or just not work. 

The oscillator can only run at its fixed frequency. 

 

[MacintoshSE1987]

Does anybody know if a Macintosh SE can work without the clock battery?

 

[Phipli]

Does anybody know if a Macintosh SE can work without the clock battery?

Yeah, work fine, just lose a load of settings. Time, mouse speed, desktop pattern, startup disk, volume etc etc.

 

[MacintoshSE1987]

Thanks